<p>Frontal (<b>A´, B´</b> and <b>C´</b>) and horizontal (all other)... more <p>Frontal (<b>A´, B´</b> and <b>C´</b>) and horizontal (all other) views of Flybow clones (semischematic drawings in <b>A´´, B´´, C´´</b> and <b>D,</b> and composite confocal images in all other) resembling NB7-2 lineage. Fibre projections show very little modulation across the segments: an ipsilateral descending interneuronal fascicle in a dorsal position within the connective and a contralateral bundle through the posterior commissure. Cell numbers are significantly reduced in MN (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0191453#pone.0191453.s003" target="_blank">S1 Table</a>).</p
<p>Frontal (<b>A´, B´, A´* and B´*</b>) and horizontal (all other) views of Fly... more <p>Frontal (<b>A´, B´, A´* and B´*</b>) and horizontal (all other) views of Flybow clones (semischematic drawings in <b>A´´, B´´ and C</b> and composite confocal stacks in all other images) resembling NB5-6 lineage. In thoracic segments (<b>C</b>) NB5-6 is a neuroglioblast that gives rise to about 5 glial cells and several interneurons that project through both commissures and form short axons along the ipsilateral connective in both directions [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0191453#pone.0191453.ref014" target="_blank">14</a>]. Although Flybow clones generated with an Elav driver are expected to show only low hue-expression in glial cells, the clones reveal a couple of cells at the cortex margin with glial-like shape (green arrowheads in the confocal images and green cells in <b>A´´ and B´´</b>); <b>A* to B´*</b> zoom into single layers of the image stacks in <b>A</b> and <b>B</b> to show the typical morphology of subperineural glial cells: in a location directly at the margin of the nerve chord with long and thin protrusions that cover the cortex. The projection pattern of the LB lineage largely resembles the thoracic one, but shows an additional long ipsilateral projection in anterior direction (red arrowhead in <b>B</b> and <b>B´´)</b>. In MX the lineage shows reduced projections.</p
the gap between postembryonic cell lineages and identified embryonic neuroblasts in the ventral n... more the gap between postembryonic cell lineages and identified embryonic neuroblasts in the ventral nerve cord of
One of the initial steps of neurogenesis in the Drosophila embryo is the delamination of a stereo... more One of the initial steps of neurogenesis in the Drosophila embryo is the delamination of a stereotype set of neural progenitor cells (neuroblasts) from the neuroectoderm. The time window of neuroblast segregation has been divided into five successive waves (S1-S5) in which subsets of neuroblasts with specific identities are formed. To test when identity specification of the various neuroblasts takes place and whether extrinsic signals are involved, we have performed heterochronic transplantation experiments. Single neuroectodermal cells from stage 10 donor embryos (after S2) were transplanted into the neuroectoderm of host embryos at stage 7 (before S1) and vice versa. The fate of these cells was uncovered by their lineages at stage 16/17. Transplanted cells adjusted their fate to the new temporal situation. Late neuroectodermal cells were able to take over the fate of early (S1/S2) neuroblasts. The early neuroectodermal cells preferentially generated late (S4/S5) neuroblasts, despi...
Cells located at the midline of the developing central nervous system perform a number of conserv... more Cells located at the midline of the developing central nervous system perform a number of conserved functions during the establishment of the lateral CNS. The midline cells of the Drosophila CNS were previously shown to be required for correct pattern formation in the ventral ectoderm and for the induction of specific mesodermal cells. Here we investigated whether the midline cells are required for the correct development of lateral CNS cells as well. Embryos that lack midline cells through genetic ablation show a 15% reduction in the number of cortical CNS cells. A similar thinning of the ventral nerve cord can be observed following mechanical ablation of the midline cells. We have identified a number of specific neuronal and glial cell markers that are reduced in CNS midline-less embryos (in single-minded embryos, in early heat-shocked Notch(ts1) embryos or in embryos where we mechanically ablated the midline cells). Genetic data suggest that both neuronal and glial midline cell l...
The Drosophila ventral nerve cord (vNC) derives from a stereotyped population of neural stem cell... more The Drosophila ventral nerve cord (vNC) derives from a stereotyped population of neural stem cells, neuroblasts (NBs), each of which gives rise to a characteristic cell lineage. The mechanisms leading to the specification and differentiation of these lineages are largely unknown. Here we analyse mechanisms leading to cell differentiation within the NB 7–3 lineage. Analogous to the grasshopper, NB 7–3 is the progenitor of the Drosophila vNC serotonergic neurons. The zinc finger protein Eagle (Eg) is expressed in NB 7–3 just after delamination and is present in all NB 7–3 progeny until late stage 17. DiI cell lineage tracing and immunocytochemistry reveal that eg is required for normal pathfinding of interneuronal projections and for restricting the cell number in the thoracic NB 7–3 lineage. Moreover, eg is required for serotonin expression. Ectopic expression of Eg protein forces specific additional CNS cells to enter the serotonergic differentiation pathway. Like NB 7–3, the progen...
The Drosophila central nervous system derives from neural precursor cells, the neuroblasts (NBs),... more The Drosophila central nervous system derives from neural precursor cells, the neuroblasts (NBs), which are born from the neuroectoderm by the process of delamination. Each NB has a unique identity, which is revealed by the production of a characteristic cell lineage and a specific set of molecular markers it expresses. These NBs delaminate at different but reproducible time points during neurogenesis (S1-S5) and it has been shown for early delaminating NBs (S1/S2) that their identities depend on positional information conferred by segment polarity genes and dorsoventral patterning genes. We have studied mechanisms leading to the fate specification of a set of late delaminating neuroblasts, NB 6-4 and NB 7-3, both of which arise from the engrailed (en) expression domain, with NB 6-4 delaminating first. In contrast to former reports, we did not find any evidence for a direct role of hedgehog in the process of NB 7-3 specification. Instead, we present evidence to show that the interpl...
The Drosophila ventral nerve cord derives from a stereotype population of about 30 neural stem ce... more The Drosophila ventral nerve cord derives from a stereotype population of about 30 neural stem cells, the neuroblasts, per hemineuromere. Previous experiments provided indications for inductive signals at ventral sites of the neuroectoderm that confer neuroblast identities. Using cell lineage analysis, molecular markers and cell transplantation, we show here that EGF receptor signalling plays an instructive role in CNS patterning and exerts differential effects on dorsoventral subpopulations of neuroblasts. The Drosophila EGF receptor (DER) is capable of cell autonomously specifiying medial and intermediate neuroblast cell fates. DER signalling appears to be most critical for proper development of intermediate neuroblasts and less important for medial neuroblasts. It is not required for lateral neuroblast lineages or for cells to adopt CNS midline cell fate. Thus, dorsoventral patterning of the CNS involves both DER-dependent and -independent regulatory pathways. Furthermore, we dis...
The numbers and types of progeny cells generated by neural stem cells in the developing CNS are a... more The numbers and types of progeny cells generated by neural stem cells in the developing CNS are adapted to its region-specific functional requirements. In Drosophila, segmental units of the CNS develop from well-defined patterns of neuroblasts. Here we constructed comprehensive neuroblast maps for the three gnathal head segments. Based on the spatiotemporal pattern of neuroblast formation and the expression profiles of 46 marker genes (41 transcription factors), each neuroblast can be uniquely identified. Compared with the thoracic ground state, neuroblast numbers are progressively reduced in labial, maxillary and mandibular segments due to smaller sizes of neuroectodermal anlagen and, partially, to suppression of neuroblast formation and induction of programmed cell death by the Hox gene Deformed. Neuroblast patterns are further influenced by segmental modifications in dorsoventral and proneural gene expression. With the previously published neuroblast maps and those presented here...
The clarification of complete cell lineages, which are produced by specific stem cells, is fundam... more The clarification of complete cell lineages, which are produced by specific stem cells, is fundamental for understanding mechanisms, controlling the generation of cell diversity and patterning in an emerging tissue. In the developing Central Nervous System (CNS) of Drosophila, neural stem cells (neuroblasts) exhibit two periods of proliferation: During embryogenesis they produce primary lineages, which form the larval CNS. After a phase of mitotic quiescence, a subpopulation of them resumes proliferation in the larva to give rise to secondary lineages that build up the CNS of the adult fly. Within the ventral nerve cord (VNC) detailed descriptions exist for both primary and secondary lineages. However, while primary lineages have been linked to identified neuroblasts, the assignment of secondary lineages has so far been hampered by technical limitations. Therefore, primary and secondary neural lineages co-existed as isolated model systems. Here we provide the missing link between th...
Advances in Experimental Medicine and Biology, 2008
ABSTRACT The central nervous system (CNS) represents the organ with the highest structural and fu... more ABSTRACT The central nervous system (CNS) represents the organ with the highest structural and functional complexity. Accordingly, uncovering the mechanisms leading to cell diversity, patterning and connectivity in the CNS is one of the major challenges in developmental biology. The developing CNS of the fruitfly Drosophila melanogaster is an ideal model system to study these processes. Several principle questions regarding neurogenesis (like stem cell formation, cell fate specification, axonal pathfinding) have been addressed in Drosophila by focusing on the relatively simply structured truncal parts of the nervous system. However, information processing (e.g. vision, olfaction), behavior, learning and memory require highly specialized structures, which are located in the brain. Owing to much higher complexity and hidden segmental organisation our understanding of brain development is still quite rudimentary. Considerable advances have been made recently in bringing the resolution of brain structures to the level of individual cells and their lineages, which significantly facilitates investigations into the mechanisms controlling brain development. This book provides an overview of some major facets of recent research on Drosophila brain development. The individual chapters were written by experts in each field. V. Hartenstein et al. survey the generic cell types that make up the developing brain and describe the morphogenesis of neural lineages and their relationship to neuropile compartments in the larval brain. Recent findings on anterioposterior regionalization and on dorsoventral patterning in the embryonic brain are reviewed in the chapters by R. Lichtneckert and H. Reichert and by R. Urbach and G. Technau, respectively. Both processes show striking parallels between Drosophila and mouse. Photoactivated gene expression as a means for tracing cell fate through embryonic brain development is demonstrated in J. Minden´s chapter. At present, the best characterized neural network on the developmental, structural, and functional level is the chemosensory system, to which three chapters are devoted: R. Stocker´s chapter covers the design of the larval chemosensory system and shows that it prefigures the adult system. V. Rodrigues and T. Hummel summarize recent findings on the specification and connectivity development of the adult olfactory receptor neurons. P. Laissue and B. Vosshall review the molecular biology, neuroanatomy and function of the adult olfactory system. A further focus of research is the visual system, with the optic lobes comprising about half of the adult fly brain. The genetic and cellular principles which direct the assembly of the optic lobes are highlighted in the chapter by K. Fischbach and P. Hiesinger. The central brain harbors distinct neuropils like the central complex and the mushroom bodies, as well as “diffused neuropiles” which lack clearly demarcated structures. K. Ito and T. Awasaki review the organization of the adult central brain and show how its complex architecture evolves from clonally related neural circuits. This book will be helpful to those who want to study brain development in the fly. As knowledge extracted from the Drosophila model has often proven to be of more general relevance, comparative aspects are included in most chapters. Therefore, this book should also be useful for researchers working on brain development in other organisms and on brain evolution, as well as for instructors and advanced students in the field of developmental neurobiology.
Development of the nervous system and establishment of complex neuronal networks require the conc... more Development of the nervous system and establishment of complex neuronal networks require the concerted activity of different signalling events and guidance cues, which include Netrins and their receptors. In Drosophila, two Netrins are expressed during embryogenesis by cells of the ventral midline and serve as attractant or repellent cues for navigating axons. We asked whether glial cells, which are also motile, are guided by similar cues to axons, and analysed the influence of Netrins and their receptors on glial cell migration during embryonic development. We show that in Netrin mutants, two distinct populations of glial cells are affected: longitudinal glia (LG) fail to migrate medially in the early stages of neurogenesis, whereas distinct embryonic peripheral glia (ePG) do not properly migrate laterally into the periphery. We further show that early Netrin-dependent guidance of LG requires expression of the receptor Frazzled (Fra) already in the precursor cell. At these early st...
The central nervous system is composed of segmental units (neuromeres), the size and complexity o... more The central nervous system is composed of segmental units (neuromeres), the size and complexity of which evolved in correspondence to their functional requirements. In Drosophila, neuromeres develop from populations of neural stem cells (neuroblasts) that delaminate from the early embryonic neuroectoderm in a stereotyped spatial and temporal pattern. Pattern units closely resemble the ground state and are rather invariant in thoracic (T1-T3) and anterior abdominal (A1-A7) segments of the embryonic ventral nerve cord. Here, we provide a comprehensive neuroblast map of the terminal abdominal neuromeres A8-A10, which exhibit a progressively derived character. Compared with thoracic and anterior abdominal segments, neuroblast numbers are reduced by 28% in A9 and 66% in A10 and are almost entirely absent in the posterior compartments of these segments. However, all neuroblasts formed exhibit serial homology to their counterparts in more anterior segments and are individually identifiable...
Locomotion relies on stable attachment of muscle fibres to their target sites, a process that all... more Locomotion relies on stable attachment of muscle fibres to their target sites, a process that allows for muscle contraction to generate movement. Here, we show that glide/gcm and glide2/gcm2, the fly glial cell determinants, are expressed in a subpopulation of embryonic tendon cells and required for their terminal differentiation. By using loss-of-function approaches, we show that in the absence of both genes, muscle attachment to tendon cells is altered, even though the molecular cascade induced by stripe, the tendon cell determinant, is normal. Moreover, we show that glide/gcm activates a new tendon cell gene independently of stripe. Finally, we show that segment polarity genes control the epidermal expression of glide/gcm and determine, within the segment,whether it induces glial or tendon cell-specific markers. Thus, under the control of positional cues, glide/gcm triggers a new molecular pathway involved in terminal tendon cell differentiation, which allows the establishment of...
<p>Frontal (<b>A´, B´</b> and <b>C´</b>) and horizontal (all other)... more <p>Frontal (<b>A´, B´</b> and <b>C´</b>) and horizontal (all other) views of Flybow clones (semischematic drawings in <b>A´´, B´´, C´´</b> and <b>D,</b> and composite confocal images in all other) resembling NB7-2 lineage. Fibre projections show very little modulation across the segments: an ipsilateral descending interneuronal fascicle in a dorsal position within the connective and a contralateral bundle through the posterior commissure. Cell numbers are significantly reduced in MN (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0191453#pone.0191453.s003" target="_blank">S1 Table</a>).</p
<p>Frontal (<b>A´, B´, A´* and B´*</b>) and horizontal (all other) views of Fly... more <p>Frontal (<b>A´, B´, A´* and B´*</b>) and horizontal (all other) views of Flybow clones (semischematic drawings in <b>A´´, B´´ and C</b> and composite confocal stacks in all other images) resembling NB5-6 lineage. In thoracic segments (<b>C</b>) NB5-6 is a neuroglioblast that gives rise to about 5 glial cells and several interneurons that project through both commissures and form short axons along the ipsilateral connective in both directions [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0191453#pone.0191453.ref014" target="_blank">14</a>]. Although Flybow clones generated with an Elav driver are expected to show only low hue-expression in glial cells, the clones reveal a couple of cells at the cortex margin with glial-like shape (green arrowheads in the confocal images and green cells in <b>A´´ and B´´</b>); <b>A* to B´*</b> zoom into single layers of the image stacks in <b>A</b> and <b>B</b> to show the typical morphology of subperineural glial cells: in a location directly at the margin of the nerve chord with long and thin protrusions that cover the cortex. The projection pattern of the LB lineage largely resembles the thoracic one, but shows an additional long ipsilateral projection in anterior direction (red arrowhead in <b>B</b> and <b>B´´)</b>. In MX the lineage shows reduced projections.</p
the gap between postembryonic cell lineages and identified embryonic neuroblasts in the ventral n... more the gap between postembryonic cell lineages and identified embryonic neuroblasts in the ventral nerve cord of
One of the initial steps of neurogenesis in the Drosophila embryo is the delamination of a stereo... more One of the initial steps of neurogenesis in the Drosophila embryo is the delamination of a stereotype set of neural progenitor cells (neuroblasts) from the neuroectoderm. The time window of neuroblast segregation has been divided into five successive waves (S1-S5) in which subsets of neuroblasts with specific identities are formed. To test when identity specification of the various neuroblasts takes place and whether extrinsic signals are involved, we have performed heterochronic transplantation experiments. Single neuroectodermal cells from stage 10 donor embryos (after S2) were transplanted into the neuroectoderm of host embryos at stage 7 (before S1) and vice versa. The fate of these cells was uncovered by their lineages at stage 16/17. Transplanted cells adjusted their fate to the new temporal situation. Late neuroectodermal cells were able to take over the fate of early (S1/S2) neuroblasts. The early neuroectodermal cells preferentially generated late (S4/S5) neuroblasts, despi...
Cells located at the midline of the developing central nervous system perform a number of conserv... more Cells located at the midline of the developing central nervous system perform a number of conserved functions during the establishment of the lateral CNS. The midline cells of the Drosophila CNS were previously shown to be required for correct pattern formation in the ventral ectoderm and for the induction of specific mesodermal cells. Here we investigated whether the midline cells are required for the correct development of lateral CNS cells as well. Embryos that lack midline cells through genetic ablation show a 15% reduction in the number of cortical CNS cells. A similar thinning of the ventral nerve cord can be observed following mechanical ablation of the midline cells. We have identified a number of specific neuronal and glial cell markers that are reduced in CNS midline-less embryos (in single-minded embryos, in early heat-shocked Notch(ts1) embryos or in embryos where we mechanically ablated the midline cells). Genetic data suggest that both neuronal and glial midline cell l...
The Drosophila ventral nerve cord (vNC) derives from a stereotyped population of neural stem cell... more The Drosophila ventral nerve cord (vNC) derives from a stereotyped population of neural stem cells, neuroblasts (NBs), each of which gives rise to a characteristic cell lineage. The mechanisms leading to the specification and differentiation of these lineages are largely unknown. Here we analyse mechanisms leading to cell differentiation within the NB 7–3 lineage. Analogous to the grasshopper, NB 7–3 is the progenitor of the Drosophila vNC serotonergic neurons. The zinc finger protein Eagle (Eg) is expressed in NB 7–3 just after delamination and is present in all NB 7–3 progeny until late stage 17. DiI cell lineage tracing and immunocytochemistry reveal that eg is required for normal pathfinding of interneuronal projections and for restricting the cell number in the thoracic NB 7–3 lineage. Moreover, eg is required for serotonin expression. Ectopic expression of Eg protein forces specific additional CNS cells to enter the serotonergic differentiation pathway. Like NB 7–3, the progen...
The Drosophila central nervous system derives from neural precursor cells, the neuroblasts (NBs),... more The Drosophila central nervous system derives from neural precursor cells, the neuroblasts (NBs), which are born from the neuroectoderm by the process of delamination. Each NB has a unique identity, which is revealed by the production of a characteristic cell lineage and a specific set of molecular markers it expresses. These NBs delaminate at different but reproducible time points during neurogenesis (S1-S5) and it has been shown for early delaminating NBs (S1/S2) that their identities depend on positional information conferred by segment polarity genes and dorsoventral patterning genes. We have studied mechanisms leading to the fate specification of a set of late delaminating neuroblasts, NB 6-4 and NB 7-3, both of which arise from the engrailed (en) expression domain, with NB 6-4 delaminating first. In contrast to former reports, we did not find any evidence for a direct role of hedgehog in the process of NB 7-3 specification. Instead, we present evidence to show that the interpl...
The Drosophila ventral nerve cord derives from a stereotype population of about 30 neural stem ce... more The Drosophila ventral nerve cord derives from a stereotype population of about 30 neural stem cells, the neuroblasts, per hemineuromere. Previous experiments provided indications for inductive signals at ventral sites of the neuroectoderm that confer neuroblast identities. Using cell lineage analysis, molecular markers and cell transplantation, we show here that EGF receptor signalling plays an instructive role in CNS patterning and exerts differential effects on dorsoventral subpopulations of neuroblasts. The Drosophila EGF receptor (DER) is capable of cell autonomously specifiying medial and intermediate neuroblast cell fates. DER signalling appears to be most critical for proper development of intermediate neuroblasts and less important for medial neuroblasts. It is not required for lateral neuroblast lineages or for cells to adopt CNS midline cell fate. Thus, dorsoventral patterning of the CNS involves both DER-dependent and -independent regulatory pathways. Furthermore, we dis...
The numbers and types of progeny cells generated by neural stem cells in the developing CNS are a... more The numbers and types of progeny cells generated by neural stem cells in the developing CNS are adapted to its region-specific functional requirements. In Drosophila, segmental units of the CNS develop from well-defined patterns of neuroblasts. Here we constructed comprehensive neuroblast maps for the three gnathal head segments. Based on the spatiotemporal pattern of neuroblast formation and the expression profiles of 46 marker genes (41 transcription factors), each neuroblast can be uniquely identified. Compared with the thoracic ground state, neuroblast numbers are progressively reduced in labial, maxillary and mandibular segments due to smaller sizes of neuroectodermal anlagen and, partially, to suppression of neuroblast formation and induction of programmed cell death by the Hox gene Deformed. Neuroblast patterns are further influenced by segmental modifications in dorsoventral and proneural gene expression. With the previously published neuroblast maps and those presented here...
The clarification of complete cell lineages, which are produced by specific stem cells, is fundam... more The clarification of complete cell lineages, which are produced by specific stem cells, is fundamental for understanding mechanisms, controlling the generation of cell diversity and patterning in an emerging tissue. In the developing Central Nervous System (CNS) of Drosophila, neural stem cells (neuroblasts) exhibit two periods of proliferation: During embryogenesis they produce primary lineages, which form the larval CNS. After a phase of mitotic quiescence, a subpopulation of them resumes proliferation in the larva to give rise to secondary lineages that build up the CNS of the adult fly. Within the ventral nerve cord (VNC) detailed descriptions exist for both primary and secondary lineages. However, while primary lineages have been linked to identified neuroblasts, the assignment of secondary lineages has so far been hampered by technical limitations. Therefore, primary and secondary neural lineages co-existed as isolated model systems. Here we provide the missing link between th...
Advances in Experimental Medicine and Biology, 2008
ABSTRACT The central nervous system (CNS) represents the organ with the highest structural and fu... more ABSTRACT The central nervous system (CNS) represents the organ with the highest structural and functional complexity. Accordingly, uncovering the mechanisms leading to cell diversity, patterning and connectivity in the CNS is one of the major challenges in developmental biology. The developing CNS of the fruitfly Drosophila melanogaster is an ideal model system to study these processes. Several principle questions regarding neurogenesis (like stem cell formation, cell fate specification, axonal pathfinding) have been addressed in Drosophila by focusing on the relatively simply structured truncal parts of the nervous system. However, information processing (e.g. vision, olfaction), behavior, learning and memory require highly specialized structures, which are located in the brain. Owing to much higher complexity and hidden segmental organisation our understanding of brain development is still quite rudimentary. Considerable advances have been made recently in bringing the resolution of brain structures to the level of individual cells and their lineages, which significantly facilitates investigations into the mechanisms controlling brain development. This book provides an overview of some major facets of recent research on Drosophila brain development. The individual chapters were written by experts in each field. V. Hartenstein et al. survey the generic cell types that make up the developing brain and describe the morphogenesis of neural lineages and their relationship to neuropile compartments in the larval brain. Recent findings on anterioposterior regionalization and on dorsoventral patterning in the embryonic brain are reviewed in the chapters by R. Lichtneckert and H. Reichert and by R. Urbach and G. Technau, respectively. Both processes show striking parallels between Drosophila and mouse. Photoactivated gene expression as a means for tracing cell fate through embryonic brain development is demonstrated in J. Minden´s chapter. At present, the best characterized neural network on the developmental, structural, and functional level is the chemosensory system, to which three chapters are devoted: R. Stocker´s chapter covers the design of the larval chemosensory system and shows that it prefigures the adult system. V. Rodrigues and T. Hummel summarize recent findings on the specification and connectivity development of the adult olfactory receptor neurons. P. Laissue and B. Vosshall review the molecular biology, neuroanatomy and function of the adult olfactory system. A further focus of research is the visual system, with the optic lobes comprising about half of the adult fly brain. The genetic and cellular principles which direct the assembly of the optic lobes are highlighted in the chapter by K. Fischbach and P. Hiesinger. The central brain harbors distinct neuropils like the central complex and the mushroom bodies, as well as “diffused neuropiles” which lack clearly demarcated structures. K. Ito and T. Awasaki review the organization of the adult central brain and show how its complex architecture evolves from clonally related neural circuits. This book will be helpful to those who want to study brain development in the fly. As knowledge extracted from the Drosophila model has often proven to be of more general relevance, comparative aspects are included in most chapters. Therefore, this book should also be useful for researchers working on brain development in other organisms and on brain evolution, as well as for instructors and advanced students in the field of developmental neurobiology.
Development of the nervous system and establishment of complex neuronal networks require the conc... more Development of the nervous system and establishment of complex neuronal networks require the concerted activity of different signalling events and guidance cues, which include Netrins and their receptors. In Drosophila, two Netrins are expressed during embryogenesis by cells of the ventral midline and serve as attractant or repellent cues for navigating axons. We asked whether glial cells, which are also motile, are guided by similar cues to axons, and analysed the influence of Netrins and their receptors on glial cell migration during embryonic development. We show that in Netrin mutants, two distinct populations of glial cells are affected: longitudinal glia (LG) fail to migrate medially in the early stages of neurogenesis, whereas distinct embryonic peripheral glia (ePG) do not properly migrate laterally into the periphery. We further show that early Netrin-dependent guidance of LG requires expression of the receptor Frazzled (Fra) already in the precursor cell. At these early st...
The central nervous system is composed of segmental units (neuromeres), the size and complexity o... more The central nervous system is composed of segmental units (neuromeres), the size and complexity of which evolved in correspondence to their functional requirements. In Drosophila, neuromeres develop from populations of neural stem cells (neuroblasts) that delaminate from the early embryonic neuroectoderm in a stereotyped spatial and temporal pattern. Pattern units closely resemble the ground state and are rather invariant in thoracic (T1-T3) and anterior abdominal (A1-A7) segments of the embryonic ventral nerve cord. Here, we provide a comprehensive neuroblast map of the terminal abdominal neuromeres A8-A10, which exhibit a progressively derived character. Compared with thoracic and anterior abdominal segments, neuroblast numbers are reduced by 28% in A9 and 66% in A10 and are almost entirely absent in the posterior compartments of these segments. However, all neuroblasts formed exhibit serial homology to their counterparts in more anterior segments and are individually identifiable...
Locomotion relies on stable attachment of muscle fibres to their target sites, a process that all... more Locomotion relies on stable attachment of muscle fibres to their target sites, a process that allows for muscle contraction to generate movement. Here, we show that glide/gcm and glide2/gcm2, the fly glial cell determinants, are expressed in a subpopulation of embryonic tendon cells and required for their terminal differentiation. By using loss-of-function approaches, we show that in the absence of both genes, muscle attachment to tendon cells is altered, even though the molecular cascade induced by stripe, the tendon cell determinant, is normal. Moreover, we show that glide/gcm activates a new tendon cell gene independently of stripe. Finally, we show that segment polarity genes control the epidermal expression of glide/gcm and determine, within the segment,whether it induces glial or tendon cell-specific markers. Thus, under the control of positional cues, glide/gcm triggers a new molecular pathway involved in terminal tendon cell differentiation, which allows the establishment of...
Uploads