RNA and membraneless organelles Membraneless compartments can form in cells through liquidliquid ... more RNA and membraneless organelles Membraneless compartments can form in cells through liquidliquid phase separation (see the Perspective by Polymenidou). But what prevents these cellular condensates from randomly fusing together? Using the RNA-binding protein (RBP) Whi3, Langdon et al. demonstrated that the secondary structure of different RNA components determines the distinct biophysical and biological properties of the two types of condensates that Whi3 forms. Several RBPs, such as FUS and TDP43, contain prion-like domains and are linked to neurodegenerative diseases. These RBPs are usually soluble in the nucleus but can form pathological aggregates in the cytoplasm. Maharana et al. showed that local RNA concentrations determine distinct phase separation behaviors in different subcellular locations. The higher RNA concentrations in the nucleus act as a buffer to prevent phase separation of RBPs; when mislocalized to the cytoplasm, lower RNA concentrations trigger aggregation. Scien...
Proceedings of the National Academy of Sciences, 2014
Significance In centrosomes, pericentriolar material (PCM) serves as the principle site for micro... more Significance In centrosomes, pericentriolar material (PCM) serves as the principle site for microtubule nucleation and anchoring. In Drosophila , the centrosomal protein spindle assembly defective-4 (Sas-4) scaffolds cytoplasmic PCM protein complexes via its N terminus and tethers them to centrioles via an unknown mechanism. By determining the crystal structure of Sas-4‘s C-terminal T complex protein 10 (TCP) domain and functional studies in Drosophila , human cells, and induced pluripotent stem cell-derived neural progenitors, we show that Sas-4 performs its tethering role via its TCP domain. Furthermore, point mutations within the TCP domain perturb PCM tethering while still allowing the protein to scaffold cytoplasmic PCM complexes. These studies provide insights into how Sas-4 proteins tether PCM complexes for the assembly of functional centrosomes.
Metaphase spindles are microtubule-based structures that use a multitude of proteins to modulate ... more Metaphase spindles are microtubule-based structures that use a multitude of proteins to modulate their morphology and function. Today, we understand many details of microtubule assembly, the role of microtubule-associated proteins, and the action of molecular motors. Ultimately, the challenge remains to understand how the collective behaviour of these nanometre-scale processes gives rise to a properly sized spindle on the micrometre scale. By systematically engineering the enzymatic activity of XMAP215, a processive microtubule polymerase, we show that Xenopus laevis spindle length increases linearly with microtubule growth velocity, whereas other parameters of spindle organization, such as microtubule density, lifetime and spindle shape, remain constant. We further show that mass balance can be used to link the global property of spindle size to individual microtubule dynamic parameters. We propose that spindle length is set by a balance of non-uniform nucleation and global microtubule disassembly in a liquid-crystal-like arrangement of microtubules.
Although programmed cell death (PCD) is extensively studied in multicellular organisms, in recent... more Although programmed cell death (PCD) is extensively studied in multicellular organisms, in recent years it has been shown that a unicellular organism, yeast Saccharomyces cerevisiae, also possesses death program(s). In particular, we have found that a high doses of yeast pheromone is a natural stimulus inducing PCD. Here, we show that the death cascades triggered by pheromone and by a drug amiodarone are very similar. We focused on the role of mitochondria during the pheromone/amiodarone-induced PCD. For the first time, a functional chain of the mitochondria-related events required for a particular case of yeast PCD has been revealed: an enhancement of mitochondrial respiration and of its energy coupling, a strong increase of mitochondrial membrane potential, both events triggered by the rise of cytoplasmic [Ca2+], a burst in generation of reactive oxygen species in center o of the respiratory chain complex III, mitochondrial thread-grain transition, and cytochrome c release from mi...
Microtubules are dynamic polymers that move stochastically between periods of growth and shrinkag... more Microtubules are dynamic polymers that move stochastically between periods of growth and shrinkage, a property known as dynamic instability. Here, to investigate the mechanisms regulating microtubule dynamics in Xenopus egg extracts, we have cloned the complementary DNA ...
RNA and membraneless organelles Membraneless compartments can form in cells through liquidliquid ... more RNA and membraneless organelles Membraneless compartments can form in cells through liquidliquid phase separation (see the Perspective by Polymenidou). But what prevents these cellular condensates from randomly fusing together? Using the RNA-binding protein (RBP) Whi3, Langdon et al. demonstrated that the secondary structure of different RNA components determines the distinct biophysical and biological properties of the two types of condensates that Whi3 forms. Several RBPs, such as FUS and TDP43, contain prion-like domains and are linked to neurodegenerative diseases. These RBPs are usually soluble in the nucleus but can form pathological aggregates in the cytoplasm. Maharana et al. showed that local RNA concentrations determine distinct phase separation behaviors in different subcellular locations. The higher RNA concentrations in the nucleus act as a buffer to prevent phase separation of RBPs; when mislocalized to the cytoplasm, lower RNA concentrations trigger aggregation. Scien...
Proceedings of the National Academy of Sciences, 2014
Significance In centrosomes, pericentriolar material (PCM) serves as the principle site for micro... more Significance In centrosomes, pericentriolar material (PCM) serves as the principle site for microtubule nucleation and anchoring. In Drosophila , the centrosomal protein spindle assembly defective-4 (Sas-4) scaffolds cytoplasmic PCM protein complexes via its N terminus and tethers them to centrioles via an unknown mechanism. By determining the crystal structure of Sas-4‘s C-terminal T complex protein 10 (TCP) domain and functional studies in Drosophila , human cells, and induced pluripotent stem cell-derived neural progenitors, we show that Sas-4 performs its tethering role via its TCP domain. Furthermore, point mutations within the TCP domain perturb PCM tethering while still allowing the protein to scaffold cytoplasmic PCM complexes. These studies provide insights into how Sas-4 proteins tether PCM complexes for the assembly of functional centrosomes.
Metaphase spindles are microtubule-based structures that use a multitude of proteins to modulate ... more Metaphase spindles are microtubule-based structures that use a multitude of proteins to modulate their morphology and function. Today, we understand many details of microtubule assembly, the role of microtubule-associated proteins, and the action of molecular motors. Ultimately, the challenge remains to understand how the collective behaviour of these nanometre-scale processes gives rise to a properly sized spindle on the micrometre scale. By systematically engineering the enzymatic activity of XMAP215, a processive microtubule polymerase, we show that Xenopus laevis spindle length increases linearly with microtubule growth velocity, whereas other parameters of spindle organization, such as microtubule density, lifetime and spindle shape, remain constant. We further show that mass balance can be used to link the global property of spindle size to individual microtubule dynamic parameters. We propose that spindle length is set by a balance of non-uniform nucleation and global microtubule disassembly in a liquid-crystal-like arrangement of microtubules.
Although programmed cell death (PCD) is extensively studied in multicellular organisms, in recent... more Although programmed cell death (PCD) is extensively studied in multicellular organisms, in recent years it has been shown that a unicellular organism, yeast Saccharomyces cerevisiae, also possesses death program(s). In particular, we have found that a high doses of yeast pheromone is a natural stimulus inducing PCD. Here, we show that the death cascades triggered by pheromone and by a drug amiodarone are very similar. We focused on the role of mitochondria during the pheromone/amiodarone-induced PCD. For the first time, a functional chain of the mitochondria-related events required for a particular case of yeast PCD has been revealed: an enhancement of mitochondrial respiration and of its energy coupling, a strong increase of mitochondrial membrane potential, both events triggered by the rise of cytoplasmic [Ca2+], a burst in generation of reactive oxygen species in center o of the respiratory chain complex III, mitochondrial thread-grain transition, and cytochrome c release from mi...
Microtubules are dynamic polymers that move stochastically between periods of growth and shrinkag... more Microtubules are dynamic polymers that move stochastically between periods of growth and shrinkage, a property known as dynamic instability. Here, to investigate the mechanisms regulating microtubule dynamics in Xenopus egg extracts, we have cloned the complementary DNA ...
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Papers by A. Pozniakovsky