The VL30 family is a retroviruslike gene family with no apparent nucleic acid homology to any kno... more The VL30 family is a retroviruslike gene family with no apparent nucleic acid homology to any known retrovirus. Over 100 copies of VL30 DNA elements are dispersed throughout the mouse genome. Sequence analysis of the VL30 long terminal repeat (LTR) units showed that, whereas the LTR units of a given VL30 DNA element were almost identical, the LTR units associated with distinct members of the family were very different from one another. Comparison of the LTR sequences possessed by two particular VL30 DNA elements revealed a pattern of extensively homologous DNA segments adjacent to only distantly related DNA sequences. With the aid of sub-LTR probes, it was shown that a certain LTR is composed of both U5 sequences that are abundantly present in all species of the genus Mus and a U3 region detected only in Mus musculus. In addition, we isolated a VL30 DNA element in which the LTR units were replaced by the LTR units of an apparently novel retroviruslike family. These findings suggest ...
In the course of structural analysis of VL30 DNA elements, a recombinant retroviruslike element w... more In the course of structural analysis of VL30 DNA elements, a recombinant retroviruslike element was encountered that contained non-VL30 long terminal repeats (LTRs) flanking internal VL30 sequences. With the aid of this novel LTR sequence probe, we cloned several DNA elements that were apparently members of a new retroviruslike family. A particular DNA element representative of this family (designated GLN) was characterized. It was approximately 8 kilobase pairs long and contained LTRs that are 430 base pairs long. It possessed an unusual primer-binding site sequence that corresponds to tRNAGln and a polypurine tract primer that is adjacent to the 3' LTR. The nucleotide sequences of the LTRs and their adjacent regions (which together housed all cis-acting retroviral functions) were different from those of known retroviruses and retroviruslike families. The comparison of three different GLN LTR sequences revealed a marked heterogeneity of U3 sequences relative to the homogeneity ...
The mouse genome contains over 100 copies of a dispersed gene family known as "virus-like&qu... more The mouse genome contains over 100 copies of a dispersed gene family known as "virus-like" genes encoding 30S RNA (VL30). Although they do not share nucleotide sequence homology with known retroviruses, these genetic elements are distinguished by several "retrovirus-like" features, notably, the capacity of the 30S RNA transcripts of these genes to be encapsidated by c-type virions and the transmissibility of VL30 information to other cells via pseudovirion infection. Using VL30 DNA units, cloned from the BALB/c mouse embryonic gene library, we have recently shown that VL30 DNA units share basic structural features with retrovirus proviruses. To shed light on the relatedness of VL30 information to endogenous proviruses and possibly other genetic elements, we extended our previous studies concerning genomic distribution patterns of VL30 elements and patterns of sequence heterogeneity among VL30 units. The following observations were made: (i) VL30 units were distri...
Recombination between viral and cellular genes can give rise to new strains of retroviruses. For ... more Recombination between viral and cellular genes can give rise to new strains of retroviruses. For example, Rous-associated virus 61 (RAV-61) is a recombinant between the Bryan high-titer strain of Rous sarcoma virus (RSV) and normal pheasant DNA. Nucleic acid hybridization techniques were used to study the genome of RAV-61 and another RAV with subgroup F specificity (RAV-F) obtained by passage of RSV-RAV-0 in cells from a ring-necked pheasant embryo. The nucleotide sequences acquired by these two independent isolates of RAV-F that were not shared with the parental virus comprised 20 to 25% of the RAV-F genomes and were indistinguishable by nucleic acid hybridization. (In addition, RAV-F genomes had another set of nucleotide sequences that were homologous to some pheasant nucleotide sequences and also were present in the parental viruses.) A specific complementary DNA, containing only nucleotide sequences complementary to those acquired by RAV-61 through recombination, was prepared. T...
ferT is a testis-specific transcript of FER encoding a truncated version of the potential tyrosin... more ferT is a testis-specific transcript of FER encoding a truncated version of the potential tyrosine kinase. Using in situ hybridization analysis, we found that ferT was transiently expressed during spermatogenesis and that expression was restricted to spermatocytes at the pachytene stage of meiotic prophase. This pattern of expression is unprecedented by other tyrosine kinases and suggests a role for ferT in a particular stage of spermatogenesis.
Proceedings of the National Academy of Sciences, 2016
Significance Generation of new neurons is maintained in the adult hippocampus throughout life. Th... more Significance Generation of new neurons is maintained in the adult hippocampus throughout life. The process, which is driven by an exhaustible reservoir of neuronal stem cells (NSCs), greatly declines with age, however. We show that even a short, episodic exposure to the angiogenic factor VEGF and a resultant ramification/rejuvenation of the vasculature within the stem cell microenvironment (“niche”) is sufficient for neurogenesis to proceed at a markedly elevated rate for months later without accelerating the rate of NSC depletion. Importantly, this manipulation culminates in marked attenuation of age-dependent neurogenic decline. Long-term neurogenic enhancement via VEGF preconditioning was found to be associated with extensive NSC morphological remodeling resembling a “juvenile” pattern of NSC and blood vessel engagements.
Features that distinguish tumor vasculatures from normal blood vessels are sought to enable the d... more Features that distinguish tumor vasculatures from normal blood vessels are sought to enable the destruction of preformed tumor vessels. We show that blood vessels in both a xenografted tumor and primary human tumors contain a sizable fraction of immature blood vessels that have not yet recruited periendothelial cells. These immature vessels are selectively obliterated as a consequence of vascular endothelial growth factor (VEGF) withdrawal. In a xenografted glioma, the selective vulnerability of immature vessels to VEGF loss was demonstrated by downregulating VEGF transgene expression using a tetracycline-regulated expression system. In human prostate cancer, the constitutive production of VEGF by the glandular epithelium was suppressed as a consequence of androgen-ablation therapy. VEGF loss led, in turn, to selective apoptosis of endothelial cells in vessels devoid of periendothelial cells. These results suggest that the unique dependence on VEGF of blood vessels lacking periendot...
Proceedings of the National Academy of Sciences, 1997
We have recently shown that VEGF functions as a survival factor for newly formed vessels during d... more We have recently shown that VEGF functions as a survival factor for newly formed vessels during developmental neovascularization, but is not required for maintenance of mature vessels. Reasoning that expanding tumors contain a significant fraction of newly formed and remodeling vessels, we examined whether abrupt withdrawal of VEGF will result in regression of preformed tumor vessels. Using a tetracycline-regulated VEGF expression system in xenografted C6 glioma cells, we showed that shutting off VEGF production leads to detachment of endothelial cells from the walls of preformed vessels and their subsequent death by apoptosis. Vascular collapse then leads to hemorrhages and extensive tumor necrosis. These results suggest that enforced withdrawal of vascular survival factors can be applied to target preformed tumor vasculature in established tumors. The system was also used to examine phenotypes resulting from over-expression of VEGF. When expression of the transfected VEGF cDNA was...
Proceedings of the National Academy of Sciences, 2007
A key energy-saving adaptation to chronic hypoxia that enables cardiomyocytes to withstand severe... more A key energy-saving adaptation to chronic hypoxia that enables cardiomyocytes to withstand severe ischemic insults is hibernation, i.e., a reversible arrest of contractile function. Whereas hibernating cardiomyocytes represent the critical reserve of dysfunctional cells that can be potentially rescued, a lack of a suitable animal model has hampered insights on this medically important condition. We developed a transgenic mouse system for conditional induction of long-term hibernation and a system to rescue hibernating cardiomyocytes at will. Via myocardium-specific induction (and, in turn, deinduction) of a VEGF-sequestering soluble receptor, we show that VEGF is indispensable for adjusting the coronary vasculature to match increased oxygen consumption and exploit this finding to generate a hypoperfused heart. Importantly, ensuing ischemia is tunable to a level at which large cohorts of cardiomyocytes are driven to enter a hibernation mode, without cardiac cell death. Relieving the ...
Proceedings of the National Academy of Sciences, 2011
Neurons, astrocytes, and blood vessels are organized in functional “neurovascular units” in which... more Neurons, astrocytes, and blood vessels are organized in functional “neurovascular units” in which the vasculature can impact neuronal activity and, in turn, dynamically adjust to its change. Here we explored different mechanisms by which VEGF, a pleiotropic factor known to possess multiple activities vis-à-vis blood vessels and neurons, may affect adult neurogenesis and cognition. Conditional transgenic systems were used to reversibly overexpress VEGF or block endogenous VEGF in the hippocampus of adult mice. Importantly, this was done in settings that allowed the uncoupling of VEGF-promoted angiogenesis, neurogenesis, and memory. VEGF overexpression was found to augment all three processes, whereas VEGF blockade impaired memory without reducing hippocampal perfusion or neurogenesis. Pertinent to the general debate regarding the relative contribution of adult neurogenesis to memory, we found that memory gain by VEGF overexpression and memory impairment by VEGF blockade were already ...
The VL30 family is a retroviruslike gene family with no apparent nucleic acid homology to any kno... more The VL30 family is a retroviruslike gene family with no apparent nucleic acid homology to any known retrovirus. Over 100 copies of VL30 DNA elements are dispersed throughout the mouse genome. Sequence analysis of the VL30 long terminal repeat (LTR) units showed that, whereas the LTR units of a given VL30 DNA element were almost identical, the LTR units associated with distinct members of the family were very different from one another. Comparison of the LTR sequences possessed by two particular VL30 DNA elements revealed a pattern of extensively homologous DNA segments adjacent to only distantly related DNA sequences. With the aid of sub-LTR probes, it was shown that a certain LTR is composed of both U5 sequences that are abundantly present in all species of the genus Mus and a U3 region detected only in Mus musculus. In addition, we isolated a VL30 DNA element in which the LTR units were replaced by the LTR units of an apparently novel retroviruslike family. These findings suggest ...
In the course of structural analysis of VL30 DNA elements, a recombinant retroviruslike element w... more In the course of structural analysis of VL30 DNA elements, a recombinant retroviruslike element was encountered that contained non-VL30 long terminal repeats (LTRs) flanking internal VL30 sequences. With the aid of this novel LTR sequence probe, we cloned several DNA elements that were apparently members of a new retroviruslike family. A particular DNA element representative of this family (designated GLN) was characterized. It was approximately 8 kilobase pairs long and contained LTRs that are 430 base pairs long. It possessed an unusual primer-binding site sequence that corresponds to tRNAGln and a polypurine tract primer that is adjacent to the 3' LTR. The nucleotide sequences of the LTRs and their adjacent regions (which together housed all cis-acting retroviral functions) were different from those of known retroviruses and retroviruslike families. The comparison of three different GLN LTR sequences revealed a marked heterogeneity of U3 sequences relative to the homogeneity ...
The mouse genome contains over 100 copies of a dispersed gene family known as "virus-like&qu... more The mouse genome contains over 100 copies of a dispersed gene family known as "virus-like" genes encoding 30S RNA (VL30). Although they do not share nucleotide sequence homology with known retroviruses, these genetic elements are distinguished by several "retrovirus-like" features, notably, the capacity of the 30S RNA transcripts of these genes to be encapsidated by c-type virions and the transmissibility of VL30 information to other cells via pseudovirion infection. Using VL30 DNA units, cloned from the BALB/c mouse embryonic gene library, we have recently shown that VL30 DNA units share basic structural features with retrovirus proviruses. To shed light on the relatedness of VL30 information to endogenous proviruses and possibly other genetic elements, we extended our previous studies concerning genomic distribution patterns of VL30 elements and patterns of sequence heterogeneity among VL30 units. The following observations were made: (i) VL30 units were distri...
Recombination between viral and cellular genes can give rise to new strains of retroviruses. For ... more Recombination between viral and cellular genes can give rise to new strains of retroviruses. For example, Rous-associated virus 61 (RAV-61) is a recombinant between the Bryan high-titer strain of Rous sarcoma virus (RSV) and normal pheasant DNA. Nucleic acid hybridization techniques were used to study the genome of RAV-61 and another RAV with subgroup F specificity (RAV-F) obtained by passage of RSV-RAV-0 in cells from a ring-necked pheasant embryo. The nucleotide sequences acquired by these two independent isolates of RAV-F that were not shared with the parental virus comprised 20 to 25% of the RAV-F genomes and were indistinguishable by nucleic acid hybridization. (In addition, RAV-F genomes had another set of nucleotide sequences that were homologous to some pheasant nucleotide sequences and also were present in the parental viruses.) A specific complementary DNA, containing only nucleotide sequences complementary to those acquired by RAV-61 through recombination, was prepared. T...
ferT is a testis-specific transcript of FER encoding a truncated version of the potential tyrosin... more ferT is a testis-specific transcript of FER encoding a truncated version of the potential tyrosine kinase. Using in situ hybridization analysis, we found that ferT was transiently expressed during spermatogenesis and that expression was restricted to spermatocytes at the pachytene stage of meiotic prophase. This pattern of expression is unprecedented by other tyrosine kinases and suggests a role for ferT in a particular stage of spermatogenesis.
Proceedings of the National Academy of Sciences, 2016
Significance Generation of new neurons is maintained in the adult hippocampus throughout life. Th... more Significance Generation of new neurons is maintained in the adult hippocampus throughout life. The process, which is driven by an exhaustible reservoir of neuronal stem cells (NSCs), greatly declines with age, however. We show that even a short, episodic exposure to the angiogenic factor VEGF and a resultant ramification/rejuvenation of the vasculature within the stem cell microenvironment (“niche”) is sufficient for neurogenesis to proceed at a markedly elevated rate for months later without accelerating the rate of NSC depletion. Importantly, this manipulation culminates in marked attenuation of age-dependent neurogenic decline. Long-term neurogenic enhancement via VEGF preconditioning was found to be associated with extensive NSC morphological remodeling resembling a “juvenile” pattern of NSC and blood vessel engagements.
Features that distinguish tumor vasculatures from normal blood vessels are sought to enable the d... more Features that distinguish tumor vasculatures from normal blood vessels are sought to enable the destruction of preformed tumor vessels. We show that blood vessels in both a xenografted tumor and primary human tumors contain a sizable fraction of immature blood vessels that have not yet recruited periendothelial cells. These immature vessels are selectively obliterated as a consequence of vascular endothelial growth factor (VEGF) withdrawal. In a xenografted glioma, the selective vulnerability of immature vessels to VEGF loss was demonstrated by downregulating VEGF transgene expression using a tetracycline-regulated expression system. In human prostate cancer, the constitutive production of VEGF by the glandular epithelium was suppressed as a consequence of androgen-ablation therapy. VEGF loss led, in turn, to selective apoptosis of endothelial cells in vessels devoid of periendothelial cells. These results suggest that the unique dependence on VEGF of blood vessels lacking periendot...
Proceedings of the National Academy of Sciences, 1997
We have recently shown that VEGF functions as a survival factor for newly formed vessels during d... more We have recently shown that VEGF functions as a survival factor for newly formed vessels during developmental neovascularization, but is not required for maintenance of mature vessels. Reasoning that expanding tumors contain a significant fraction of newly formed and remodeling vessels, we examined whether abrupt withdrawal of VEGF will result in regression of preformed tumor vessels. Using a tetracycline-regulated VEGF expression system in xenografted C6 glioma cells, we showed that shutting off VEGF production leads to detachment of endothelial cells from the walls of preformed vessels and their subsequent death by apoptosis. Vascular collapse then leads to hemorrhages and extensive tumor necrosis. These results suggest that enforced withdrawal of vascular survival factors can be applied to target preformed tumor vasculature in established tumors. The system was also used to examine phenotypes resulting from over-expression of VEGF. When expression of the transfected VEGF cDNA was...
Proceedings of the National Academy of Sciences, 2007
A key energy-saving adaptation to chronic hypoxia that enables cardiomyocytes to withstand severe... more A key energy-saving adaptation to chronic hypoxia that enables cardiomyocytes to withstand severe ischemic insults is hibernation, i.e., a reversible arrest of contractile function. Whereas hibernating cardiomyocytes represent the critical reserve of dysfunctional cells that can be potentially rescued, a lack of a suitable animal model has hampered insights on this medically important condition. We developed a transgenic mouse system for conditional induction of long-term hibernation and a system to rescue hibernating cardiomyocytes at will. Via myocardium-specific induction (and, in turn, deinduction) of a VEGF-sequestering soluble receptor, we show that VEGF is indispensable for adjusting the coronary vasculature to match increased oxygen consumption and exploit this finding to generate a hypoperfused heart. Importantly, ensuing ischemia is tunable to a level at which large cohorts of cardiomyocytes are driven to enter a hibernation mode, without cardiac cell death. Relieving the ...
Proceedings of the National Academy of Sciences, 2011
Neurons, astrocytes, and blood vessels are organized in functional “neurovascular units” in which... more Neurons, astrocytes, and blood vessels are organized in functional “neurovascular units” in which the vasculature can impact neuronal activity and, in turn, dynamically adjust to its change. Here we explored different mechanisms by which VEGF, a pleiotropic factor known to possess multiple activities vis-à-vis blood vessels and neurons, may affect adult neurogenesis and cognition. Conditional transgenic systems were used to reversibly overexpress VEGF or block endogenous VEGF in the hippocampus of adult mice. Importantly, this was done in settings that allowed the uncoupling of VEGF-promoted angiogenesis, neurogenesis, and memory. VEGF overexpression was found to augment all three processes, whereas VEGF blockade impaired memory without reducing hippocampal perfusion or neurogenesis. Pertinent to the general debate regarding the relative contribution of adult neurogenesis to memory, we found that memory gain by VEGF overexpression and memory impairment by VEGF blockade were already ...
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Papers by E. Keshet