21 research outputs found
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The onset of homologous chromosome pairing during Drosophila melanogaster embryogenesis.
We have determined the position within the nucleus of homologous sites of the histone gene cluster in Drosophila melanogaster using in situ hybridization and high-resolution, three-dimensional wide field fluorescence microscopy. A 4.8-kb biotinylated probe for the histone gene repeat, located approximately midway along the short arm of chromosome 2, was hybridized to whole-mount embryos in late syncytial and early cellular blastoderm stages. Our results show that the two homologous histone loci are distinct and separate through all stages of the cell cycle up to nuclear cycle 13. By dramatic contrast, the two homologous clusters were found to colocalize with high frequency during interphase of cycle 14. Concomitant with homolog pairing at cycle 14, both histone loci were also found to move from their position near the midline of the nucleus toward the apical side. This result suggests that coincident with the initiation of zygotic transcription, there is dramatic chromosome and nuclear reorganization between nuclear cycles 13 and 14
Recommended from our members
The onset of homologous chromosome pairing during Drosophila melanogaster embryogenesis.
We have determined the position within the nucleus of homologous sites of the histone gene cluster in Drosophila melanogaster using in situ hybridization and high-resolution, three-dimensional wide field fluorescence microscopy. A 4.8-kb biotinylated probe for the histone gene repeat, located approximately midway along the short arm of chromosome 2, was hybridized to whole-mount embryos in late syncytial and early cellular blastoderm stages. Our results show that the two homologous histone loci are distinct and separate through all stages of the cell cycle up to nuclear cycle 13. By dramatic contrast, the two homologous clusters were found to colocalize with high frequency during interphase of cycle 14. Concomitant with homolog pairing at cycle 14, both histone loci were also found to move from their position near the midline of the nucleus toward the apical side. This result suggests that coincident with the initiation of zygotic transcription, there is dramatic chromosome and nuclear reorganization between nuclear cycles 13 and 14
Structural and functional conservation at the boundaries of the chicken β-globin domain
We show that the 3′ boundary of the chicken β-globin locus bears striking structural similarities to the 5′ boundary. In erythroid cells a clear transition in DNase I sensitivity of chromatin at the 3′ end of the locus is observed, the location of this transition is marked by a constitutive DNase I hypersensitive site (HS), and DNA spanning this site has the enhancer-blocking capacity of an insulator. This HS contains a binding site for the transcription factor CTCF. As in the case of the 5′ insulator, the CTCF site is both necessary and sufficient for the enhancer-blocking activity of the 3′ boundary. The position of this insulator is consistent with our proposal that it may function to maintain the distinct regulatory programs of the globin genes and their closely appended 3′ neighbor, an odorant receptor gene. We conclude that both boundaries of the chicken β-globin domain are capable of playing functionally similar roles and that the same protein is a necessary component of the molecular mechanism through which these boundaries are defined