Sex Chromosome Pairing Mediated by Euchromatic Homology in Drosophila Male Meiosis. 2020

Christopher A Hylton, and Katie Hansen, and Andrew Bourgeois, and John E Tomkiel Dean
Department of Biology, University of North Carolina, Greensboro, North Carolina 27402 cahylton@uncg.edu jetomkie@uncg.edu.

Diploid germline cells must undergo two consecutive meiotic divisions before differentiating as haploid sex cells. During meiosis I, homologs pair and remain conjoined until segregation at anaphase. Drosophila melanogaster spermatocytes are unique in that the canonical events of meiosis I including synaptonemal complex formation, double-strand DNA breaks, and chiasmata are absent. Sex chromosomes pair at intergenic spacer sequences within the ribosomal DNA (rDNA). Autosomes pair at numerous euchromatic homologies, but not at heterochromatin, suggesting that pairing may be limited to specific sequences. However, previous work generated from genetic segregation assays or observations of late prophase I/prometaphase I chromosome associations fail to differentiate pairing from maintenance of pairing (conjunction). Here, we separately examined the capability of X euchromatin to pair and conjoin using an rDNA-deficient X and a series of Dp(1;Y) chromosomes. Genetic assays showed that duplicated X euchromatin can substitute for endogenous rDNA pairing sites. Segregation was not proportional to homology length, and pairing could be mapped to nonoverlapping sequences within a single Dp(1;Y) Using fluorescence in situ hybridization to early prophase I spermatocytes, we showed that pairing occurred with high fidelity at all homologies tested. Pairing was unaffected by the presence of X rDNA, nor could it be explained by rDNA magnification. By comparing genetic and cytological data, we determined that centromere proximal pairings were best at segregation. Segregation was dependent on the conjunction protein Stromalin in Meiosis, while the autosomal-specific Teflon was dispensable. Overall, our results suggest that pairing may occur at all homologies, but there may be sequence or positional requirements for conjunction.

UI MeSH Term Description Entries
D008297 Male Males
D008540 Meiosis A type of CELL NUCLEUS division, occurring during maturation of the GERM CELLS. Two successive cell nucleus divisions following a single chromosome duplication (S PHASE) result in daughter cells with half the number of CHROMOSOMES as the parent cells. M Phase, Meiotic,Meiotic M Phase,M Phases, Meiotic,Meioses,Meiotic M Phases,Phase, Meiotic M,Phases, Meiotic M
D002503 Centromere The clear constricted portion of the chromosome at which the chromatids are joined and by which the chromosome is attached to the spindle during cell division. Centromeres
D004275 DNA, Ribosomal DNA sequences encoding RIBOSOMAL RNA and the segments of DNA separating the individual ribosomal RNA genes, referred to as RIBOSOMAL SPACER DNA. Ribosomal DNA,rDNA
D004331 Drosophila melanogaster A species of fruit fly frequently used in genetics because of the large size of its chromosomes. D. melanogaster,Drosophila melanogasters,melanogaster, Drosophila
D006570 Heterochromatin The portion of chromosome material that remains condensed and is transcriptionally inactive during INTERPHASE. Heterochromatins
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D012730 Sex Chromosomes The homologous chromosomes that are dissimilar in the heterogametic sex. There are the X CHROMOSOME, the Y CHROMOSOME, and the W, Z chromosomes (in animals in which the female is the heterogametic sex (the silkworm moth Bombyx mori, for example)). In such cases the W chromosome is the female-determining and the male is ZZ. (From King & Stansfield, A Dictionary of Genetics, 4th ed) Gonosomes,Chromosome, Sex,Chromosomes, Sex,Gonosome,Sex Chromosome
D013090 Spermatocytes Male germ cells derived from SPERMATOGONIA. The euploid primary spermatocytes undergo MEIOSIS and give rise to the haploid secondary spermatocytes which in turn give rise to SPERMATIDS. Spermiocytes,Spermatocyte,Spermiocyte
D014960 X Chromosome The female sex chromosome, being the differential sex chromosome carried by half the male gametes and all female gametes in human and other male-heterogametic species. Chromosome, X,Chromosomes, X,X Chromosomes

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