A single mutation results in diploid gamete formation and parthenogenesis in a Drosophila yemanuclein-alpha meiosis I defective mutant.

BACKGROUND: Sexual reproduction relies on two key events: formation of cells with a haploid genome (the gametes) and restoration of diploidy after fertilization. Therefore the underlying mechanisms must have been evolutionary linked and there is a need for evidence that could support such a model. RESULTS: We describe the identification and the characterization of yem1, the first yem-alpha mutant allele (V478E), which to some extent affects diploidy reduction and its restoration. Yem-alpha is a member of the Ubinuclein/HPC2 family of proteins that have recently been implicated in playing roles in chromatin remodeling in concert with HIRA histone chaperone. The yem1 mutant females exhibited disrupted chromosome behavior in the first meiotic division and produced very low numbers of viable progeny. Unexpectedly these progeny did not display paternal chromosome markers, suggesting that they developed from diploid gametes that underwent gynogenesis, a form of parthenogenesis that requires fertilization. CONCLUSIONS: We focus here on the analysis of the meiotic defects exhibited by yem1 oocytes that could account for the formation of diploid gametes. Our results suggest that yem1 affects chromosome segregation presumably by affecting kinetochores function in the first meiotic division. This work paves the way to further investigations on the evolution of the mechanisms that support sexual reproduction.

Grunge, related to human Atrophin-like proteins, has multiple functions in Drosophila development.

We have carried out a genetic screen designed to isolate regulators of teashirt expression. One of these regulators is the Grunge gene, which encodes a protein with motifs found in human arginine-glutamic acid dipeptide repeat, Metastasis-associated-like and Atrophin-1 proteins. Grunge is the only Atrophin-like protein in Drosophila, whereas several exist in humans. We provide evidence that Grunge is required for the proper regulation of teashirt but also has multiple activities in fly development. First, Grunge is crucial for correct segmentation during embryogenesis via a failure in the repression of at least four segmentation genes known to regulate teashirt. Second, Grunge acts positively to regulate teashirt expression in proximoventral parts of the leg. Grunge has other regulatory functions in the leg, including the patterning of ventral parts along the entire proximodistal axis and the proper spacing of bristles in all regions.