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

Régis E Meyer,Ounissa Aït-Ahmed,Michèle Capri,Roland Rosset,Michèle Delaage

doi:10.1186/1471-2156-11-104

Abstract

BackgroundSexual 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.ResultsWe 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.ConclusionsWe 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.

Highlights

Sexual reproduction relies on two key events: formation of cells with a haploid genome and restoration of diploidy after fertilization
Identification and characterization of the first yem-alpha mutant allele Drosophila yem-alpha was identified in a search for genes that are differentially expressed in the female germ line [14,18,19]
Because in Drosophila the formation of the first mitotic spindle of the zygote is dependent on the centrosomes provided by the sperm cell [21]yem1 female sterile phenotype cannot be attributed to fertilization defects

Summary

Introduction

Sexual reproduction relies on two key events: formation of cells with a haploid genome (the gametes) and restoration of diploidy after fertilization. The yem mutant females exhibited disrupted chromosome behavior in the first meiotic division and produced very low numbers of viable progeny. 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. In meiosis, a single round of DNA replication is followed by two successive divisions: meiosis I that segregates the chromosomes with Another significant difference is that recombination during prophase I between non-sister chromatids links the homologues in a structure termed a bivalent. Drosophila females have to deal with the necessity to segregate both exchange (chiasmate) and non exchange (achiasmate) chromosomes [4]

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Results

Conclusion