RESUMO
Meiosis is pivotal for sexual reproduction and fertility. Meiotic programmed DNA double-strand breaks (DSBs) initiate homologous recombination, ensuring faithful chromosome segregation and generation of gametes. However, few studies have focused on meiotic DSB formation in human reproduction. Here, we report four infertile siblings born to a consanguineous marriage, with three brothers suffering from non-obstructive azoospermia and one sister suffering from unexplained infertility with normal menstrual cycles and normal ovary sizes with follicular activity. An autosomal recessive mutation in TOP6BL was found co-segregating with infertility in this family. Investigation of one male patient revealed failure in programmed meiotic DSB formation and meiotic arrest prior to pachytene stage of prophase I. Mouse models carrying similar mutations to that in patients recapitulated the spermatogenic abnormalities of the patient. Pathogenicity of the mutation in the female patient was supported by observations in mice that meiotic programmed DSBs failed to form in mutant oocytes and oocyte maturation failure due to absence of meiotic recombination. Our study thus illustrates the phenotypical characteristics and the genotype-phenotype correlations of meiotic DSB formation failure in humans.
RESUMO
The genetic causes of oocyte meiotic deficiency (OMD), a form of primary infertility characterised by the production of immature oocytes, remain largely unexplored. Using whole exome sequencing, we found that 26% of a cohort of 23 subjects with OMD harboured the same homozygous nonsense pathogenic mutation in PATL2, a gene encoding a putative RNA-binding protein. Using Patl2 knockout mice, we confirmed that PATL2 deficiency disturbs oocyte maturation, since oocytes and zygotes exhibit morphological and developmental defects, respectively. PATL2's amphibian orthologue is involved in the regulation of oocyte mRNA as a partner of CPEB However, Patl2's expression profile throughout oocyte development in mice, alongside colocalisation experiments with Cpeb1, Msy2 and Ddx6 (three oocyte RNA regulators) suggest an original role for Patl2 in mammals. Accordingly, transcriptomic analysis of oocytes from WT and Patl2-/- animals demonstrated that in the absence of Patl2, expression levels of a select number of highly relevant genes involved in oocyte maturation and early embryonic development are deregulated. In conclusion, PATL2 is a novel actor of mammalian oocyte maturation whose invalidation causes OMD in humans.
Assuntos
Códon sem Sentido , Sequenciamento do Exoma/métodos , Perfilação da Expressão Gênica/métodos , Infertilidade/genética , Proteínas Nucleares/fisiologia , Oócitos/metabolismo , Proteínas de Ligação a RNA/fisiologia , Adulto , Animais , Estudos de Coortes , Feminino , Humanos , Meiose/genética , Camundongos Endogâmicos C57BL , Camundongos Knockout , Camundongos Transgênicos , Proteínas Nucleares/genética , Oócitos/citologia , Proteínas de Ligação a RNA/genética , Adulto JovemRESUMO
The oocyte's primary function is to be fertilised by a spermatozoon in order to create a viable embryo. Oocyte growth and development are initiated during embryogenesis and occur in parallel to follicular development. Factors produced by the oocyte bind to receptors on follicular cells, ensuring follicular development. Oocytes begin meiosis during foetal development and are arrested in prophase I by elevated levels of cyclic adenosine monophosphate (cAMP). Activation of mitogen-activated protein kinases triggers degradation of cAMP, allowing oocyte maturation to proceed. The production of progesterone and prostaglandins during the ovulation process ultimately activates proteases, whose action helps to release the oocyte into the Fallopian tube. Oocyte activation depends on fertilisation and is induced by changes in intracellular calcium levels. Dysregulation of these pathways is involved in the pathogenesis of several diseases including the syndrome of oocyte maturation failure.