Differential gene expression in pre-implantation embryos from mouse oocytes injected with round spermatids or spermatozoa.
BACKGROUND
The use of immature male germ cells to fertilize human oocytes raises several questions. Spermatozoa are normally quiescent, but many genes are transcribed post-meiotically in round spermatids. This creates a novel situation for the oocyte. We have therefore explored the effects on early embryonic development of introducing a fully transcriptionally active round spermatid into the oocyte.


RESULTS
Following the micro-injection of spermatozoa or spermatids into mouse oocytes we have analysed the expression, at various times, of six genes in the resulting embryo. Spermatozoa and spermatids produced similar fertilization rates. Hprt was expressed in all embryos at all stages tested. Hsp70.1 was found normally during the 2-cell stage and repressed by the 4-cell stage in embryos from both spermatozoa and round spermatids. However, the amplitude of the signal was greatly reduced in 2-cell embryos from round spermatids. Smcy also showed a disturbed pattern of expression in embryos from round spermatids. Protamine 2, which is normally restricted to the spermatid stage, was expressed following fertilization with round spermatids, but was already repressed at the two pronuclei stage. Ube1Y, which is normally expressed post-meiotically and not during the post-implantatory development, was expressed up to the 2-cell stage in embryos from round spermatids only, and then repressed. Ube1X was also expressed up to the 2-cell stage, but in both embryo types.


CONCLUSIONS
We therefore suspect that in embryos fertilized with round spermatids, regulatory mechanisms for inhibiting the inappropriate transcription of male post-meiotically expressed genes are activated following fertilization, permitting the zygotic genome activation to occur, though with some disturbances.
Ziyyat
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Unité de Maturation Gamétique et Fécondation, INSERM and Institut Fédératif de Recherche sur les Cytokines, Clamart, France.
Lefèvre
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D000818:Animals; D015139:Blotting, Southern; D047108:Embryonic Development; D005260:Female; D005434:Flow Cytometry; D015870:Gene Expression; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics; D056466:Histone Demethylases; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics; D008025:Ligases / Q000235:genetics; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D008845:Microinjections; D009865:Oocytes / Q000378:metabolism*; D011247:Pregnancy; D011506:Proteins / Q000235:genetics; D015800:Protozoan Proteins / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020554:Sperm Injections, Intracytoplasmic; D013087:Spermatids; D013094:Spermatozoa; D044767:Ubiquitin-Protein Ligases; D015778:Minor Histocompatibility Antigens
D018840:HSP70 Heat-Shock Proteins; D056466:Histone Demethylases; D007041:Hypoxanthine Phosphoribosyltransferase; D008025:Ligases; D011506:Proteins; D015800:Protozoan Proteins; D012333:RNA, Messenger; D044767:Ubiquitin-Protein Ligases; C081884:heat-shock protein 70.1; C490659:Kdm5d protein, mouse; D015778:Minor Histocompatibility Antigens