TRANSCRIPTIONAL ANALYSIS OF THE CANDIDATE SPERMATOGENESIS GENE UBE1Y AND OF THE CLOSELY-RELATED UBE1X SHOWS THAT THEY ARE COEXPRESSED IN SPERMATOGONIA AND SPERMATIDS BUT ARE REPRESSED IN PACHYTENE SPERMATOCYTES

Ube1y is a Y-linked gene transcribed in the testis, which maps to a re gion of the mouse Y required for normal spermatogonial proliferation. Ube1y, together with a ubiquitously expressed homologue on the X chrom osome (Ube1x), encodes ubiquitin-activating enzyme E1, an enzyme essen tial for eukaryotic cell proliferation. Ube1y is thus a strong candida te for the Y function in spermatogonial proliferation Using probes spe cific for the two genes, we have used Northern analysis and RNase prot ection to assess transcript levels throughout testis development and, by using germ cell-deficient XXSxr'' testes and purified cell fraction s, we have defined the testicular cell types in which transcription oc curs. Ube1y transcripts are already detectable in the fetal testis at 12.5 dpc, with higher levels at 14.5 dpc and then falling to low level s by the time of birth. Postnatally levels rise sharply, peaking at 10 dpp. Analysis of XXSxr(a) testes indicates that the bulk of. the Ube1 y transcription is in germ cells. The analysis of purified cell fracti ons shows that X- and Y-encoded transcripts are present in A spermatog onia, both are at very low levels (or perhaps absent) in pachytene spe rmatocytes and then return to high levels in round spermatids. The rea ctivation of transcription in round spermatids implies a requirement f or the ubiquitination pathway at this time. The presence of Ube1x tran scripts in A spermatogonia raises the question as to why Ube1y transcr ipts are required. This question is discussed in relation to the sperm atogenic failure in XSxr(b)O mice which are deleted for Ube1y and it i s argued that Ube1y serves to increase UBE1 production at a time of hi gh demand. Ube1y transcripts were also detected in XXY and XY ovaries. (C) 1996 Academic Press, Inc.