DDX3X, the X homologue of AZFa gene DDX3Y, expresses a complex pattern of transcript variants only in the male germ line.

DDX3X, the functional X homologue of the major AZFa gene, DDX3Y, belongs to the highly conserved PL10-subfamily of DEAD-box RNA helicase genes which are functionally conserved from yeast to man. They are mainly involved in cell cycle control and translation initiation control of gene transcripts with long 5'UTR extensions containing complex secondary structures. Interestingly, in humans both gene copies were found to be expressed at different phases of human spermatogenesis. Whereas DDX3Y transcripts are translated only in premeiotic male germ cells, the DDX3X protein is expressed only in postmeiotic spermatids. In this study, we found that the major class of DDX3X transcripts in human testis become activated first after meiosis and at a specific core promoter not active in somatic tissues and not present upstream of the DDX3Y homologue. Two alternative 5'UTR transcript lengths are subsequently produced by an additional testis-specific 5'UTR splicing event. Both transcripts are mainly processed for polyadenylation in their proximal 3'UTR. A minor transcript class starting at the same male germ line-specific core promoter produces primary transcripts with an extremely long 3'UTR (∼ 17 kb), which is subsequently spliced at distinct sites resulting in six short 3'UTR splice variants (I-VI). Comparative analyses of the DDX3X transcripts in mouse and primates revealed that this complex pattern of male germ line-specific transcript variants first evolved in primates. Our data thus suggest complex translational control mechanism(s) for the human DDX3X gene locus functioning only in the male germ line and resulting in expression of its protein only in the postmeiotic spermatids.

Rauschendorf MA ，Zimmer J ，Ohnmacht C ，Vogt PH ... -  《-》

Complex transcriptional control of the AZFa gene DDX3Y in human testis.

The human DEAD-box Y (DBY) RNA helicase (aka DDX3Y) gene is thought to be the major azoospermia factor a (AZFa) gene in proximal Yq11. Men with its deletion display no somatic pathologies, but suffer from complete absence of germ cells. Accordingly, DDX3Y protein is expressed only in the germline in spermatogonia, although the transcripts were found in many tissues. Here, we show the complex transcriptional control of a testis-specific DDX3Y transcript class with initiation at different sites upstream of the gene's open reading frame (5'Untranslated Region; UTR) and with polyadenylation in their proximal 3'UTR. The most distal transcriptional start site (TSS; ∼1 kb upstream) was mapped in MSY2, a Y-specific minisatellite. As this testis-specific 5'UTR was subsequently processed by three alternative splicing events, it has been tentatively designated 'exon-T'(estis). The MSY2 sequence unit was also found upstream of the mouse Ddx3y gene. However, only after its tandem amplification on the Y chromosome of Platyrrhini (new world monkeys) and Catarrhini (old world monkeys) did MSY2 become part of a novel distal promoter for DDX3Y expression in testis tissue and provides a second transcriptional start site (T-TSS-II) in Catarrhini. We therefore suggest that the development of a novel distal DDX3Y promoter in primates, which is activated only in testis tissue, is probably part of the gene's germline translation control.

Rauschendorf MA ，Zimmer J ，Hanstein R ，Dickemann C ，Vogt PH ... -  《-》

AZFa Y gene, DDX3Y, evolved novel testis transcript variants in primates with proximal 3´UTR polyadenylation for germ cell specific translation.

Translational control is a major level of gene expression regulation in the male germ line. DDX3Y located in the AZFa region of the human Y chromosome encodes a conserved RNA helicase important for translational control at the G1-S phase of the cell cycle. In human, DDX3Y protein is expressed only in premeiotic male germ cells. In primates, DDX3Y evolved a second promoter producing novel testis-specific transcripts. Here, we show primate species-specific use of alternative polyadenylation (APA) sites for these testis-specific DDX3Y transcript variants. They have evolved subsequently in the 3´UTRs of the primates´ DDX3Y transcripts. Whereas a distal APA site (PAS4) is still used for polyadenylation of most DDX3Y testis transcripts in Callithrix jacchus; two proximal APAs (PAS1; PAS2) are used predominantly in Macaca mulatta, in Pan trogloydates and in human. This shift corresponds with a significant increase of DDX3Y protein expression in the macaque testis tissue. In chimpanzee and human, shift to predominant use of the most proximal APA site (PAS1) is associated with translation of these DDX3Y transcripts in only premeiotic male germ cells. We therefore assume evolution of a positive selection process for functional DDX3Y testis transcripts in these primates which increase their stability and translation efficiency to promote its cell cycle balancing function in the human male germ line.

Vogt PH ，Rauschendorf MA ，Zimmer J ，Drummer C ，Behr R ... -  《-》

Translational control of the AZFa gene DDX3Y by 5'UTR exon-T extension.

The human DEAD-box Y (DBY) RNA helicase (aka DDX3Y) gene is thought to be the major azoospermia factor a (AZFa) gene in proximal Yq11. Although it is transcribed in many tissues, the protein is expressed only in spermatogonia. In this study, we demonstrate that this translational control mechanism is probably germ cell-specific because of its association with expression of a distinct class of DDX3Y testis transcripts present only in pre- and post-meiotic male germ cells. They are initiated from a second distal DDX3Y promoter domain at two distinct start sites in the gene's 5' untranslated region (UTR) exon-T sequence. With the aid of an EGFP-3xFLAG reporter cassette cloned downstream of DDX3Y minigenes containing exons 1-4 and two different exon-T extensions, we discovered that DDX3Y translation is influenced by the presence of several ATG triplets located in exon-T, thus upstream of the main translational ATG start codon in exon 1. Strong translational repression of the DDX3Y minigene transcripts was observed when they contained the longest exon-T sequence with five upstream ATG triplets (uATGs). The potential formation of complex distinct stem-loop structures serve here as additional repressor element. Only minor translational attenuation was seen for the DDX3Y minigene transcripts when containing the shortest exon-T sequence, that is, starting at first transcriptional start site (coined 'T-TSS-I'). It was completely released after its single uATG was abolished by mutation. As we found DDX3Y transcripts with the longest exon-T sequence predominantly in spermatids, our results suggest that the amount of DDX3Y protein in pre-meiotic germ cells and its absence in post-meiotic germ cells are tightly controlled by the different extensions of exon-T in this germ cell-specific DDX3Y transcript class.

Jaroszynski L ，Zimmer J ，Fietz D ，Bergmann M ，Kliesch S ，Vogt PH ... -  《-》

Molecular characterization of the DDX3Y gene and its homologs in cattle.

DDX3Y (also known as DBY) is a member of the DEAD box protein family, which is involved in ATP-dependent RNA unwinding, needed in a variety of cellular processes including splicing, ribosome biogenesis and RNA degradation. In the human, DDX3Y is located in the AZFa interval in the Y chromosome. Deletion of the AZFa region has been shown to disrupt spermatogenesis, causing subfertility and infertility in otherwise healthy men. Here, we report the characterization of the bovine (b) DDX3Y gene and its homologs DDX3X and PL10. We found 2 transcripts for the bDDX3Y (bDDX3Y-L and -S), which correspond to the long and short transcripts of the human DDX3Y and mouse Ddx3y gene. The 2 transcripts are identical except for a 3-bp (AGT) insertion at the position of nt 2025 and an expanded 3'UTR (nt 2155-2769) in bDDX3Y-L. The bDDX3Y-S encodes a peptide of 660 amino acids (aa), while the bDDX3Y-L encodes a peptide of 661 aa as the result of an additional serine (S) insertion at the position of aa 634. Both bDDX3Y isoforms contain the conserved DEAD-box motif. The bDDX3Y is composed of 17 exons. The homologous gene on the X chromosome, bDDX3X, is highly conserved to the Y-copy at mRNA (83%) and protein (88%) levels as well as in the genomic structure. The autosomal copy, bPL10, mapped on BTA15, is a processed pseudogene with a similarity of 88.1% to bDDX3Y and 93.7% to bDDX3X mRNA, suggesting that PL10 is a retroposon of DDX3X. RT-PCR analyses showed that bDDX3Y-L, -S, bDDX3X and bPL10 were all widely expressed with predominant expression in testis and brain. Testicular section in situ hybridization revealed that sense and anti-sense RNAs of bDDX3Y-L, -S, and bDDX3X were expressed in interstitial cells. These results together with the finding that the pseudogene bPL10 is transcriptionally active in this study provide a basis for further investigating the DDX3 gene function in spermatogenesis, male fertility and gene evolution in mammals.

Liu WS ，Wang A ，Yang Y ，Chang TC ，Landrito E ，Yasue H ... -  《-》