A CDNA selection approach to isolate Y-linked genes expressed in testis

Statistical analysis has revealed that 2-7% of couples remain childless at the end of their reproductive life. In about half of these cases, the problem lies with the male partner. It is expected that genes expressed in the testis, and involved in spermatogenesis, will occur on the Y-chromosome. This view has been confirmed with the isolation of the Y-linked RBMY, TSPY and DAZ genes, deletions of which appear to be present in cases of oligo- and azoospermia. In an effort to identify further Y-linked, testis-expressed genes, a cDNA selection library that was made by selecting testis cDNA with 1,000 Y- linked cosmid clones, was screened for Y-specific cDNAs. Screening with vector sequences and Y-linked repeat sequences, led to the elimination of more than 80% of the clones. Of the remaining 731 potential cDNA clones, sequencing revealed 79 clones with homology to several sequences in the database, including Y-linked and testis related sequences. A number of sequences isolated from the cDNA selection library appeared to represent novel members of two gene families and they were further investigated. These studies revealed that the TTY2 gene, published by Lahn and Page (1997), is member of a large Y-linked multicopy gene family with an estimated number of 26 copies. Two members of this gene family, termed ml 13d 10 and ml22a3 TTY2-like genes, were further investigated, as representatives of the TTY2 gene family. One more cDNA clone, termed 22d8, showed homology with several ESTs of unknown function and a 3.4kb cDNA that was recently released in the database (Feb. 2000) from a testis cDNA library. Investigation of this potential gene, revealed that either the whole, or part of it, is present in several chromosomal locations, including the Y chromosome and that it is ubiquitously expressed in many tissues, including testis