Rat testicular testibumin is identical to sulfated glycoprotein-1 (SGP-1) whose mRNA expression in the testis is age- but not germ cell-dependent.

Using sequential HPLC and capillary electrophoresis (CE), testibumin (CMB-1) has been purified to apparent homogeneity from Sertoli cell-enriched culture medium prepared from 20-day-old rat testes. N-Terminal amino acid sequence analysis of the purified testibumin revealed a partial sequence of NH2-XPVQDPKI. When this partial sequence was compared to existing protein database, it was shown that it is identical to a previously isolated Sertoli cell secretory protein, sulfated glycoprotein I (SGP-1). The fact that testibumin is equivalent to SGP-1 was further confirmed when its full-length cDNA was isolated and sequenced. Studies using quantitative PCR to examine the changes of steady-state mRNA level of testibumin (SGP-1) in the rat testes between 3 and 60 days of age indicated that its mRNA increased rapidly after birth, peaked at 10-20 days, and declined rapidly where the adult testibumin mRNA level was similar to the neonatal rat at 3 days of age. Depletion of germ cells by a single dose of lonidamine, an antispermatogenic drug, did not induce an increase in testibumin (SGP-1) mRNA level indicating its mRNA expression is not dependent on germ cells.