RAT TESTICULAR TESTIBUMIN IS IDENTICAL TO SULFATED GLYCOPROTEIN-1 (SGP-1) WHOSE MESSENGER-RNA EXPRESSION IN THE TESTIS IS AGE-DEPENDENT BUTNOT GERM CELL-DEPENDENT

Using sequential HPLC and capillary electrophoresis (CE), testibumin ( CMB-1) has been purified to apparent homogeneity from Sertoli cell-enr iched culture medium prepared from 20-day-old rat testes. N-Terminal a mino acid sequence analysis of the purified testibumin revealed a part ial sequence of NH2-XPVQDPKI. When this partial sequence was compared to existing protein database, it was shown that it is identical to a p reviously isolated Sertoli cell secretory protein, sulfated glycoprote in I (SGP-1). The fact that testibumin is equivalent to SGP-1 was furt her confirmed when its full-length cDNA was isolated and sequenced. St udies using quantitative PCR to examine the changes of steady-state mR NA 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 le vel was similar to the neonatal rat at 3 days of age. Depletion of ger m cells by a single dose of lonidamine, an antispermatogenic drug, did not induce an increase in testibumin (SGP-1) mRNA level indicating it s mRNA expression is not dependent on germ cells.