A NOVEL, TESTIS-SPECIFIC MEMBER OF THE CELLULAR LIPOPHILIC TRANSPORT PROTEIN SUPERFAMILY, DEDUCED FROM A COMPLIMENTARY DEOXYRIBONUCLEIC-ACID CLONE

A novel member of the cellular lipophilic transport protein superfamil y was identified after an antiserum raised against cellular retinoic a cid-binding protein (CRABP) was found also to contain antibodies again st another 15-kDa protein present in the cytosol of pubertal and adult rat testis. These antibodies were used to screen a rat testis cDNA ex pression library and isolate a 561-bp clone containing a full open rea ding frame from which the sequence of a novel 132 amino acid protein w as deduced. The protein has 58% amino acid sequence identity to bovine myelin P2, 58% identity to murine adipocyte lipid-binding protein, an d 40% identity to rat CRABP. Although the endogenous ligand has not ye t been identified, conservation of residues involved in the binding of carboxylate groups suggests that the ligand is a fatty acid or an aci dic retinoid. Tissue-specific expression was examined by Northern anal ysis and immunolocalization and appears to be restricted to late germ cells within the testis and epididymis. Immunostaining was first detec table in mid-pachytene spermatocytes and increased in intensity as the se cells progressed to elongated spermatids, suggesting that this test is lipid-binding protein has a specific role in sperm development.