CHARACTERIZATION OF A PREMEIOTIC GERM CELL-SPECIFIC CYTOPLASMIC PROTEIN ENCODED BY STRA8, A NOVEL RETINOIC ACID-RESPONSIVE GENE

The full-length cDNA corresponding to Stra8, a novel gene inducible by retinoic acid (RA) in P19 embryonal carcinoma cells, has been isolate d and shown to encode a 45-kD protein. Both Stra8 mRNA and protein wer e induced in cells treated by all-trans and 9-cis retinoic acids. Two- dimensional gel analysis and dephosphorylation experiments revealed th at the two stereoisomers of RA differentially regulate the phosphoryla tion status of the Stra8 protein, which was shown to exist in differen tly phosphorylated forms. Subcellular fractionation and immunocytochem istry studies showed that the Stra8 protein is cytoplasmic. During mou se embryogenesis, Stra8 expression was restricted to the male developi ng gonads, and in adult mice, the expression of Stra8 was restricted t o the premeiotic germ cells. Thus, Stra8 protein may play a role in th e premeiotic phase of spermatogenesis.