Developmental expression of Y-box protein 1 mRNA and alternatively splicedY-box protein 3 mRNAs in spermatogenic cells in mice

Y-box proteins bind DNA and RNA and are characterized by a cold shock domai n and a carboxyl-terminus containing clusters of aromatic and basic residue s that alternate with clusters of acidic residues. Y-box proteins 1 and 3 i n mouse testis were cloned here by 3' rapid amplification of cDNA ends (RAC E) using a degenerate primer. Northern blots and reverse transcription-poly merase chain reaction (RT-PCR) established that the levels of Y-box protein 1 and 3 mRNAs are regulated individually: (i) Y-box protein 1 mRNA is stro ngly expressed in kidney, whereas Y-box protein 3 mRNA is strongly expresse d in heart and muscle; (ii) Y-box protein 1 and 3 mRNAs are weakly expresse d in early prepubertal testis and strongly expressed in pachytene spermatoc ytes, round spermatids, and elongated spermatids; and (iii) prepubertal tes tes and meiotic and haploid spermatogenic cells express two alternatively s pliced Y-box protein 3 mRNAs encoding isoforms with different carboxyl term ini, whereas somatic tissues primarily express one form. Sucrose gradients reveal that similar to 27% of both Y-box protein 3 mRNAs are translationall y active in adult testis. in conclusion, spermatogenic cells in mice expres s five isoforms of Y-box proteins including Y-box protein 1, and two isofor ms each of Y-box proteins 2 and 3. This multiplicity is intriguing because Y-box proteins are thought to activate transcription and repress translatio n in spermatogenic cells.