Mouse Testes Contain Two Size Classes of Actin mRNA That Are Differentially Expressed During Spermatogenesis

Abstract

Using several actin isotype-specific cDNA probes, we found actin mRNA of two size classes, 2.1 and 1.5 kilobases (kb), in extracts of polyadenylated and nonpolyadenylated RNA from sexually mature CD-1 mouse testes. Although the 2.1-kb sequence was present in both meiotic and postmeiotic testicular cell types, it decreased manyfold in late haploid cells. The 1.5-kb actin sequence was not detectable in meiotic pachytene spermatocytes (or in liver or kidney cells), but was present in round and elongating spermatids and residual bodies. To differentiate between the β- and γ-actin mRNAs, we isolated a cDNA, pMGA, containing the 3′ untranslated region of a mouse cytoplasmic actin that has homology to the 3′ untranslated region of a human γ-actin cDNA but not to the 3′ untranslated regions of human α-, β-, or cardiac actins. Dot blot hybridizations with pMGA detected high levels of presumptive γ-actin mRNA in pachytene spermatocytes and round spermatids, with lower amounts found in elongating spermatids. Hybridization with the 3′ untranslated region of a rat β-actin probe revealed that round spermatids contained higher levels of β-actin mRNA than did pachytene spermatocytes or residual bodies. Both probes hybridized to the 2.1-kb actin mRNA but failed to hybridize to the 1.5-kb mRNA.