Expression of mannose 6-phosphate receptor messenger ribonucleic acids in mouse spermatogenic and Sertoli cells.

ABSTRACT Spermatogenic and Sertoli cells isolated from the mouse synthesize different proportions of the two mannose 6-phosphatereceptors (MPR) during overnight culture periods (O'Brien et al., Endocrinology 1989; 125:2973). To determine the relativeexpression of MPR mRNAs in these cells, poly(A) + RNAs were examined by Northern blot analysis using cDNA probes specificfor the cation-independent (CI) and cation-dependent (CD) MPRs. A single CI-MPR transcript, -10 kb in size, was present inall tissues and cell types examined. Like the CI-MPR protein, this transcript was more abundant in Sertoli cells than in sperma-togenic cells isolated from adult testes. The CD-MPR is the predominant MPR synthesized by pachytene spermatocytes or roundspermatids. Multiple CD-MPR transcripts were detected in these cells, including a 2.4-kb CD-MPR mRNA that was indistinguish-able from CD-MPR transcripts in somatic tissues and Sertoli cells. Smaller CD-MPR mRNAs of -1.4 and 1.6 kb were prominentin pachytene spermatocytes and round spermatids, respectively, but were faint or undetectable in somatic tissues. These smallerCD-MPR mRNAs did not hybridize with an 0.9-kb restriction fragment derived from the CD-MPR 3' untranslated region (UTR),suggesting that alternate polyadenylation signals are used to produce multiple CD-MPR transcripts in spermatogenic cells. Whenpoly(A) tracts were selectively removed from germ cell RNAs by ribonuclease H treatment, identical 1.3-kb CD-MPR mRNAswere detected in pachytene spermatocytes and round spermatids, indicating that the size difference between the 1.4- and 1.6-kb transcripts is due to variations in poly(A) tail length. These alterations in the 3' UTR of the CD-MPR transcripts may affectmRNA stability or translation during spermatogenesis.