EXPRESSION OF MANNOSE 6-PHOSPHATE RECEPTOR MESSENGER RIBONUCLEIC-ACIDS IN MOUSE SPERMATOGENIC AND SERTOLI CELLS

Spermatogenic and sertoli cells isolated from the mouse synthesize dif ferent proportions of the two mannose 6-phosphate receptors (MPR) duri ng overnight culture periods (O'Brien et al., Endocrinology 1989; 125: 2973). To determine the relative expression of MPR mRNAs in these cell s, poly(A)(+) RNAs were examined by Northern blot analysis using cDNA probes specific for the cation-independent (CI) and cation-dependent ( CD) MPRs. A single CI-MPR transcript, similar to 10 kb in size, was pr esent in all tissues and cell types examined. Like the CI-MPR protein, this transcript was more abundant in Sertoli cells than in spermatoge nic cells isolated from adult testes. The CD-MPR is the predominant MP R synthesized by pachytene spermatocytes or round spermatids. Multiple CD-MPR transcripts were detected in these cells, including a 2.4-kb C D-MPR mRNA that was indistinguishable from CD-MPR transcripts in somat ic tissues and Sertoli cells. Smaller CD-MPR mRNAs of similar to 1.4 a nd 1.6 kb were prominent in pachytene spermatocytes and round spermati ds, respectively, but were faint or undetectable in somatic tissues. T hese smaller CD-MPR mRNAs did not hybridize with an 0.9-kb restriction fragment derived from the CD-MPR 3' untranslated region (UTR), sugges ting that alternate polyadenylation signals are used to produce multip le CD-MPR transcripts in spermatogenic cells. When poly(A) tracts were selectively removed from germ cell RNAs by ribonuclease H treatment, identical 1.3-kb CD-MPR mRNAs were 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 leng th. These alterations in the 3' UTR of the CD-MPR transcripts may affe ct mRNA stability or translation during spermatogenesis.