To determine whether male germ cells contain specific storage sites for poly(A)+ RNAs, in situ hybridizations were performed with sections of rat testis and a [3H]polyuridylic acid probe. The highest levels of poly(A)+ RNA were found in spermatocytes and round spermatids, while lower levels of poly(A)+ RNA were detected in spermatogonia, elongated spermatids, Sertoli cells, myoid cells, fibroblasts, macrophages, and Leydig cells. No poly(A)+ RNA was detected in residual bodies of elongated spermatids. At stages IX-XI of the seminiferous cycle, the nuclei and cytoplasm of pachytene spermatocytes contained approximately equal amounts of poly(A)+ RNA, suggesting nuclear RNA storage and/or a reduced processing rate of mRNA precursors at this stage of germ cell differentiation. To examine the distribution of poly(A)+ RNAs in subcellular components of testicular cells, electron microscope radioautography was used. In germ cells and Sertoli cells, poly(A)+ RNA was often seen free in the cytoplasm or associated with the endoplasmic reticulum and was only occasionally found associated with mitochondria, lysosomes, lipid inclusions, and axonemes. As previously reported for the mRNAs of transition protein 1 and protamine 1 [Morales et al., J Cell Sci 1991; 100: 119–131], no compartmentalization of poly(A)+ RNAs was detected in the cytoplasm of round and elongated spermatids. No poly(A)+ RNA was detected in association with the radial body and in most sections, the chromatoid body did not contain any significant amounts of poly(A)+ RNA.

Author notes

Supported by a grant from the MRC to C.R.M. and N.I.H. grant (HD28832) to N.B.H. C.R.M. is a fellow of the Fonds de la recherche en santé du Québec.