Electron microscopic in situ hybridization study of simultaneous expression of TNP1 and PRM1 genes in human spermatids

Nuclear changes in the basic nucleoprotein complement occur during human sp ermiogenesis. Somatic type histones are displaced by transition proteins wh ich are replaced themselves by protamines, the major nuclear proteins found in late spermatids and spermatozoa nuclei. Digoxigenin or Biotin labeled p robes, coding respectively for human transition protein 1 (TP1) and protami ne 1 (HP1), were used for double EM in situ hybridization. Immunodetection of hybrids with specific antibodies coupled to colloidal gold particles of different size (10nm and 15nm) was performed on the same preparations. Quan titative analysis of the nuclear and cytoplasmic labeling densities for the mRNAs coding for TP1 and HP1 showed the presence of transcripts in both th e nucleus and cytoplasm of round spermatids until the elongation phase. Tra nscripts accumulated in the spermatid cytoplasm without any particular cell ular compartmentalization. At the end of the spermatid elongation phase, th e disappearing of TP1 and HP1 transcripts may be related to the arrest of t ranscriptional activity while the deposition of transition proteins and pro tamines successively occurs within spermatid nuclei.