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 spermiogenesis. Somatic type histones are displaced by transition proteins which are replaced themselves by protamines, the major nuclear proteins found in late spermatids and spermatozoa nuclei. Digoxigenin or Biotin labeled probes, coding respectively for human transition protein 1 (TP1) and protamine 1 (HP1), were used for double EM in situ hybridization. Immunodetection of hybrids with specific antibodies coupled to colloidal gold particles of different size (10 nm and 15 nm) was performed on the same preparations. Quantitative analysis of the nuclear and cytoplasmic labeling densities for the mRNAs coding for TP1 and HP1 showed the presence of transcripts in both the nucleus and cytoplasm of round spermatids until the elongation phase. Transcripts accumulated in the spermatid cytoplasm without any particular cellular compartmentalization. At the end of the spermatid elongation phase, the disappearing of TP1 and HP1 transcripts may be related to the arrest of transcriptional activity while the deposition of transition proteins and protamines successively occurs within spermatid nuclei.