Expression of mRNA and protein of nucleoproteins during human spermiogenesis.

The most important event determining the nuclear status of sperm cells is the replacement of histones by protamines, which are the basic nuclear proteins of mature spermatozoa. A first step in this exchange is the displacement of histones by transition proteins (TP). Our study demonstrates, for the first time, the sequential expression of the testis-specific histone (H1t) and the transition proteins (TP1 and TP2) during normal human spermatogenesis. H1t mRNA could only be detected in the cytoplasm of mid and late pachytene spermatocytes. Concomitant with the onset of H1t transcription, the H1t protein appeared in the nuclei of pachytene spermatocytes and remain as a nuclear protein constituent up to step 5 spermatids. While transition protein 1 gene TNP-1 mRNA was present in spermatids from step 2 to early step 4, the TP1 protein occured, with temporal delay, in the nuclei of step 3 and step 4 spermatids. The TP2 protein was observed in the nuclei of spermatids from step 1 to step 5. The transition protein 2 gene TNP-2 mRNA was only detected by reverse transcription-polymerase chain reaction, but not on paraffin sections. These data demonstrate a strong temporal association between H1t gene transcription and synthesis of the H1t protein. Since the TP1 protein appeared with temporal delay we can assume that the corresponding TNP-1 mRNA is translationally delayed.