Jean-Pierre Dadoune

Transcription in haploid male germ cells.

Major modifications in chromatin organization occur in spermatid nuclei, resulting in a high degree of DNA packaging within the spermatozoon head. However, before arrest of transcription during midspermiogenesis, high levels of mRNA are found in round spermatids. Some transcripts are the product of genes expressed ubiquitously, whereas some are generated from male germ cell-specific gene homologs of somatic cell genes. Others are transcript variants derived from genes with expression regulated in a testis-specific fashion. The haploid genome of spermatids also initiates the transcription of testis-specific genes. Various general transcription factors, distinct promoter elements, and specific transcription factors are involved in transcriptional regulation. After meiosis, spermatids are genetically but not phenotypically different, because of transcript and protein sharing through cytoplasmic bridges connecting spermatids of the same generation. Interestingly, different types of mRNAs accumulate in the sperm cell nucleus, raising the question of their origin and of a possible role after fertilization.

Ultrastructural localization of rDNA and rRNA by in situ hybridization in the nucleolus of human spermatids

The ultrastructural localization of rDNA and rRNA within the nucleolus of human spermatids was investigated by in situ hybridization at steps 1 and 2. Two different digoxigenin-labeled human probes from the rRNA transcription unit were used. Identification of hybrids was performed with immunogold techniques. Comparative observations in the Sertoli cell nucleolus as controls revealed that rDNA was predominantly visualized in the threads of the dense fibrillar component, while rRNA was detected over both the fibrillar component and the granular component. Whithin the nucleolus of round spermatids in the same sections of seminiferous tubules, rDNA labeling was localized over the spherical or stranded dense fibrillar components. rRNA labeling was found not only over these components but also in the adjacent nucleoplasm rich in ribonucleoprotein particles. These results are consistent with the view that the round spermatid nucleolus is transcriptionally active.

Cytochemical variations in the nucleolus during spermiogenesis in man and monkey

SummaryThe fine structure, nature and fate of the components of the nucleolus were studied in young (steps 1, 2), intermediate (steps 3, 4, 5) and mature spermatids (steps 6, 7, 8) of man and monkey, by use of several cytochemical techniques (alcoholic PTA; sodium tungstate; EDTA; HAPTA; nuclease-gold complexes; NOR silver staining). As controls, comparative ultrastructural and cytochemical observations of the nucleolus in spermatids and Sertoli cells were made in the same sections of seminiferous tubules. In the young spermatids of the two species studied, the nucleolar masses exhibited identical features. Segregation of the nucleolar components took place in the nuclei of step 1 spermatids. No typical fibrillar center was observed. In spermatids at steps 1 and 2, the nucleolar masses appeared to be made up of two fibrillar components of equal density, one spherule-shaped, the other forming cords, both surrounded by clusters of 15–20 nm-diameter granules. Alcoholic PTA and sodium tungstate yielded a selective positive contrast of the two fibrillar components whereas EDTA and RNase-gold reacted with the peripheral granular material. Treatment with RNase-gold and DNase-gold complexes resulted in preferential labeling at the periphery of the fibrillar components. After NOR silver staining, numerous small silver grains were localized over the fibrillar cords, suggesting the persistence of specific acidic non-histone proteins. On the contrary, the spherule was never stained. In intermediate spermatids, when the nucleolar components were dissociated, scattered clusters of granules stained by EDTA and HAPTA remained in the entire nucleoplasm. Nucleolar disintegration was accompanied by dispersion of argyrophilic material. In mature spermatids granular material revealed by PTA and silver staining methods was found in the nuclear pockets bounded by the redundant nuclear envelope.

Cytoskeleton and morphogenesis of the spermatozoan: actin, calmodulin

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