Nucleoli, nucleolar chromosomes and ribosomal genes in the human spermatocyte.

The formation and development of nucleoli and their connections with the nucleolar chromosomes were studied in human spermatocytes using electron microscopy, silver staining of nucleolus organizer regions (NORs), high resolution autoradiography and in situ hybridization in order to localize rRNA genes and their transcription in the different stages of meiotic prophase I. At leptotene, new nucleoli were formed, consisting of a fibrillar centre surrounded by a cap of dense fibrillar component. Following [3H]uridine uptake, label was found only over the dense fibrillar component.

Ribosomal DNA is located and transcribed in the dense fibrillar component of human Sertoli cell nucleoli.

The distribution of rDNA and the uptake of tritiated uridine was investigated in nucleoli of human Sertoli cells. The nucleolar components in these cells are spatially arranged in a highly ordered and invariable way and can be recognized in both light and electron microscopy. The pattern of distribution of rDNA and the pattern of uridine uptake in these nucleoli correspond to the distribution of the dense fibrillar component but cannot be correlated to the shape and size of the fibrillar centers in these cells.

Yq deletion and failure of spermatogenesis.

The spermatogenesis of a sterile male carrying a Y long arm deletion was analyzed by meiotic techniques and by light and electron microscopy on testicular biopsies. R-, Q- and C- banding techniques have shown that the Y long arm deletion included the entire heterochromatin and a part of the euchromatic region, with breakpoint between q11.21 and q11.

Random acrocentric bivalent associations in human pachytene spermatocytes. Molecular implications in the occurrence of Robertsonian translocations.

Acrocentric bivalent associations were studied in 232 human male germ cells at pachytene in order to understand better the preferential involvement of chromosomes 13, 14, and 21 in Robertsonian translocations. The tendency of each acrocentric bivalent to associate with another was not correlated with NOR activity, as measured by silver staining. Good agreement was noticed between their ability to associate and the amount of satellite DNA in human acrocentric chromosomes.

The association of the nucleolus and the short arm of acrocentric chromosomes with the XY pair in human spermatocytes: its possible role in facilitating sex-chromosome acrocentric translocations.

Sex vesicle-nucleolus association was observed in 12% of zygotene and pachytene human spermatocytes using Giemsa and NOR-silver stained preparations. The silver-positive area of the nucleolus, corresponding to the nucleolus organizer (NOR), was usually close to the XY pair. C-banding frequently showed the terminal chromomere, formed by the condensed short arm of an acrocentric bivalent, attached to the sex vesicle.

Distribution of fibrillar centers and silver-stained components in the nucleolus of human Sertoli cells.

The nucleolus of the human Sertoli cell consistently showed three distinct, spontaneously segregated parts: 1. one or two large, silver-positive fibrillar centers; 2. strands of dense fibrillar component continuous with the dense cords surrounding the fibrillar center.

Structural basis for Robertsonian translocations in man: association of ribosomal genes in the nucleolar fibrillar center in meiotic spermatocytes and oocytes.

The spatial relationships of acrocentric chromosomes were studied during prophase I of meiosis in human oocytes and spermatocytes by using cytogenetic techniques, electron microscopy, and in situ hybridization. Ultrastructural investigations revealed an ordered arrangement of nucleolar bivalents at the zygotene and pachytene stages. The end of the bivalent corresponding to the cytological satellite was consistently attached to the nuclear envelope.

[Do male germ cells begin meiosis during fetal life?].

The existence of a preleptotene chromosome condensation and decondensation stage occuring between the last premeiotic interphase and the leptotene stage was described in numberous plants. This stage was also reported in the human fetal oocyte and in various animals (rabbit, sheep, mouse). A similar process of chromosome condensation was described in the human foetal testis, but in this latter, the decondensation phase leading to leptotene was never observed.

[Oocyte meiosis in a trisomy 18 fetus. Behavior of the supernumerary chromosome and identification of the 18 bivalent].

Associations of the three n degrees 18 chromosomes were studied in a trisomy 18 fetus (the chromosomal constitution of which had been identified by amniocentesis). The three classes of associations observed were those observed in other trisomic organisms:trivalent, trivalent presenting an important asynaptic region, and bivalent accompanied by a univalent. In addition, the sequence was established of chromomeres, the number of which varied from 18 to 23 depending on the degree of chromosome contraction.

The meiotic behavior of triploidy in a human 69,XXX fetus.

Meiotic studies were made on the fetal ovaries of a triploid fetus, 69,XXX. The association modalities of the three chromosomes in human triploidy are the same as those described in several plant species; i.e.

Pachytene mapping of the C9 and acrocentric bivalents in the human oocyte.

Provisional maps are presented for all acrocentric bivalents and bivalent 9, according to their chromomere patterns at pachytene in the human oocyte. Each G band is subdivided into several sub-bands whose numbers varies according to the degree of chromosomal compacting. Chromomere number and sequence are in basic agreement with those observed in late prophase mitotic chromosomes.

Preleptotene chromosome condensation stage in human foetal and neonatal testes.

A preleptotene stage of chromosome condensation analogous to that already described in various plants and in the oocytes of several animal species has been observed in the human foetal testis. Contrary to what has been previously described, this stage in the testis is not followed by decondensation leading to leptotene filaments. This observation underlines the problem of the precise significance of this stage and its relation to initiation of meiosis.

Meiosis of trisomy 21 in the human pachytene oocyte. Behaviour of the supernumerary chromosome, identification of chromomere sequence and numerous sub-bands.

Association modalities of the three 21 chromosomes were studied during pachytene in three trisomy 21 fetuses whose chromosomal constitution was identified following amniocentesis. -- Three classes of images were observed: a trivalent, a trivalent presenting an important asynaptic region of the long arm, and a bivalent accompanied by a univalent. Such behaviour is analagous to that observed in all trisomic organisms.

Constitutive heterochromatin and micronucleoli in the human oocyte at the diplotene stage.

In the diplotene stage of the human oocyte, the processes of elaboration of the nucleolar material are amplified. The principal nucleoli are more voluminous but their relations with the secondary constrictions and the satellites of the D and G chromosomes are not modified. Numerous micronucleoli, frequently to the number of 15-20 this stage.