Silver-stained synaptonemal complexes of human pachytene bivalents studied by light microscopy

The synaptonemal complex and meiotic recombination in humans: new approaches to old questions

Meiotic prophase serves as an arena for the interplay of two important cellular activities, meiotic recombination and synapsis of homologous chromosomes. Synapsis is mediated by the synaptonemal complex (SC), originally characterized as a structure linked to pairing of meiotic chromosomes (Moses (1958) J Biophys Biochem Cytol 4:633-638). In 1975, the first electron micrographs of human pachytene stage SCs were presented (Moses et al. (1975) Science 187:363-365) and over the next 15 years the importance of the SC to normal meiotic progression in human males and females was established (Jhanwar and Chaganti (1980) Hum Genet 54:405-408; Pathak and Elder (1980) Hum Genet 54:171-175; Solari (1980) Chromosoma 81:315-337; Speed (1984) Hum Genet 66:176-180; Wallace and Hulten (1985) Ann Hum Genet 49(Pt 3):215-226). Further, these studies made it clear that abnormalities in the assembly or maintenance of the SC were an important contributor to human infertility (Chaganti et al. (1980) Am J Hum Genet 32:833-848; Vidal et al. (1982) Hum Genet 60:301-304; Bojko (1983) Carlsberg Res Commun 48:285-305; Bojko (1985) Carlsberg Res Commun 50:43-72; Templado et al. (1984) Hum Genet 67:162-165; Navarro et al. (1986) Hum Reprod 1:523-527; Garcia et al. (1989) Hum Genet 2:147-53). However, the utility of these early studies was limited by lack of information on the structural composition of the SC and the identity of other SC-associated proteins. Fortunately, studies of the past 15 years have gone a long way toward remedying this problem. In this minireview, we highlight the most important of these advances as they pertain to human meiosis, focusing on temporal aspects of SC assembly, the relationship between the SC and meiotic recombination, and the contribution of SC abnormalities to human infertility.

A technique for light and electron microscopy of the synaptonemal complex of the mouse oocyte

A method is described for obtaining synaptonemal complex preparations from mouse pachytene oocytes for light and electron microscopic examination. A karyotype based on the whole complement of synaptonemal complexes of a pachytene oocyte as visualized by electron microscopy is presented.

Morphology and transcriptional activity of mouse oocyte chromosomes

Lampbrush chromosomes of growing amphibian oocytes carry thousands of lateral loops each of which consists of a chromatin fiber heavily encrusted with nascent ribonucleoprotein fibrils. These are believed to be responsible for the accumulation and maintenance of RNA transcripts found stored in the egg. In the case of mammalian oocytes, lampbrush chromosomes are most likely to occur during the major growth phase and also possibly during pachytene-early diplotene stages of meiosis. We have examined pachytene and early diplotene mouse oocyte chromosomes through the light microscope using sections of plastic-embedded material and air dried spreads stained with either silver nitrate or methyl green pyronin. Our results indicates that the projections radiating from the chromosomal axis are bundles of chromatin fibers rather than single fibers covered with an ribonucleoprotein matrix. These bundles may represent partially unfolded chromomeres. The axis itself could be partially dispersed revealing threads surrounding a fine linear element. -- Little is known about chromosome structure in growing mammalian oocytes, the stage when transcriptional activity is likely to be most rapid. In our preparations chromosomes at this stage appear as partially condensed fuzzy threads of relatively uniform width. In some cases, the fuzzy thread is seen to contain a dense linear core in the center. Thus, during the growth phase, the chromosomes retain a relatively condensed axis, a characteristic of meiotic chromosomes in general. RNA-containing material is found diffusely spread within the nucleus but not specifically associated with the chromosomes. Electron microscopic analysis of spread chromatin from growing oocytes demonstrates that most transcription units possess only one or two nascent ribonucleoprotein fibrils while a few have more. These and other published data indicate that mouse oocytes do not have true lampbrush chromosomes at any stage of their development.

A light microscopic study of the development and behaviour of the synaptonemal complex in spermatocytes of the mouse

A method is presented for the sequential analysis of male meiosis using hydroxyurea (HU). HU produces a gap in the spermatogenic line. The front of surviving cells behind the gap was examined day by day using silverstained whole mount spreads on glass slides. With this method it was possible to study the development and behaviour of the synaptonemal complex (SC) in mouse spermatocytes by the light microscope. At zygotene no unpaired axial elements could be seen. Unpaired axial elements were found to be specific for the diplotene stage. The axes of the XY pair could be recognized from late zygotene up to diplotene.