Electron microscope study on spermatogenesis

Summary

The morphogenesis of chromosomes at early prophase of spermatocytes I is studied in three ortoptherian species: Grillus argentinus (Grillidae), Laplatacris dispar (Acrididae) and Blaptica dubia (Blaptidae).

The first chromosome component appearing at the beginning of meiosis is a thread (single elementary thread; S.E.T.) of low electron density measuring about 700 Å to 0.1 μ width. A group having the same width and integrated by three helically twisted ribbon-like components develops from S.E.T. and is called primary tripartite group, P.T.G. The three components are at first of the same width (about 200 Å) but the lateral arms progressively increase in thickness and in that way the group becomes coated by a layer of dense microfibrils supposed to be chromatin.

Late stages of prophase were not thoroughly investigated in this study, but many evidences were however found helping to identify synaptene stage. In accordance with these evidences each homologous chromosome is integrated by an axial component (tripartite groups) coated by chromatin.

The medial component of tripartite groups of Blaptica dubia is double and also shows multistranded regions which are called puffy regions.

A comparative optical and electron microscope study was made in order to better understand the above described process. This study includes the comparison of the thickness of chromosomes as measured in light and electron micrographs.

On the other hand, rubber models were made to illustrate the same process and pohotographs of these models are exhibited in the text.

The nuclear structure of early spermatids of the same species is also studied in this paper. It was found that Blaptica and Grillus early spermatids nuclei contain groups similar to those found at the beginning of prophase of spermatocyte I, with the only difference that in many cases composite groups, formed by fusion of the lateral arms of two or more than two single groups, were found.

The nuclear structure of late spermatids was also considered in this paper. Notwithstanding the study only aimed to point out that the pattern of organization of the spermatozoon chromatin greatly differs in the species examined.