pachytene

After 24 h the morphology of the pachytene cells is greatly reduced.

The technique used in the preparation of these human pachytene cells is that of Luciani et al.

Spread pachytene oocytes prepared by this method from the mouse (Figure 9a) and human (Figure 9b) are shown.

Ovaries from aborted human fetuses have been shown to have cells in the pachytene stage during weeks 16-23 of gestation (25).

These are highly refractile bodies seen only at the pachytene stage, and which correspond to the No. 9 C-band region seen at metaphase.

The mouse pachytene spread is photographed at LM level: the human spread is taken in the EM.

This "tripartite structure" is seen during the pachytene stage of the first meiotic prophase, both in males and in females during gametogenesis.

It is one of the final phases of genetic recombination, which occurs during prophase I of meiosis (pachytene) in a process called synapsis.

BOULE is expressed later, in the cytoplasm of pachytene spermatocytes [ 5 ] .

Previous to the pachytene stage, during leptonema, the lateral elements begin to form and they initiate and complete their pairing during the zygotene stage.

Th resolution with pachytene chromosomes is claimed to be better than that obtained with high resolution banded somatic chromosomes (16,17).

A striking correspondence between chromomeres and mitotic G-bands has been observed, and complete pachytene karyotypes in man (12) and the mouse (13) have been produced.

Extended pachytene chromosomes prepared by the techniques described in Section 2.6 have been used for the localization of genes by in situ hybridization techniques (16,17).

Localization of Spo11 across synapsed, pachytene chromosomes of mice also suggests that Spo11 has an additional role, after it catalyzes recombination, in meiosis [ 25 ] .

The chiasmata become visible during the diplotene stage of prophase I of meiosis, but the actual "crossing-over" of genetic material is thought to occur during the previous pachytene stage.

At late pachytene, each bivalent exhibits a linear sequence of compacted regions of chromatin or "chromomeres" which vary in number, size and sequence for each chromosome in the complement.

The mouse oocyte in the dictyate (prolonged diplotene) stage actively repairs DNA damage, whereas DNA repair is not detectable in the pre-dictyate (leptotene, zygotene and pachytene) stages of meiosis.

In support of this possibility, Spo11 of mice colocalizes extensively along homologously synapsed chromosomes during pachytene and dissociates when the homologs segregate from one-another during anaphase of MI [ 25 ] .

In the human female, meiosis commences towards the end of the first trimester of fetal development and, with increasing gestational age, more and more cells enter the prophase stages of leptotene, zygotene and pachytene.

Special air-drying techniques using extended room temperature hypotonic treatments, or shorter hypotonic treatments at higher temperatures, have been devised for the production of extended pachytene chromosomes which can be used for mapping of individual bivalents (10-13).

A primary processing pathway is suggested to be the only pathway used to produce pachytene piRNAs; in this mechanism, piRNA precursors are transcribed resulting in piRNAs with a tendency to target 5' uridines.