Recombination nodules and synaptonemal complex in recombination-defective females of Drosophila melanogaster

Abstract

The cytological effects of mutant alleles of the mei-9, mei-218, and mei-41 loci during prophase I have been examined by electron microscopy. None of these mutants affect synaptonemal complex structure, continuity, or temporal behavior. Both the precondition-defective mutants mei-218 and mei-41 affect both number and morphology of spherical recombination nodules and apparently affect at least the numbers of ellipsoidal recombination nodules, whereas in the exchange-defective mutant mei-9 the numbers and morphologies of both ellipsoidal and spherical recombination nodules are normal. The parallel effects of mei-218 and mei-41 on meiotic recombination and on recombination nodules indicate that spherical recombination nodules at least mark the site of exchange events; the effects of these mutants on nodule morphology suggest that the nodule performs an active role in the recombination process. The nodule phenotype of mei-9 indicates that spherical nodules are present, and presumably functioning, well before the concluding stages of the recombination event. The parallel effects of all 3 mutants on ellipsoidal and spherical nodules indicate that these are indeed related structures but does not ellucidate the nature of the relationship. It is suggested that all aspects of meiotic recombination are under the aegis of recombination nodules.

Crossing over analysis at pachytene in man

“…[6][7][8][9] If MLH1 is indeed a component of late RNs, then our study is the first in which a full complement of recombination nodules have been identified in human spermatocytes (reviewed by Ashley). 10 During complex reconstruction of serially sectioned human spermatocytes Holm and Rasmussen 38 failed to find a full set of 50 late RNs in a single nucleus, with a mean of 35 late RNs found in mid-pachytene nuclei.…”

“…[3][4][5] Electron microscope (EM) studies of pachytene meiocytes have revealed the presence of SC associated granules whose positions show good correspondence with sites of chiasmata, known as late recombination nodules (late RNs). [6][7][8][9] Late recombination nodules are with traditional staining techniques both beyond the resolution of the light microscope and apparently ephemeral structures with no reports of the observation of a full complement in humans. 10 In a recent immunofluorescence study of the distribution of the DNA mis-match repair protein M1h1 in microspread mouse prophase meiocytes, 11 it was concluded that this protein localises to sites of crossing over as a possible component of late RNs.…”

Chromosome pairing and chiasma formation in spermatocytes and oocytes of Dendrocoelum lactem (Turbellaria, Tricladida); a cytogenetical and ultrastructural study

“…Marked SC shortening between (Carpenter, 1979b(Carpenter, , 1984Rasmussen and Holm, 1978). From the rather limited number of species which have been examined, it appears that the RNs of closely related species are more similar in size and shape than those of more distantly related species (Carpenter, 1979b). The RNs of D. lacteum are small spherical structures, not exceeding 70 nm in diameter.…”

Electron microscopical analysis of meiotic chromosomes from human spermatocytes during and after treatment with steroid hormones

“…From the first appearance of synaptonemal complexes at the beginning of zygotene electron dense nodules can be recognized in or at the central region of the synaptonemal complex. These so-called recombination nodules measure 30-150 nm, are usually spherical or rod-shaped ( Figures 3 and 4) and considered to participate in crossing over (2,3). At mid and late pachytene the number of recombination nodules is reduced to 5-10 per nucleus.…”