Somatic pairing, endomitosis and chromosome aberrations in snakes (Viperidae and Colubridae)

Abstract

The positioning of macrochromosomes of Bothrops jararaca and Bothrops insularis (Viperidae) was studied in undistorted radial metaphases of uncultured cells (spermatogonia and oogonia) not subjected to spindle inhibitors. Colchicinized metaphases from uncultured (spleen and intestine) and cultured tissues (blood) were also analyzed. We report two antagonic non-random chromosome arrangements in untreated premeiotic cells: the parallel configuration with homologue chromosomes associated side by side in the metaphase plate and the antiparallel configuration having homologue chromosomes with antipolar distribution in the metaphase ring. The antiparallel aspect also appeared in colchicinized cells. The spatial chromosome arrangement in both configurations is groupal size-dependent and maintained through meiosis. We also describe, in untreated gonia cells, endomitosis followed by reductional mitosis which restores the diploid number. In B. jararaca males we observed that some gonad regions present changes in the meiotic mechanism. In this case, endoreduplicated cells segregate the diplochromosomes to opposite poles forming directly endoreduplicated second metaphases of meiosis with the suppression of first meiosis. By a successive division, these cells form nuclei with one set of chromosomes. Chromosome doubling in oogonia is known in hybrid species and in parthenogenetic salamanders and lizards. This species also presented chromosome rearrangements leading to aneuploidies in mitosis and meiosis. It is suggested that somatic pairing, endomitosis, meiotic alterations, and chromosomal aberrations can be correlated processes. Similar aspects of nuclei configurations, endomitosis and reductional mitosis were found in other Viperidae and Colubridae species.

First Cytogenetic Study of Puff-Faced Water Snake, <i>Homalopsis buccata</i> (Squamata, Colubridae) by Conventional Staining, Ag-NOR Banding and GTG-Banding Techniques

“…Interstitial C-bands were seldom reported (Oguiura et al 2010). While, Beçak et al (2003) reported that among Colubridae species there is wild variation of chromosome number and different levels of sex chromosome differentiation. A common feature in Reptilia is the presence of macrochromosomes and microchromosomes, probably due to karyological ancestral derivation from forms that already presented this attribute.…”

“…Moreover, even microchromosomes that are apparently totally heterochromatic may have some euchromatin in them. This condition may be or not advantageous, depending on environmental conditions (Olmo 2005, 2008, Beçak et al 2003. Hydrodynastes bicinctus bicinctus has 2n=24, a very small diploid chromosome number for snakes and no microchromosomes (Beçak and Beçak 1969), which may be interpreted as a formation of favorable linkage groups.…”

“…From a literature review about cytogenetic studies of snakes in the family Colubridae, covering reports by Nakamura (1927Nakamura ( , 1928Nakamura ( , 1935, Matthey (1931), Bhatnager (1959, Beçak (1965), Kobel (1967), Fischman et al (1968), Beçak and Beçak (1969), Bury et al (1970), Dutt (1970), Gorman and Gress (1970), Singh et al (1970), Baker et al (1972), Singh (1972), Gutiérrez et al (1984), Moreno et al (1987), Ota and Iwanaga (1996), Ota (1999), Beçak et al (2003) and Aprea et al (2003). The present cytogenetic study, the report on karyotype analysis and chromosomal characteristic of the nucleolar organizer regions (NORs) of H. uccata, is the first record.…”

Genetic stability of senescence reverted cells: Genome reduction division of polyploidy cells, aneuploidy and neoplasia

“…They could be due to a reawakening process of normal G 0 /G 1 diploid, flat cells and/or to a special type of mitotic division of endopolyploid cells. [13][14][15][16] Polyploidy associated with senescence is generally assessed by flow cytometry which gives no information as to mode of mitotic cycling. 2,[17][18][19] The special type of endopolyploidy had shown production of genome reduced cells (e.g., 4n/8C to 2n/2C) with chromosomal abnormalities occurring immediately before (i.e., pre-senescence) the change to flat cells-only.…”

Neoplastic-Like CELL Changes of Normal Fibroblast Cells Associated with Evolutionary Conserved Maternal and Paternal Genomic Autonomous Behavior (Gonomery)

“…The earlier literature associated the tetraploid-condition with formation of 46, 4-chromatid diplochromosomes (4n/8C) i.e., from endo-reduplication [10] [28]. Presently there is increasing mentioning of endoreplication, but its chromosomal structural consequence (4-chromatid chromosomes) as distinct from regular, genomic doubling to 92 chromosomes lacks understanding regarding a non-mitotic division [29]- [32]. Even when encountered in cancer-cytogenetics, there appears to be no curiosity about their division-behavior, which was a major interest for mouse ascites tumor cells some decades ago [33].…”