Evolutionary regularities of development of somatic polyploidy in salivary glands of gastropod mollusks: V. Subclasses Opisthobranchia and Pulmonata

Abstract

Abstract⎯Salivary glands of 25 species of Opisthobranchia and Pulmonata gastropod mollusks were studied with the use of histochemical methods and cytophotometry of DNA in cellular nuclei. In the secretory epi thelium, cells of three main types are identified: granular cells (with granular glycoprotein inclusions), muco cytes I (containing sulphatized acid mucopolysaccharides), and mucocytes II (containing neutral and acid nonsulphatized polysaccharides and protein), as well as epithelial ciliated cells and cells of ducts. It is shown that the salivary gland secretory cells of all studied mollusk species are polyploidized, but to different degree. In most species, the maximal degree of polyploidy estimated by the DNA content amounts to 64-128c. Giant polyploidy-up to 4096c-is revealed in salivary gland cells of Tritonia diomedea. The functional properties due to the peculiarities of nutrition of different molluscan species and phylogenetic tendencies of develop ment of somatic polyploidy in the class of Gastropoda are discussed. The high degree of obligatory polyp loidization revealed in salivary gland cells of the opisthobranchian and pulmonate mollusks is considered as a peculiar cytological arogenesis as compared with allogenic, facultative, and slight manifestations of polyp loidy in prosobranchian gastropod mollusks. The probable causes of such differences are due to the euthy neural type of organization of the central nervous system and to the giant neuronal polyploidy in opisthobran chian and pulmonate mollusks. The causes, mechanisms, and significance of such correlations are so far unclear.

Chromosomal Evolution in Mole Voles Ellobius (Cricetidae, Rodentia): Bizarre Sex Chromosomes, Variable Autosomes and Meiosis

“…It is known that formation of sporadic polyploid cells is possible in humans and animals [ 72 ]. Although somatic polyploidy is widely known among animals and humans [ 73 , 74 ], polyploid germ cells are rarely detected. Tetraploid pachytene spermatocytes were detected in mice using EM by Solari and Moses [ 75 ] and in humans using immunocytochemical analysis by Codino-Pascual and colleagues [ 76 ].…”

Endopolyploidy as a potential driver of animal ecology and evolution

“…Such tests would range from addressing whether there are phylogenetic patterns in the incidence of endopolyploidy (e.g. Anisimov & Zyumchenko, ) and whether there exist specific ecological ‘syndromes’ (i.e. terrestrial, marine, freshwater) that might favour the evolution of endopolyploidy, to determining whether endopolyploidy is more prevalent in secretory tissues (e.g.…”

“…Despite the remarkable diversity of taxa and tissues that feature endopolyploidy, the cellular mechanisms that lead to endopolyploidy are broadly similar, featuring either alternating S phases and G phases in the absence of mitosis or an abbreviated mitosis without completion of cytokinesis (Lee et al ., ; Edgar et al ., ). At face value, these patterns might suggest that the specific mechanisms underlying endopolyploidy are ancient and highly conserved, although the phylogenetic distribution of the various distinct molecular mechanisms leading to endopolyploidy suggests that endopolyploidy has evolved independently on multiple occasions in different taxa and different tissue types through evolutionary time (Anisimov, ; Anisimov & Zyumchenko, ; Edgar et al ., ).…”

Morphology of the buccal apparatus of Dendronotus frondosus (Gastropoda: Nudibranchia)

“…The somatic polyploidy is believed to be adaptive to the euthyneuran anatomy. It also may have a phylogenetic significance, as, among Gastropoda, it is reported only for Euthyneura (Anisimov & Zyumchenko, 2012). Assumedly, the polyploid euthyneuran odontoblasts are another case of the somatic polyploidy.…”

“…Since the cell size often correlates with the ploidy (Rudra & Warner, 2004), one may assume that the euthyneuran odontoblasts are polyploid. Polyploidy in neurons and in protein-synthetic and mucous cells in the salivary glands of euthyneuran molluscs was previously reported (Anisimov & Zyumchenko, 2012;Boer et al, 1976;Schreiber & Schreiber, 1964;Swift, 1953). This phenomenon was called 'somatic polyploidy'.…”