Centromere repositioning explains fundamental number variability in the New World monkey genus <Emphasis Type="Italic">Saimiri</Emphasis>

Cytogenetics has historically played a key role in research on squirrel monkey (genus Saimiri) evolutionary biology. Squirrel monkeys have a diploid number of 2n = 44, but vary in fundamental number (FN). Apparently, differences in FN have phylogenetic implications and are correlated with geographic regions. A number of hypothetical mechanisms were proposed to explain difference in FN: translocations, heterochromatin, or, most commonly, pericentric inversions. Recently, an additional mechanism, centromere repositioning, was discovered, which can alter chromosome morphology and FN. Here, we used chromosome banding, chromosome painting, and BAC-FISH to test these hypotheses. We demonstrate that centromere repositioning on chromosomes 5 and 15 is the mechanism that accounts for differences in FN. Current phylogenomic trees of platyrrhines provide a temporal framework for evolutionary new centromeres (ENC) in Saimiri. The X-chromosome ENC could be up to 15 million years (my) old that on chromosome 5 as recent as 0.3 my. The chromosome 15 ENC is intermediate, as young as 2.24 my. All ENC have abundant satellite DNAs indicating that the maturation process was fairly rapid. Callithrix jacchus was used as an outgroup for the BAC-FISH data analysis. Comparison with scaffolds from the S. boliviensis genome revealed an error in the last marmoset genome release. Future research including at the sequence level will provide better understanding of chromosome evolution in Saimiri and other platyrrhines. Probably other cases of differences in chromosome morphology and FN, both within and between taxa, will be shown to be due to centromere repositioning and not pericentric inversions.     

Effects of α-latrotoxin on synaptic transmission between identified neurons in the snail central nervous system

The effects of -latrotoxin — a component of black widow spider venom — on an identified monosynaptic peptidergic synapse were investigated in the central nervous system ofHelix pomatia. Extracellular and intracellular application of the toxin was found to increase and block postsynaptic current respectively. Current induced by intracellular injection of cAMP which imitates postsynaptic current was inhibited, irrespective of the mode of toxin application. It was concluded on the basis of the experiments performed that -latrotoxin manifests its reinforcing effect, acting on the transmitter release system in the presynaptic neuron. It can also induce an inhibitory effect, however, operating on the postsynaptic cell direct — an effect which may be mediated by the cAMP system.A. A. Bogomolets Institute of Physiology, Ukrainian Academy of Sciences, Kiev. A. A. Bogomolets Medical Institute of Biochemistry, Ukrainian Academy of Sciences, Kiev. Translated from Neirofiziologiya, Vol. 24, No. 4, pp. 430–437, July–August, 1992.     

Low-pass single-chromosome sequencing of human small supernumerary marker chromosomes (sSMCs) and <Emphasis Type="Italic">Apodemus</Emphasis> B chromosomes

Supernumerary chromosomes sporadically arise in many eukaryotic species as a result of genomic rearrangements. If present in a substantial part of species population, those are called B chromosomes, or Bs. This is the case for 70 mammalian species, most of which are rodents. In humans, the most common types of extra chromosomes, sSMCs (small supernumerary marker chromosomes), are diagnosed in approximately 1 of 2000 postnatal cases. Due to low frequency in population, human sSMCs are not considered B chromosomes. Genetic content of both B-chromosomes and sSMCs in most cases remains understudied. Here, we apply microdissection of single chromosomes with subsequent low-pass sequencing on Ion Torrent PGM and Illumina MiSeq to identify unique and repetitive DNA sequences present in a single human sSMC and several B chromosomes in mice Apodemus flavicollis and Apodemus peninsulae. The pipeline for sequencing data analysis was made available in Galaxy interface as an addition to previously published command-line version. Human sSMC was attributed to the proximal part of chromosome 15 long arm, and breakpoints leading to its formation were located into satellite DNA arrays. Genetic content of Apodemus B chromosomes was species-specific, and minor alterations were observed in both species. Common features of Bs in these Apodemus species were satellite DNA and ERV enrichment, as well as the presence of the vaccinia-related kinase gene Vrk1. Understanding of the non-essential genome elements content provides important insights into genome evolution in general.     

The polysaccharide glycocalyx of Pseudomonas syringae pv. atrofaciens

It was shown by the method of electron microscopy that cells of virulent strain Pseudomonas syringae rv. atrofaciens 4394 have extracellular, probably, polysaccharide glycocalix. It consists of acid components giving positive cytochemical reaction with ruthenium red, a specific reagent to polyanions.     

Effect of sphingomyelin and its enzymatic hydrolysis products on heterologous methylation of calf thymus DNA by cytosine-DNA-methyltransferase EcoRII

It was found that sphingomyelin and its enzymatic hydrolysis products, choline and sphingosine, influence the degree of DNA methylation in the reaction of heterologous methylation by methylase EcoRII in vitro. Sphingomyelin was found to be able to was activate (by 20%), sphingosine and choline inhibit methylation. Phosphatidylcholine had no effect on DNA methylation in an in vitro system. The role of lipids in the regulation of gene expression during enzymatic modification (methylation) of DNA is discussed.