On the Structural Organization of the Transcriptional Unit in Animal Chromosomes

Three levels of genome organization in eukaryotes are considered in this paper: (1) the structure of the transcriptional unit (or transcripton); (2) the arrangement of proteins along unfolded chromosomal DNA in chromatin; and (3) the mode of DNA packing in the chromatin

Molecular genetic characteristics of Darevskia portschinskii lizard populations based on microsatellite markers analysis

The Caucasian rock lizard species Darevskia portschinskii is one of the bisexual species participating in interspecific hybridisation as the paternal ancestor with the maternal ancestors D. mixta and D. raddei resulting in the successful formation of the parthenogenetic D. dahli and D. rostombekowi, respectively. Populations of D. portschinskii have been previously divided into two subspecies, D. p. portschinskii and D. p. nigrita according to their geographical distribution and the morphological data, but they have not been characterised genetically. Here, we used ten microsatellite markers to determine the genetic structure of the D. portschinskii populations. The utility of the developed microsatellite markers for investigating the genetic variability within and among populations with a heterogeneous spatial distribution was demonstrated. Our results showed that the intra- and interspecific differentiation of the studied populations were consistent with the morphological data on the subspecies status of the D. p. portschinskii and D. p. nigrita populations. A potential applicability of the developed microsatellite markers to study genetic diversity of Darevskia species and subspecies complexes is suggested

Genetic Variation and De Novo Mutations in the Parthenogenetic Caucasian Rock Lizard Darevskia unisexualis

Unisexual all-female lizards of the genus Darevskia that are well adapted to various habitats are known to reproduce normally by true parthenogenesis. Although they consist of unisexual lineages and lack effective genetic recombination, they are characterized by some level of genetic polymorphism. To reveal the mutational contribution to overall genetic variability, the most straightforward and conclusive way is the direct detection of mutation events in pedigree genotyping. Earlier we selected from genomic library of D. unisexualis two polymorphic microsatellite containg loci Du281 and Du215. In this study, these two loci were analyzed to detect possible de novo mutations in 168 parthenogenetic offspring of 49 D. unisexualis mothers and in 147 offspring of 50 D. armeniaca mothers . No mutant alleles were detected in D. armeniaca offspring at both loci, and in D. unisexualis offspring at the Du215 locus. There were a total of seven mutational events in the germ lines of four of the 49 D. unisexualis mothers at the Du281 locus, yielding the mutation rate of 0.1428 events per germ line tissue. Sequencing of the mutant alleles has shown that most mutations occur via deletion or insertion of single microsatellite repeat being identical in all offspring of the family. This indicates that such mutations emerge at the early stages of embryogenesis. In this study we characterized single highly unstable (GATA)n containing locus in parthenogenetic lizard species D. unisexualis. Besides, we characterized various types of mutant alleles of this locus found in the D. unisexualis offspring of the first generation. Our data has shown that microsatellite mutations at highly unstable loci can make a significant contribution to population variability of parthenogenetic lizards

Functional Expression Cloning of Nanog, a Pluripotency Sustaining Factor in Embryonic Stem Cells.

Embryonic stem (ES) cells undergo extended proliferation while remaining poised for multilineage differentiation. A unique network of transcription factors may characterize self-renewal and simultaneously suppress differentiation. We applied expression cloning in mouse ES cells to isolate a self-renewal determinant. Nanog is a divergent homeodomain protein that directs propagation of undifferentiated ES cells. Nanog mRNA is present in pluripotent mouse and human cell lines, and absent from differentiated cells. In preimplantation embryos, Nanog is restricted to founder cells from which ES cells can be derived. Endogenous Nanog acts in parallel with cytokine stimulation of Stat3 to drive ES cell self-renewal. Elevated Nanog expression from transgene constructs is sufficient for clonal expansion of ES cells, bypassing Stat3 and maintaining Oct4 levels. Cytokine dependence, multilineage differentiation, and embryo colonization capacity are fully restored upon transgene excision. These findings establish a central role for Nanog in the transcription factor hierarchy that defines ES cell identity