Ontogenez

Genes of the ANTP class are known as evolutionary conserved and hierarchically high-level regulators of development. They are the most studied and the most numerous homeobox genes in animals. These genes encode homeodomain transcription factors and possess a set of unique features, such as clustering, colinearity, evolutionary conservation, and consistent involvement in various differentiation processes throughout the ontogeny of multicellular animals.

The first ANTP genes (from the NK subclass) appear in ctenophores and sponges, which is why the evolution of Metazoa from a common unicellular ancestor is often associated with the emergence of the ANTP class (Larroux et al., 2007; Moroz et al., 2014). Phylogenetic analysis of homeobox genes, conducted across a broad range of basal Metazoa taxa, has shown that ANTP genes from the Hox and ParaHox subclasses arose in the last common ancestor of Cnidaria and Bilateria. These new findings raise further questions. How does the evolution of these clusters correlate with the evolution of animals? What functions were acquired by the new genes, and which were inherited from ancestral NK genes? What changes in their regulation could have influenced the evolution of body plans in Metazoa? Is it even possible to answer these questions by studying modern multicellular organisms?

This review aims to address these and other questions regarding the evolution of ANTP gene clusters. Special attention is given to the concept of the “megacluster” — a hypothetical synteny that united all ANTP subclasses at the dawn of Metazoa evolution.

The decreasing cost of sequencing technologies offers some hope for answers, as it expands the range of model species available for study. The broader this range, the easier it becomes to identify universal and lineage-specific patterns of molecular and morphological evolution.

In this article, I analyze the outstanding contribution of Russian-American researcher Vera Danchakoff (1879–1950) — her pioneering work on the blood stem cells and on the plasticity of embryonic development. I argue that, working along the same lines, as the Russian histologist Alexander Maximow, Danchakoff described the unique properties of the “polyvalent” (pluripotent) stem cells, and was, in fact, the first author who used the term “stem cell” in its modern meaning in her 1917 publication. Developing the idea of polyvalent cell differentiation, she applied it to embryonic development in her research on the cultivation of human embryonic tissues on the chorioallantoic membrane of chicken. I show that these experiments, which Danchakoff conducted during her stay in Soviet Russia in 1926–1932, were formative for her later research on the problem of sex determination and the bipotentiality of primordia of the gonads and sexual organs.

A characteristic feature of Caucasian rock lizards is the diversity of parthenogenetic species and the ongoing processes of interspecific hybridization in the zones of sympatry of unisexual and bisexual species with the formation of polyploid hybrids. This is the reason for the interest in studying the species composition of various, especially mixed, populations of Darevskia. According to the preliminary description of the morphological characteristics of lizards from the previously unstudied Jradzor population of Armenia, it was assumed that only unisexual individuals live in it, but the affiliation of the species was questioned. In the present work, microsatellite genotyping of lizards from this population (n = 24) was carried out using locus-specific PCR and subsequent full-length sequencing of the identified alleles. As a result, the species composition of this sample was established, including individuals of the parthenospecies Darevskia dahli, D. unisexualis, and D. armeniaca. Individuals identified as D. dahli have the same alleles from the studied loci as in other populations of Armenia. However, the multilocus genotypes formed by the alleles are different. The individual identified as D. armeniaca carries the most common multilocus genotype. In D. unisexualis individuals, a new allele (allele B) was identified at the Du281 locus, which reflects the phenomenon of intraspecific polymorphism of parthenogenetic species. Thus, an unusual feature of the Jradzor population is the sympatric habitation of three and possibly four parthenogenetic species of Darevskia, if the presence of D. uzzellii in Armenia is further confirmed.