SPATIAL ORGANIZATION OF CHROMOSOMES IN MALARIA MOSQUITOES.

Malaria mosquitoes are vectors of dangerous human diseases and a model system for investigations of chromosome evolution, heterochromatin organization, and nuclei architecture in the cells of the reproductive system. Investigations of nurse cells chromosomes are aimed at understanding of mechanisms that cause interspecies differences in the nuclear spatial organization in these cells. One of the most important tasks of this research is the undestanding of molecular organization of the chromosome regions that are attached to the nuclear envelope. In the present review, the recent achievements in this field of research are described and unsolved problems of the spatial chromosome organization are identified.

[Spatial and temporal variations of the chromosomal inversion frequencies across the range of malaria mosquito Anopheles messeae Fall. (Culicidae) during the 40-year monitoring period].

The analysis of personal and published data on the frequency dynamics of chromosomal inversions within the range of Anopheles messeae obtained during the period from 1974 through 2014 is presented. The results showed that, in general, across the species range, during the 40 years of genetic monitoring, there was a steady (stationary) clinal distribution of inversions in the first decade (1974­1985). Then, over the period of five years (1986­1990), there was a considerable change in the inversion frequencies in favor of southwestern chromosomal variants (particularly strongly fixed in the Tomsk population), and from 1992 to the present time, these changes remained and were relatively stably reproduced in most parts of the range. It was noted that the jump in warming during the winter of 1981­1982 led to a correlated jump of the southwestern chromosomes in the Tomsk population. In connection with the general tendency toward the increase in average winter temperatures, a sharp decrease in the 2R1 chromosome frequency in the Siberian region and Syktyvkar in the period from 1992 to the present time was observed. There is reason to assume that, over the past decade, the northern boundary of the An. messeae range moved northward to the tundra zone.

[Comparative Analysis of DNA Sequences of Regions of X-Chromosome Attachment to the Nuclear Envelope of Nurse Cells Anopheles messeae Fall].

Polytene chromosomes of ovarian nurse cells of Anopheles mosquitoes form strong contacts with the nuclear envelope. The presence of contacts, their position at nurse cell chromosomes, and their morphological features are species-specific in malaria mosquitoes. It is important to determine the nature of these interspecies differences in the nuclear architecture, both to understand the function of the nucleus and to assess the role of the spatial organization of chromosomes in evolution. Using dot-blot hybridization, we compared DNA sequences of the clone library from the X-chromosome attachment region to the nuclear envelope of ovarian nurse cells of Anopheles messeae with DNA-probes: (1) of the X-chromosome attachment region of An. atroparvus, (2) of the 3R chromosome attachment region ofAn. messeae, and (3) of the chromosome 2 pericentromeric region of An. messeae, without expressed contacts with the nuclear envelope. It has been shown that the chromosome attachment regions have a significantly higher number of homologous DNA sequences as compared with the pericentromeric region of chromosome 2. Sequences that are common for attachment regions are largely potentially able to participate in the formation of chromatin loop domains and to interact with some nucleus frameworks, according to the analysis in the ChrClass program. The obtained results support the important role of DNA in the formation of strong chromosomal attachments to the nuclear envelope in nurse cells of Anopheles mosquitoes.

A standard photomap of ovarian nurse cell chromosomes in the European malaria vector Anopheles atroparvus.

Anopheles atroparvus (Diptera: Culicidae) is one of the main malaria vectors of the Maculipennis group in Europe. Cytogenetic analysis based on salivary gland chromosomes has been used in taxonomic and population genetic studies of mosquitoes from this group. However, a high-resolution cytogenetic map that could be used in physical genome mapping in An. atroparvus is still lacking. In the present study, a high-quality photomap of the polytene chromosomes from ovarian nurse cells of An. atroparvus was developed. Using fluorescent in situ hybridization, 10 genes from the five largest genomic supercontigs on the polytene chromosome were localized and 28% of the genome was anchored to the cytogenetic map. The study established chromosome arm homology between An. atroparvus and the major African malaria vector Anopheles gambiae, suggesting a whole-arm translocation between autosomes of these two species. The standard photomap constructed for ovarian nurse cell chromosomes of An. atroparvus will be useful for routine physical mapping. This map will assist in the development of a fine-scale chromosome-based genome assembly for this species and will also facilitate comparative and evolutionary genomics studies in the genus Anopheles.