Comparative cytogenetic study on two species of the genus Entedon Dalman, 1820 (Hymenoptera, Eulophidae) using DNA-binding fluorochromes and molecular and immunofluorescent markers

Structure and Evolution of Ribosomal Genes of Insect Chromosomes

Currently, clusters of 45S and 5S ribosomal DNA (rDNA) have been studied in about 1000 and 100 species of the class Insecta, respectively. Although the number of insect species with known 45S rDNA clusters (also referred to as nucleolus-organizing regions, or NORs) constitutes less than 0.1 percent of the described members of this enormous group, certain conclusions can already be drawn. Since haploid karyotypes with single 45S and 5S rDNA clusters predominate in both basal and derived insect groups, this character state is apparently ancestral for the class Insecta in general. Nevertheless, the number, chromosomal location, and other characteristics of both 45S and 5S rDNA sites substantially vary across different species, and sometimes even within the same species. There are several main factors and molecular mechanisms that either maintain these parameters or alter them on the short-term and/or long-term scale. Chromosome structure (i.e., monocentric vs. holokinetic chromosomes), excessive numbers of rRNA gene copies per cluster, interactions with transposable elements, pseudogenization, and meiotic recombination are perhaps the most important among them.

Chromosome study of the Hymenoptera (Insecta): from cytogenetics to cytogenomics

A brief overview of the current stage of the chromosome study of the insect order Hymenoptera is given. It is demonstrated that, in addition to routine staining and other traditional techniques of chromosome research, karyotypes of an increasing number of hymenopterans are being studied using molecular methods, e.g., staining with base-specific fluorochromes and fluorescence in situ hybridization (FISH), including microdissection and chromosome painting. Due to the advent of whole genome sequencing and other molecular techniques, together with the "big data" approach to the chromosomal data, the current stage of the chromosome research on Hymenoptera represents a transition from Hymenoptera cytogenetics to cytogenomics.

Comparative Karyotype Analysis of Parasitoid Hymenoptera (Insecta): Major Approaches, Techniques, and Results

A comprehensive review of main approaches, techniques and results of the chromosome study of parasitic wasps is given. In this group, the haploid chromosome number ranges from n = 3 to 23. Distribution of parasitic wasp species by the chromosome number is bimodal, with two obvious modes at n = 6 and 11. Karyotype analysis based on routinely stained preparations of mitotic chromosomes can be used to identify members of taxonomically complicated parasitoid taxa and to distinguish between them. Morphometric study effectively reveals subtle differences between similar chromosome sets of parasitic wasps. If combined with meiotic analysis and/or cytometric data, information on mitotic karyotypes can highlight pathways of the genome evolution in certain parasitoid taxa. C- and AgNOR-banding as well as staining with base-specific fluorochromes detected important interspecific differences within several groups of parasitic wasps. Fluorescence in situ hybridization (FISH) is successfully used for physical mapping of various DNA sequences on parasitoid chromosomes. These techniques demonstrate that heterochromatic segments are usually restricted to pericentromeric regions of chromosomes of parasitic wasps. Haploid karyotypes carrying one or two nucleolus organizing regions (NORs) are the most frequent among parasitoid Hymenoptera. In combination with chromosome microdissection, FISH could become a powerful tool exploring the genome evolution of parasitic wasps. Perspectives of the comparative cytogenetic study of parasitoid Hymenoptera are outlined.

Chromosomes of parasitic wasps of the superfamily Chalcidoidea (Hymenoptera): An overview

An overview of the current knowledge of chromosome sets of the parasitoid superfamily Chalcidoidea is given. Karyotypes of approximately 240 members of this group, i.e. just above one percent of described species, are studied up to now. Techniques for obtaining and analyzing preparations of chalcid chromosomes are outlined, including the so-called "traditional" and "modern" methods of differential staining as well as fluorescence in situ hybridization (FISH). Among the Chalcidoidea, the haploid chromosome number can vary from n = 3 to n = 11, with a clear mode at n = 6 and a second local maximum at n = 10. In this group, most chromosomes are either metacentric or submetacentric, but acrocentrics and/or subtelocentrics also can predominate, especially within karyotypes of certain Chalcidoidea with higher chromosome numbers. The following main types of chromosomal mutations are characteristic of chalcid karyotypes: inversions, fusions, translocations, polyploidy, aneuploidy and B chromosome variation. Although karyotype evolution of this superfamily was mainly studied using phylogenetic reconstructions based on morphological and/or molecular characters, chromosomal synapomorphies of certain groups were also revealed. Taxonomic implications of karyotypic features of the Chalcidoidea are apparently the most important at the species level, especially among cryptic taxa.

Inter-Cell and Inter-Chromosome Variability of 5-Hydroxymethylcytosine Patterns in Noncultured Human Embryonic and Extraembryonic Cells

5-hydroxymethylcytosine (5hmC) is an oxidative derivative of 5-methylcytosine (5mC). Recent studies have revealed a sharp difference in the levels of 5hmC in 2 opposite DNA strands of a given chromosome and a chromosome-wide cell-to-cell variability in mammalian cells. This asymmetric 5hmC distribution was found in cultured cells, which may not fully mimic in vivo epigenetic processes. We have checked whether inter-chromosome and inter-cell variability of 5hmC patterns is typical for noncultured human cells. Using indirect immunofluorescence, we analyzed the localization of 5hmC and its co-distribution with 5mC on direct preparations of mitotically active cells from human embryonic lung and chorionic cytotrophoblast samples. We demonstrated 3 types of chromosomes according to the 5hmC accumulation pattern: hydroxymethylated (5hmC in both sister chromatids), hemihydroxymethylated (5hmC in only 1 sister chromatid), and nonhydroxymethylated ones. Each accumulation type was not specific to any particular chromosome, resulting in different 5hmC patterns between homologous chromosomes, among chromosomes within each metaphase plate, among metaphases in one tissue, and between the tissues. The 5mC distribution was stable: chromosomes were methylated in R-bands and, especially in embryonic lung cells, in the heterochromatic regions 1q12, 9q12, and 16q11.2. Our results provide the first evidence of inter-cell and inter-chromosome variability of 5hmC patterns in human noncultured embryonic and extraembryonic cells.

A cytogenetic study of three parasitic wasp species (Hymenoptera, Chalcidoidea, Eulophidae, Trichogrammatidae) from Brazil using chromosome morphometrics and base-specific fluorochrome staining

Chromosomes of three chalcid wasp species from Brazil, Palmistichus elaeisis Delvare et LaSalle, 1993, Trichospilus diatraeae Cherian et Margabandhu, 1942 (both belonging to the family Eulophidae) and Trichogramma pretiosum Riley, 1879 (Trichogrammatidae), were studied using chromosome morphometrics and base-specific fluorochrome staining. The present study confirmed that these species respectively have 2n = 12, 14 and 10. Chromomycin A3 / 4', 6-diamidino-2-phenylindole (CMA3/DAPI) staining revealed a single CMA3-positive and DAPI-negative band within haploid karyotypes of both Palmistichus elaeisis and Trichogramma pretiosum. This CG-rich band clearly corresponds to the nucleolus organizing region (NOR). Moreover, analogous multiple telomeric bands found on all chromosomes of Trichospilus diatraeae may also represent NORs. Certain features of karyotype evolution of the phylogenetic lineage comprising both Eulophidae and Trichogrammatidae are discussed. The results obtained during the present study demonstrate the importance of chromosome research on tropical parasitoids that remain poorly known in this respect.

A comparative cytogenetic study of Drosophila parasitoids (Hymenoptera, Figitidae) using DNA-binding fluorochromes and FISH with 45S rDNA probe

Karyotypes of Leptopilina boulardi (Barbotin, Carton et Keiner-Pillault, 1979) (n = 9), L. heterotoma (Thomson, 1862) (n = 10), L. victoriae Nordlander, 1980 (n = 10) and Ganaspis xanthopoda (Ashmead, 1896) (n = 9) (Hymenoptera, Figitidae) were studied using DNA-binding ligands with different base specificity [propidium iodide (PI), chromomycin A3 (CMA3) and 4',6-diamidino-2-phenylindole (DAPI)], and fluorescence in situ hybridization (FISH) with a 45S rDNA probe. Fluorochrome staining was similar between the different fluorochromes, except for a single CMA3- and PI-positive and DAPI-negative band per haploid karyotype of each species. FISH with 45S rDNA probe detected a single rDNA site in place of the bright CMA3-positive band, thus identifying the nucleolus organizing region (NOR). Chromosomal locations of NORs were similar for both L. heterotoma and L. victoriae, but strongly differed in L. boulardi as well as in G. xanthopoda. Phylogenetic aspects of NOR localization in all studied species are briefly discussed.

Karyotypes of parasitic wasps of the family Eulophidae (Hymenoptera) attacking leaf-mining Lepidoptera (Gracillariidae, Gelechiidae)

Karyotypes of eleven parasitoid species of the family Eulophidae were examined, namely, Chrysocharis laomedon (Walker, 1839) (2n = 10), Chrysocharis sp. aff. laomedon (n = 5, 2n = 10), Chrysocharis sp. aff. albipes (Ashmead, 1904) (2n = 12), Mischotetrastichus petiolatus (Erdös, 1961) (n = 6, 2n = 12), Minotetrastichus frontalis (Nees, 1834) (n = 5, 2n = 10), Cirrospilus pictus (Nees, 1834) (2n = 12), Hyssopus geniculatus (Hartig, 1838) (2n = 16), Sympiesis gordius (Walker, 1839) (2n = 12), S. sericeicornis (Nees, 1834) (2n = 12), Pnigalio agraules (Walker, 1839) (2n = 12 + 0-2B) and Pnigalio gyamiensis Myartseva & Kurashev, 1990 (2n = 12 + 0-6B) reared from Phyllonorycter acerifoliella (Zeller, 1839), Ph. apparella (Herrich-Schäffer, 1855), Ph. issikii (Kumata, 1963) (Gracillariidae) and Chrysoesthia sexguttella (Thunberg, 1794) (Gelechiidae). Chromosome sets of all species except P. agraules and P. gyamiensis were studied for the first time. B chromosomes were detected in the two latter species; in P. gyamiensis, the maximum number of B chromosomes represents the highest value known for parasitic wasps to date.