Chromosome Mapping of H1 and H4 Histones in Parodontidae (Actinopterygii: Characiformes): Dispersed and/or Co-Opted Transposable Elements?

The karyotypes of the family Parodontidae consist of 2n = 54 chromosomes. The main chromosomal evolutionary changes of its species are attributed to chromosome rearrangements in repetitive DNA regions in their genomes. Physical mapping of the H1 and H4 histones was performed in 7 Parodontidae species to analyze the chromosome rearrangements involved in karyotype diversification in the group. In parallel, the observation of a partial sequence of an endogenous retrovirus (ERV) retrotransposon in the H1 histone sequence was evaluated to verify molecular co-option of the transposable elements (TEs) and to assess paralogous sequence dispersion in the karyotypes. Six of the studied species had an interstitial histone gene cluster in the short arm of the autosomal pair 13. Besides this interstitial cluster, in Apareiodon davisi, a probable further site was detected in the terminal region of the long arm in the same chromosome pair. The H1/H4 clusters in Parodon cf. pongoensis were located in the smallest chromosomes (pair 20). In addition, scattered H1 signals were observed on the chromosomes in all species. The H1 sequence showed an ERV in the open reading frame (ORF), and the scattered H1 signals on the chromosomes were attributed to the ERV's location. The H4 sequence had no similarity to the TEs and displayed no dispersed signals. Furthermore, the degeneration of the inner ERV in the H1 sequence (which overlapped a stretch of the H1 ORF) was discussed regarding the likelihood of molecular co-option of this retroelement in histone gene function in Parodontidae.

Preexisting heterogeneities in gene dosage sensitivity shaped sex chromosome evolution in mammals and birds

Mammalian X and Y chromosomes evolved from an ordinary autosomal pair; genetic decay decimated the Y, which in turn necessitated X chromosome inactivation (XCI). Genes of the ancestral autosomes are often assumed to have undertaken these transitions on uniform terms, but we hypothesized that they varied in their dosage constraints. We inferred such constraints from conservation of microRNA (miRNA)-mediated repression, validated by analysis of experimental data. X-linked genes with a surviving Y homolog have the most conserved miRNA target sites, followed by genes with no Y homolog and subject to XCI, and then genes with no Y homolog but escaping XCI; this heterogeneity existed on the ancestral autosomes. Similar results for avian Z-linked genes, with or without a W homolog, lead to a model of XY/ZW evolution incorporating preexisting dosage sensitivities of individual genes in determining their evolutionary fates, and ultimately shaping the mammalian and avian sex chromosomes.

Possible origin of B chromosome in Dichotomius sericeus (Coleoptera)

B chromosomes have so far been described in about 80 species of Coleoptera, mainly using conventional staining analysis. In this study, 152 individuals of the dung beetle Dichotomius sericeus (Coleoptera), collected from three isolated geographical areas in the State of Pernambuco, Brazil, were analyzed to determine the frequency, prevalence, distribution, meiotic behavior, and possible B chromosome origin. The cytogenetic analysis consisted of conventional staining, C-banding, triple fluorochrome staining (CMA3/DA/DAPI), and fluorescent in situ hybridization using ribosomal DNAs (rDNAs) and H3 histone gene as probes, as well as microdissection and chromosome painting of the B chromosome. The B chromosomes were detected in all populations analyzed. Analysis revealed the heterochromatic nature and the presence of G+C-rich blocks and 18S rDNA on the B chromosome. FISH with DNA from microdissected B chromosome painted the entire extension of the B chromosome for all populations, besides the pericentromeric regions of all the autosomes, as well as the X chromosome. Finally, cross-hybridization in nine related species of Dichotomius using the microdissected B chromosome as probe did not reveal any hybridization signal. The results suggest an intraspecific and monophyletic origin for B chromosomes in D. sericeus, probably from the second or third autosomal pair.

C-heterochromatin and NORs distribution in karyotypes of three vespertilionid bat species from Turkey

The chromosomal banding analysis of the karyotypes of Turkish populations of Eptesicus serotinus, Nyctalus lasiopterus and Barbastellus barbastellus was performed with the use of C-banding and Ag-NOR staining. The results obtained in E. serotinus and N. lasiopterus were congruent with previous data reported from other regions. The karyotype of E. serotinus (2n = 50, NF = 52) contained a moderate amount of centromeric C-heterochromatin and a single NOR was localized in an acrocentric autosomal pairs. The karyotype of N. lasiopterus (2n = 42, NF = 54) contained a higher amount of centromeric C-heterochromatin and the NORs were localized in two autosomal pairs. The karyotype of B. barbastellus was standard in its general characteristics (2n = 32, NF = 54, low amount of C-heterochromatin) but the NOR was localized in only one acrocentric autosomal pair. In studies from other regions, the NORs were recognized in all five acrocentric autosomal pairs of the complement of B. barbastellus.

High-Resolution Physical Chromosome Mapping of Multigene Families in Lagria villosa (Tenebrionidae): Occurrence of Interspersed Ribosomal Genes in Coleoptera

The organization and mapping of multigene families can produce useful genetic markers, and its use may elucidate the mechanisms of karyotype variation and genomic organization in different groups of eukaryotes. To date, few species of Coleoptera have been analyzed using FISH for the location of multigene families. The purpose of this study was to use high-resolution chromosome mapping to establish the genomic organization of the 18S rDNA, 5S rDNA and histone H3 gene families in Lagria villosa. FISH was performed using 18S rDNA, 5S rDNA and histone H3 probes prepared via PCR labeling. Fiber-FISH for 18S and 5S rDNA indicated that both ribosomal elements are colocalized in the short arm of chromosome 4. Additionally, FISH, using the histone H3 probe, revealed that this sequence is found in only one autosomal pair and did not colocalize with rDNA. Fiber-FISH with 5S and 18S probes, used to improve the mapping resolution of these regions, showed that both genes are closely interspersed with varying amounts of both DNA classes.

Heterochromatin characterization and ribosomal gene location in two monotypic genera of bloodsucker bugs (Cimicidae, Heteroptera) with holokinetic chromosomes and achiasmatic male meiosis

Members of the family Cimicidae (Heteroptera: Cimicomorpha) are temporary bloodsuckers on birds and bats as primary hosts and humans as secondary hosts.Acanthocrios furnarii(2n=12=10+XY, male) andPsitticimex uritui(2n=31=28+X1X2Y, male) are two monotypic genera of the subfamily Haematosiphoninae, which have achiasmatic male meiosis of collochore type. Here, we examined chromatin organization and constitution of cimicid holokinetic chromosomes by determining the amount, composition and distribution of constitutive heterochromatin, and number and location of nucleolus organizer regions (NORs) in both species. Results showed that these two bloodsucker bugs possess high heterochromatin content and have an achiasmatic male meiosis, in which three regions can be differentiated in each autosomal bivalent: (i) terminal heterochromatic regions in repulsion; (ii) a central region, where the homologous chromosomes are located parallel but without contact between them; and (iii) small areas within the central region, where collochores are detected.Acanthocrios furnariipresented a single NOR on an autosomal pair, whereasP. urituipresented two NORs, one on an autosomal pair and the other on a sex chromosome. All NORs were found to be associated with CMA3bright bands, indicating that the whole rDNA repeating unit is rich in G+C base pairs. Based on the variations in the diploid autosomal number, the presence of simple and multiple sex chromosome systems, and the number and location of 18S rDNA loci in the two Cimicidae species studied, we might infer that rDNA clusters and genome are highly dynamic among the representatives of this family.

Cytological aspects of gametogenesis in two rhigonematid (Nematoda) parasites of Anadenobolus politus (Porat) (Rhinocricidae; Diplopoda) from Guadeloupe

Certain cytological aspects of gametogenesis are examined in two species of rhigonematid nematodes parasitizing the posterior gut of Anadenobolus politus (Rhinocricidae; Diplopoda) in Guadeloupe. In both species, sex is determined by an XX/XO mechanism; this is taken as an indication of the phylogenetic distinctness of rhigonematids from the order Oxyurida which recent studies show to be haplodiploid. In Ichthyocephalus anadenoboli. males had 9 and females had 10 chromosomes; in Heth mauriesi, males had 15 and females had 16 chromosomes. In both species, the X chromosome and one autosomal pair were positively heteropyenotic (i.e., they condensed before and stained more intensely than the rest of the chromosomes) during meiotic prophase in males; in H. mauriesi, these chromosomes were negatively heteropyenotic during meiotic metaphase in males. In females of both species, all chromosomes stained similarly.

An electron microscope study of the karyotypes of two wolf spiders

Meiosis in two species of wolf spiders, Lycosa georgicola Walckenaer and Lycosa rabida Walckenaer, has been analyzed by light and electron microscopy. Both karyotypes comprise 13 autosomal pairs + X1X2, all except one pair of which are telocentric. The autosomes show a gradual increase in size ranging from 5.6 to 9.9% of the total genome length. The two X chromosomes of L. rabida are not significantly different in length. In both species, the two X chromosomes are loosely aligned at prophase, but never synapse in the true sense; they do not form synaptonemal complexes. This supports the evidence that X1 and X2 are not homologous. In L. georgicola, one of the X's is associated at prophase with one autosomal pair, but this association does not persist to prometaphase.

HISTOCOMPATIBILITY STUDIES IN A CLOSELY BRED COLONY OF DOGS

The segregation of the canine DL-A leukocyte group antigen(s) b, c, d, e, f, g, h, k, l, and m has been traced in 141 consecutive matings in the Cooperstown Colony of beagles. All of the leukocyte antigen(s) were regularly transmitted en bloc from parent to offspring, with no instance of independent segregation. A total of 23 haplotypes, including six different DL-A antigen patterns (gl, bkhfm, bkcd, e, be, fgl) was observed. 31 different DL-A phenotypes were observed in a population of 100 mongrel dogs. A number of statistically significant positive and negative associations between individual DL-A antigenic components occurred in this population. The results support the concept of the DL-A system as a complex immunogenetic system governed by a single region (or locus) of an autosomal pair of chromosomes. Studies of skin, kidney, heart, and liver allografts in the Cooperstown Colony indicated that the longest allograft survivals occur under genetically and serologically defined conditions of donor-recipient DL-A compatibility. Skin and renal allografts generally behaved in parallel fashion, while cardiac allografts survived for longer periods of time (MST = 47.1 days) than kidneys (MST = 28.1 days) or skin (MST = 25.1 days) under conditions of DL-A identity. Heart transplants were rejected at a more rapid rate than kidney, however, in DL-A-incompatible donor-recipient combinations. Liver transplants were accorded the longest survival time (MST = 76.2 days) under conditions of DL-A identity, but were rejected at a rapid rate (MST = 5 days) in DL-A-incompatible nonlittermate donor-recipient pairs. The results provide further evidence that the DL-A system is the principal system of histocompatibility in the canine species. The differences in survival of different organs under similar conditions of donor-recipient DL-A compatibility suggest, however, the existence of a number of unknown variables which may also be capable of significantly affecting allograft behavior.