Germline-restricted chromosomes (GRCs) are present in the genomes of germline cells and absent from somatic cells. A GRC is found in all species of the songbirds (Passeri) and in none of the other ...bird orders studied to date. This indicates that GRC originated in the common ancestor of the songbirds. The germline-restricted chromosome is permanently absent from somatic cells of the songbird, while female germline cells usually contain two copies of GRC and male ones have one copy. In females, GRCs undergo synapsis and restricted recombination in their terminal regions during meiotic prophase. In males, it is almost always eliminated from spermatocytes. Thus, GRC is inherited almost exclusively through the maternal lineage. The germline-restricted chromosome is a necessary genomic element in the germline cells of songbirds. To date, the GRC genetic composition has been studied in four species only. Some GRC genes are actively expressed in female and male gonads, controlling the development of germline cells and synthesis of the proteins involved in the organization of meiotic chromosomes. Songbird species vary in GRC size and genetic composition. The GRC of each bird species consists of amplified and modified copies of genes from the basic genome of that species. The level of homology between GRCs of different species is relatively low, indicating a high rate of genetic evolution of this chromosome. Transmission through the maternal lineage and suppression of the recombination contribute significantly to the accelerated evolution of GRCs. One may suggest that the rapid coordinated evolution between the GRC genes and the genes of the basic genome in the songbirds might be responsible for the explosive speciation and adaptive radiation of this most species-rich and diverse infraorder of birds.
The avian leukosis virus (ALV) is a serious threat to sustainable and economically viable commercial poultry management world-wide. Active infections can result in more than 20% flock loss, resulting ...in significant economic damage. ALV detection and elimination from flocks and breeding programs is complicated by high sequence variability and the presence of endogenous virus copies which show up as false positives in assays. Previously-developed approaches to virus detection are either too labor-intensive to implement on an industrial scale or suffer from high false negative or positive rates. We developed a novel multi-locus multiplex quantitative real-time PCR system to detect viruses belonging to the J and K genetic subgroups that are particularly prevalent in our region. We used this system to eradicate ALV from our broiler breeding program comprising thousands of individuals. Our approach can be generalized to other ALV subgroups and other highly genetically diverse pathogens.
The last decade was marked by a steep rise in avian studies at genomic and cellular levels. Cell lines are important tools for in vitro studies in cell biology and cytogenetics. We developed a simple ...method of primary somatic cell culture establishment from the ovaries of the great tits (Parus major) and testes of ten Passerine species, characterized the cellular composition of the ovary-derived lines using RT-PCR and immunolocalization of the tissue-specific markers and tested the efficiency of two methods of genetic transformation of the ovary-derived cell line. We found that the ovary-derived cell cultures of the great tit were composed of fibroblasts mainly, but also contained interstitial and granulosa cells. They were cultivated until the 10th passage without any noticeable decrease in their proliferative activity. The testis-derived cell cultures had lower proliferative potential. However, both ovary- and testis-derived cell cultures provided enough material for high quality mitotic metaphase chromosome preparations. The efficiency of its transduction with lentivirus containing a GFP reporter was very low, while electroporation with episomal vectors expressing GFP resulted in a high yield of GFP-positive cells. The proposed method could be used for the generation of high quality material for various cytogenetic and genomic studies.
The formation of hybrid sterility is an important stage of speciation. The voles of the genus
Microtus
, which is the most speciose genus of rodents, provide a good model for studying the cytological ...mechanisms of hybrid sterility. The voles of the “
mystacinus
” group of the subgenus
Microtus
(2
n
= 54) comprising several recently diverged forms with unclear taxonomic status are especially interesting. To resolve the taxonomic status of
Microtus mystacinus
and
Microtus kermanensis
, we crossed both with
Microtus rossiaemeridionalis
, and
M. kermanensis
alone with
Microtus arvalis
“obscurus” and
M. transcaspicus
and examined the reproductive performance of their F1 hybrids. All interspecies male hybrids were sterile. Female
M. kermanensis
×
M. arvalis
and
M. kermanensis
×
M. transcaspicus
hybrids were sterile as well. Therefore,
M. mystacinus
,
M. kermanensis
, and
M. rossiaemeridionalis
could be considered valid species. To gain an insight into the cytological mechanisms of male hybrid sterility, we carried out a histological analysis of spermatogenesis and a cytological analysis of chromosome synapsis, recombination, and epigenetic chromatin modifications in the germ cells of the hybrids using immunolocalization of key meiotic proteins. The hybrids showed wide variation in the onset of spermatogenesis arrest stage, from mature (although abnormal) spermatozoa to spermatogonia only. Chromosome asynapsis was apparently the main cause of meiotic arrest. The degree of asynapsis varied widely across cells, individuals, and the crosses—from partial asynapsis of several small bivalents to complete asynapsis of all chromosomes. The asynapsis was accompanied by a delayed repair of DNA double-strand breaks marked by RAD51 antibodies and silencing of unpaired chromatin marked by γH2A.X antibodies. Overall, the severity of disturbances in spermatogenesis in general and in chromosome synapsis in particular increased in the hybrids with an increase in the phylogenetic distance between their parental species.
Chromosomal races of the common shrew differ in sets of metacentric chromosomes and on contact may produce hybrids with extraordinarily complex configurations at meiosis I that are associated with ...reduced fertility. There is an expectation that these may be some of the most extreme tension zones available for study and therefore are of interest as potential sites for reproductive isolation. Here, we analyse one of these zones, between the Novosibirsk race (characterized by metacentrics go, hn, ik, jl, mp and qr) and the Tomsk race (metacentrics gk, hi, jl and mn and acrocentrics o, p, q and r), which form hybrids with a chain-of-nine (CIX) and a chain-of-three (CIII) configuration at meiosis I. At the Novosibirsk-Tomsk hybrid zone, the CIX chromosomes form clines of 8.53 km standardized width on average, whereas the cline for the CIII chromosomes was 52.83 km wide. The difference in these cline widths fits with the difference in meiotic errors expected with the CIX and CIII configuration, and we produce estimates of selection against hybrids with these types of configurations, which we relate to dispersal and age of the hybrid zone. The hybrid zone is located at the isocline at 200 m altitude above sea level; this relationship between the races and altitude is suggested at both coarse and fine scales. This indicates adaptive differences between the races that may in turn have been promoted by the chromosome differences. Thus, the extreme chromosomal divergence between the Novosibirsk and Tomsk may be associated with genic differentiation, but it is still striking that, despite the large chromosomal differences, reproductive isolation between the Novosibirsk and Tomsk races has not occurred.
Heterochiasmy, a sex-based difference in recombination rate, has been detected in many species of animals and plants. Several hypotheses about evolutionary causes of heterochiasmy were proposed. ...However, there is a shortage of empirical data. In this paper, we compared recombination related traits in females and males of the barn swallow Hirundo rustica (Linnaeus, 1758), the species under strong sexual selection, with those in the pale martin Riparia diluta (Sharpe and Wyatt, 1893), a related and ecologically similar species with the same karyotype (2N = 78), but without obvious sexual dimorphism. Recombination traits were examined in pachytene chromosome spreads prepared from spermatocytes and oocytes. Synaptonemal complexes and mature recombination nodules were visualized with antibodies to SYCP3 and MLH1 proteins, correspondingly. Recombination rate was significantly higher (p = 0.0001) in barn swallow females (55.6 ± 6.3 recombination nodules per autosomal genome), caused by the higher number of nodules at the macrochromosomes, than in males (49.0 ± 4.5). They also showed more even distribution of recombination nodules along the macrochromosomes. At the same time, in the pale martin, sexual differences in recombination rate and distributions were rather small. We speculate that an elevated recombination rate in the female barn swallows might have evolved as a compensatory reaction to runaway sexual selection in males.
In the Victorian era, Sir Francis Galton showed that 'when dealing with the transmission of stature from parents to children, the average height of the two parents, ... is all we need care to know ...about them' (1886). One hundred and twenty-two years after Galton's work was published, 54 loci showing strong statistical evidence for association to human height were described, providing us with potential genomic means of human height prediction. In a population-based study of 5748 people, we find that a 54-loci genomic profile explained 4-6% of the sex- and age-adjusted height variance, and had limited ability to discriminate tall/short people, as characterized by the area under the receiver-operating characteristic curve (AUC). In a family-based study of 550 people, with both parents having height measurements, we find that the Galtonian mid-parental prediction method explained 40% of the sex- and age-adjusted height variance, and showed high discriminative accuracy. We have also explored how much variance a genomic profile should explain to reach certain AUC values. For highly heritable traits such as height, we conclude that in applications in which parental phenotypic information is available (eg, medicine), the Victorian Galton's method will long stay unsurpassed, in terms of both discriminative accuracy and costs. For less heritable traits, and in situations in which parental information is not available (eg, forensics), genomic methods may provide an alternative, given that the variants determining an essential proportion of the trait's variation can be identified.
Negative heterosis can occur on different economically important traits, but the exact biological mechanisms of this phenomenon are still unknown. The present study focuses on determining the genetic ...factors associated with negative heterosis in interspecific hybrids between domestic sheep (
) and argali (
). One locus (rs417431015) associated with viability and two loci (rs413302370, rs402808951) associated with meat productivity were identified. One gene (
) was prioritized for viability and three for meat productivity (
and
). The loci associated with meat productivity were demonstrated to fit the overdominant inheritance model and could potentially be involved int negative heterosis mechanisms.
We report the features of domain growth during e-beam recording on non-polar Y-surfaces of LiNbO3 crystals doped with titanium at various concentrations (CTi). The nominally pure LiNbO3 of the ...congruent composition (CLN), LiNbO3 doped with 0.5 mol% TiO2 (CLN-0.5Ti), and the Ti:LiNbO3 planar waveguide formed as a result of high-temperature diffusion of titanium were comparatively studied. The titanium concentration at the surface of Ti: LiNbO3 was ∼7.6 at%, then CTi gradually decreased to 0.5-0.8 at% t a depth of ∼4-5 m. The combination of the etching technique with non-destructive methods of observation of the created domain structures of a planar type (low-voltage SEM and SHG microscopy) made it possible to detect the effect of titanium concentration on the features of the domain growth. It has revealed that the domain sizes and the average rate of their frontal growth (Vf) in CLN and CLN-0,5Ti are different. The observed differences are discussed in the framework of the current model of the intrinsic defect structure of LiNbO3. A peculiar three-dimensional structure of domain gratings in the Ti:LiNbO3 over the waveguide depth was found. The differences in the formation of the upper and lower parts of periodic gratings in Ti:LiNbO3 are explained by a significant increase in conductivity near the surface of the waveguide in comparison with deeper layers. The obtained results are useful to match the position and design of planar domain gratings in Ti:LiNbO3 optical waveguides on non-polar surfaces for better conversion efficiency of integrated nonlinear devices based on quasi-phase-matching.
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