[Genetic control of chromosome synapsis in mice heterozygous for a paracentric inversion].

Frequencies of formation of inversion loops and their relative sizes were studied in laboratory mice heterozygous at paracentric inversion In1(1)Rk in chromosome 1, depending on the genetic background. Homozygotes In1/In1 were crossed with mice from five inbred strains (A/HeJ, BALB/cJ, C3H/HeJ, C57BL/6J, DBA2/J). The frequency of formation of inversion loops, their relative sizes, and the dependence of these parameters on the stage of pachitene were analyzed on electron-microscopic slides of spread spermatocytes in first-generation hybrids. It was shown that the genetic background and cross direction statistically significantly influenced the duration of individual pachitene stages and the frequency of inversion loops, but not relative loop size. Using a database on SNP distribution in the inbred strains examined, we carried out in silico mapping of genes affecting the genotype-dependent characters. We have found that the efficiency of synapsis in the inversion does not depend on interstrain differences in homology of the chromosome 1 region involved in the inversion. Genes controlling the inversion loop frequency in the inversion heterozygotes were mapped to chromosome 7, and genes controlling the duration of individual pachitene stages, to chromosomes 2 and 5.

[Chromosomal evolution of the Common Shrew Sorex araneus L.from the Southern Ural and Siberia in the postglacial period]. / Khromosomnaia évoliutsiia obyknovennoi burozubki Sorex araneus L. v poslelednikovoe vremia na Iuzhnom Urale i v Sibire.

This paper summarizes a series of studies on chromosomal geography of the common shrew Sorex araneus L. in Siberia and the Southern Urals. Chromosomal races inhabiting the Southern Urals and the Western Siberian Plain sequentially replace each other in the latitudinal direction. In this region, karyotypes of each two adjacent races differ from each other by a single whole-arm reciprocal translocation. In the Eastern Siberian branch, the neighboring races differ mainly in the number or set of metacentric chromosomes. Analysis of the race distribution in the common shrew in the context of paleophysiology of the glacial period allowed us to reconstruct the sequence of events leading to the establishment of the present-day structure of the species.

[Positional control of the distribution of spontaneous sister chromatid exchanges along mouse chromosomes]. / Pozitsionnyi kontrol' raspredeleniia spontannykh sestrinskikh khromatidnykh obmenov po khromosomam myshi.

The use of a new method having combined C-band staining and differential staining of sister chromatids allowed to determine a pattern of distribution of spontaneous sister chromatid exchanges (SCE) along cytologically marked chromosomes 1, 2 and 6 of house mouse. All chromosomes displayed the same pattern of SCE distribution: SCEs are most frequent in the middle part of the chromosome arm and rather rare near the centromere and the telomere. It has been suggested that this pattern of distribution is positional, rather chromatin-specific. The chromosome 1 carrying paracentric inversion with breakpoints in the middle part of the arm and just near the telomere has the same pattern of SCE distribution as normal chromosome 1. Double insertion of homogeneously staining regions in the middle part of the chromosome 1 produces increase in the SCE number per chromosome proportional to the physical length of the insertion. In contrast to meiotic recombination, interference between SCEs is not detected. No evidence for existence of the hot-spots of SCE on the junctions between C-positive and C-negative regions, as well as between G-bands and R-bands, has been produced.

[Chromosomal control of chiasma distribution in house mice. Analysis of chiasma distribution in homo- and heterozygotes by inversion in chromosome 1]. / Khromosomnyi kontrol' raspredeleniia khiazm u domovoi myshi. Analiz raspredeleniia khizm u gomo- i geterozigot po inversii v 1-i khromosome.

Examination of chiasma distribution in the chromosome 1 in male mice homo- and heterozygous for distal inversion In(1)12Rk and in normal mice was carried out. No differences in chiasma distribution was found between homozygotes for the inversion and homozygotes for normal chromosome 1. A drastic change in this trait was revealed in heterozygous animals. In heterozygotes, the telomeric segments of SC were asynapsed and unavailable for recombination. This leads to significant decrease in the frequency of bivalents bearing chiasmata in pretelomeric region. In turn, it produced chiasma redistribution in proximal noninverted portion of the bivalent 1. These results could be interpreted as evidence for chromosomal control of chiasma distribution pattern: the distance of certain part of the chromosome from telomere and interference (which also operates at the chromosomal level) are more important for determination of the chiasmata frequency in the given region, than its genetic content.

[Synapsis in single and double heterozygotes for partially overlapping inversions in chromosome 1 of the house mouse]. / Sinapsis u odinochnykh i dvoinykh geterozigot po chastichno perekryvaiushchimsia inversiiam v pervoi khromosome domovoi myshi.

Electron microscopic analysis of synaptonemal complexes (SC) in single and double heterozygotes for the partially overlapping inversions In(1)1Icg, In(1)1Rk and In(1)12Rk in the Chromosome 1 of the house mouse reveals a dependence of synapsis and synaptic adjustment on the size and location of the inversions and their interaction. In(1)1Icg contains the insertions of inverted repeats Is(HSR: 1C5)1Icg and Is(HSR: 1I)2Icg as well as inverted euchromatic region. The synaptic adjustment of the D loops by shortening of asynapsed parts of the lateral elements of SC belonging to the insertions occurs at late zygotene-early pachytene stage. After that the synaptic adjustment of the inversion loops takes place. A delay in adjustment was found in diheterozygotes In(1)1Icg/In(1)1Rk and In(1)1Icg/In(1)12Rk. Morphological alterations of the asynapted terminal segments of lateral elements preventing synaptic adjustment were found in single and double heterozygotes for In(1)1Rk and In(1)12Rk. Correspondence between the size of asynapted regions and the probability of association of XY and heteromorphic bivalents was revealed.

[Synapsis and recombination of chromosomes in the house mouse homozygous for the double inversion of the homogeneously stained regions in chromosome 1]. / Sinapsis i rekombinatsiia khromosom u gomozigot po dvoinoi inversii gomogenno okrashivaemykh raionov v 1-i khromosome domovoi myshi.

Examination of the meiotic pattern of chromosome 1 isolated from feral mouse population and containing a double insertion (Is) of homogeneously staining regions (HSRs) was carried out. In the previous study it has been shown that the region delineated by the proximal break point of Is(HSR; 1C5) 1Icg and the distal one of Is(HSR; 1E3) 2Icg is desynapsed during early pachytene and heterosynapsed at midpachytene. No synaptic disturbances were revealed in homozygotes in this study. Chiasma frequency in hetero- (1.87) and in homozygous (1.88) males was shown to be higher than in normal ones (1.61). Thus, insertion of recombinationally inert heterochromatic regions leads to increase in the length of genetic map of the chromosome via physical elongation and relaxation of interferential restrictions.

[The causes of appearance of a double insertion of homogeneously staining regions in the chromosome 1 of house mouse (Mus musculus musculus)]. / Prichiny vozniknoveniia dvoinoi insertsii gomogenno okrashivaemykh raionov v 1-i khromosome domovoi myshi (Mus musculus musculus).

A high resolution analysis of G-band pattern of normal and aberrant chromosome 1 bearing two linked insertions of homogeneously staining regions (HSRs) in the house mouse (Mus musculus musculus) reveals an inverted pattern of the euchromatic region between the HSRs. On the basis of this analysis, a hypothesis on the causes for appearance of the aberrant chromosome was put forward: the double insertion is a result of inversion of the chromosome 1 of Mus musculus domesticus bearing a single long insertion. The proximal breakpoint is localized inside the HSR and the distal one--between subbands E3 and E4. From the point of view of these data, new symbols for the aberrations are proposed: Ls (HSR, 1C5) 1Icg--for the proximal insertion, Is(HSR, 1D)21cg--for the distal one, In (1) 1Icg--for the inverted region, including the bands D, E1-E3 and the insertion Is(HSR 1D)21cg.

[Effect of heterozygosity for insertions of homogeneously stained regions in chromosome 1 of the house mouse on synapsis in meiotic prophase]. / Vliianie geterozigotnosti po insertsiiam gomogenno okrashivaemykh raionov v 1-i khromosome domovoi myshi na sinapsis v profaze meioza.

Electron microscope analysis of surface-spread synaptonemal complexes (SC) in oocytes and spermatocytes from double cis heterozygotes for Is(HSR; 1C5)1Icg and Is(HSR; 1E3)2Icg was carried out. Aberrant chromosomes were isolated from the feral population of Mus musculus musculus of Novosibirsk. They contain homogeneously stained regions of total length of about 30% of Chr 1 mitotic metaphase. Heteromorphic bivalents of Chr1 with different lengths of the lateral elements of SC and the loop in the intermedial position were revealed in 4.4% spermatocytes and 20% oocytes of heterozygous animals. The loop size depends on the stage of meiosis: it is maximal at late zygotene and decreases up to disappearance during pachytene.

[Effect of double insertion of homogeneously stained regions in chromosome 1 of the house mouse on recombination frequency]. / Vliianie dvoinoi insertsii gomogenno okrashivaemykh raionov v 1-i khromosome domovoi myshi na chastotu rekombinatsii.

By means of genetic and cytogenetic analysis, the effect of cis heterozygosity for two insertions--Is(HSR; 1C5)1Icg and Is (HSR; 1E3)2Icg was studied. It was shown that the proximal point of Is is situated 8 cM distally from the ln gene. Crossing over is completely suppressed in the intermedial part of Chr. 1, where a single chiasma appears in normal mice. The frequency of double chiasmata in heterozygotes is significantly increased. They are localized at precentromeric and pretelomeric parts of Chr. 1. It is supposed that recombination block in the central region leads to a shift of the potential chiasmata in telomeric regions. This shifted telomeric chiasmata, in turn, allow the appearance of the second chiasmata in the centromeric region.