Novosibirsk revisited 24 years on: chromosome polymorphism in the Novosibirsk population of the common shrew Sorex araneus L

A Robertsonian fusion polymorphism in the common shrew (Sorex araneus L.), first described in Academgorodok near Novosibirsk (western Siberia) in 1970-72, was re-examined in 1994-95. The polymorphism in the 1970s involved chromosome arm combinations go, jl, mp and qr, i.e. each of these combinations was present in both a metacentric and a twin-acrocentric state in the population at that time. The twin-acrocentric morph for go occurred at low frequency in 1970-72 and was not observed in 1994-95. The polymorphism for arm combinations jl, mp and qr was still observed in 1994-95 and there was no significant difference in metacentric/twin-acrocentric frequencies compared with the previous sample. This is the third well-documented example in which the chromosome polymorphism in the common shrew has been found to be unchanged over a period of 20+ years. Although the polymorphism for qr may be associated with a chromosomal hybrid zone with a cline centre 200 km away, there is no definitive explanation for the other polymorphisms.

Localization of the genes for major ribosomal RNA on chromosomes of the house musk shrew, Suncus murinus, at meiotic and mitotic cells by fluorescence in situ hybridization and silver staining

The genes for major ribosomal RNA were localized on chromosomes 5pter-p15, 9q64-qter, and 13q38-qter of the house musk shrew, Suncus murinus (Insectivora, Soricidae) by silver staining of mitotic metaphase and meiotic pachytene spreads and fluorescence in situ hybridization using the human 28S-RNA genes as a probe to mitotic metaphase spreads. The data presented indicate a correlation between sites of in situ hybridization and silver staining. The finding of nuclear materials in mitosis was in a good agreement with observation in meiosis: same chromosomes carried active NORs in both meiotic and mitotic cells.

[Geography of chromosomes of natural populations of the shrews Sorex araneus and Suncus murinus]

The geographic distribution of chromosome races of two shrew species (Sorex araneus and Suncus murinus) was analyzed on the basis of published data and personal results. It was shown that expansion of both species was accompanied by fixation of different chromosome rearrangements (mainly Robertsonian translocations) in isolates. Chromosome polymorphism studied from the viewpoint of ecology and geography of these species allows reconstruction of their evolutionary history and understanding of the speciation process.

Robertsonian chromosomal variation in the house musk shrew (Suncus murinus, Insectivora:Soricidae) and the colonization history of the species

A high-resolution G-banding technique was used to identify five metacentrics that characterize Suncus murinus from Sri Lanka. These metacentrics were shown to be the product of Robertsonian fusion of acrocentric chromosomes identical to those in the standard karyotype defined by M.B. Rogatcheva et al. Two of the metacentrics in the Sri Lankan shrews (Rb(10.12) and Rb(14.15)) were the same as those reported by C.H. Sam et al. in Malayan populations of S. murinus. This finding provides strong support for the suggestion of T.H. Yosida that metacentric-carrying shrews colonized Malaya from Sri Lanka and hybridized with individuals of standard karyotype, generating the Robertsonian polymorphism now observed. In addition to the Robertsonian variation in S. murinus, we have used our high resolution technique (G- and C-banding) to characterize variants on chromosome 7, the X chromosome, and the Y chromosome.

Chromosome location of sixteen genes in the common shrew, Sorex araneus L. (Mammalia, Insectivora)

This report extends the genetic map of the common shrew (Sorex araneus) by use of a clone panel of shrew-Chinese hamster and shrew-mouse hybrid cells (Pack et al., 1995; Matyakhina et al., 1996). This set of hybrid clones made it possible to assign the shrew genes for isocitrate dehydrogenase 2 (IDH2), inorganic pyrophosphatase (PP), glutamicpyruvate transaminase (GPT), adenosine kinase (ADK), glucuronidase 2 (GUSB) and acid phosphatase 2 (ACP2) to chromosome ik; the genes for adenylate kinases 1 and 3 (AK1 and AK3) to chromosome af; the genes for glutamate-oxaloacetate transaminase 2 (GOT2), peptidase D (PEPD) and growth hormone (GH) to chromosome hn; the gene for phosphoglucomutase 2 (PGM2) to chromosome go, the gene for enolase 1 (ENO1) to chromosome ji, the gene for ornithine carbamoyl-transferase (OTC) to chromosome de, the gene for aminoacylase 1 (ACY1) to arm m (chromosome mp), the gene for glutamate-oxaloacetate transaminase 1 (GOT1) to arm q (chromosome qr). Thus, the genetic map of the common shrew now contains 33 genes and it is possible to compare the syntenic associations with other species.

Chromosome localization of the loci for PEPA, PEPB, PEPS, IDH1, GSR, MPI, PGM1, NP, SOD1, and ME1 in the common shrew (Sorex araneus)

This report extends the genetic map of the common shrew (Sorex araneus) by adding chromosome assignments for ten genes to the seven already mapped (Pack et al. 1995). A somatic cell hybrid panel was used for the mapping. The genes for peptidase A (PEPA) and isocitrate dehydrogenase-1 (IDH1) map to chromosome de; the genes for phosphoglucomutase-1 (PGM1), superoxide dismutase-1 (SOD1), and mannosephosphate isomerase (MPI) are located on chromosome af; the genes for nucleoside phosphorylase (NP) and glutathione reductase (GSR) are on chromosome ik; and the genes for peptidase S (PEPS), malic enzyme-1 (ME1), peptidase B (PEPB) are found on chromosomes jl, go, and mp respectively.

Chromosome localization of the gene for growth hormone in the common shrew (Sorex araneus)

The chromosome localization of the gene encoding growth hormone (GH) was determined by Southern blotting of DNA obtained from a panel of common shrew x Chinese hamster and common shrew x mouse hybrid somatic cell clones using mink GH DNA as a probe. The GH gene was found to be localized on chromosome hn of the common shrew.

Gene mapping in the common shrew (Sorex araneus; Insectivora) by shrew-rodent cell hybrids: chromosome localization of the loci for HPRT, TK, LDHA, MDH1, G6PD, PGD, and ADA

We selected the common shrew (Sorex araneus) to generate the first insectivore gene map. Shrew-Chinese hamster and shrew- mouse somatic cell hybrid cells were constructed. When the 119 shrew-rodent clones were characterized, only shrew chromosomes were found to have segregated. A panel of hybrid clones was selected for gene assignment. The genes for hypoxanthine phosphoribosyl transferase (HPRT), glucose-6- phosphate dehydrogenase (G6PD), and malate dehydrogenase 1 (MDH1) were assigned to shrew Chromosome (Chr) de [which is the product of a tandem fusion between the 'original' mammalian X Chromosome (Chr) and an autosome], the gene for adenosine deaminase (ADA) and 6-phosphogluconate dehydrogenase se (PGD) to Chromosome jl, the gene for thymidine kinase (TK) to Chromosome hn, and the gene for lactate dehydrogenase (LDHA) to chromosome ik. Further studies in progress.

Recombination in single and double heterozygotes for two partially overlapping inversions in chromosome 1 of the house mouse

Recombination frequency, chiasmata and chromatid interference were studied by means of analysis of meiotic configurations in diakinesis and metaphase II in single and double heterozygotes for the partially overlapping inversions In(1)1Rk and In(1)12Rk in chromosome 1 of the house mouse. Recombination frequency in the inverted regions was decreased in single heterozygotes and increased in the double heterozygotes as compared to normal homozygotes. Chiasmata in the inverted regions in the double heterozygotes did not interfere with each other. A significant excess of 4-chromatid double exchanges in the inverted regions was detected in the double heterozygotes.

Radioadaptive response in primary mouse spermatocytes revealed by analysis of synaptonemal complexes

This study was aimed at estimating the damage to the synaptonemal complex (SC) of male mice caused by radiation exposure at the ultimate pre-meiotic interphase. Four experimental groups were formed: group 1 was an untreated control, group 2 received a low dose (50 mGy) of radiation, group 3 a high dose (4 Gy) of radiation, group 4 was first treated with a low dose (50 mGy) and 4 h later with a high dose (4 Gy). Mice were killed 4 days after the treatment. Early pachytene cells were selected for the electron microscopic analysis of SCs. These cells were supposed to be at pre-meiotic interphase at the time of irradiation. Treatment with a low dose of radiation did not produce any substantial increase in the frequency of SC aberrations, while exposure to the high dose resulted in various types of damage. Group 4 demonstrated significantly lower frequencies of axial breaks/fragments and multiaxial configurations than group 3. At the same time, these two groups did not differ in the frequencies of inter- and intrachromosomal exchanges such as translocations, inversions, and deletions. We suppose that the number of breaks produced by a high dose of radiation was the same in the both groups. However, a proportion of the breaks that remained unrepaired until pachytene and were expressed as gaps, fragments, and multiaxial configurations was reduced by pretreatment with the low dose of radiation.

[Meiotic crossing over--not the only source of recombinants in man]

On the basis of chiasma distributions along bivalents in human male meiosis, genetic lengths were counted for several chromosomal segments. These estimates appeared to be lower than the corresponding genetic lengths produced in the recombination analysis. When al so cytological distances and number of markers used in multilocus mapping were taken into account, the regression estimates of genetic lengths were shown to satisfactorily fit the observed values. This indicates that mitotic crossingover, genetic conversion, mutation and errors in allel's identification in addition to meiotic crossingover, appear to contribute to the observed genetic maps. It is suggested that these namely events, rather than the typing errors suggested by Morton (1991), seem observed over those predicted on the basis of chiasma counts.

Chiasma distribution in the first bivalent of mice carrying a double insertion of homogeneously-staining regions in homo- and heterozygous states

An examination of the meiotic pattern of chromosome 1 isolated from a feral mouse population and containing a double insertion (Is) of homogeneously-staining regions (HSRs) was carried out. In a previous study is was shown that the region delineated by the proximal breakpoint of Is(HSR;1C5) 1Icg and the distal one of Is(HSR;1D)2Icg is unpaired during early pachytene and heterosynapsed at midpachytene. No synaptic disturbances were revealed in homozygotes in this study. Chiasmata number per first bivalent in heterozygous (1.87) and homozygous (1.88) males was shown to be higher than in normal ones (1.61). In normal males a single chiasma is located in the medial part of chromosome 1. In heterozygotes this segment is heterosynapsed and unavailable for recombination. This leads to a significant decrease in the frequency of bivalents bearing a single chiasma and an increase in the frequency of bivalents bearing double chiasmata located mostly at subcentromeric and subtelomeric regions of the chromosome. In homozygous males the frequency of double chiasmata is also increased, and even triple chiasmata become possible because of the increase in the physical length of the bivalents. Thus insertion of heterochromatic regions, which are inert with respect to recombination, leads to an increase in the length of the genetic map of the chromosome because of relaxation of interference restrictions.

The X-autosome translocation in the common shrew (Sorex araneus L.): late replication in female somatic cells and pairing in male meiosis

Common shrews have an XX/XY1Y2 sex chromosome system, with the "X" chromosome being a translocation (tandem fusion) between the "original" X and an autosome; in males this autosome is represented by the Y2 chromosome. From G-banded chromosomes, the Y2 is homologous to the long arm and centromeric part of the short arm of the X. The region of the X that is homologous to the Y2 and also the telomeric region of the short arm of the X were found to be early replicating in somatic cells from a female shrew after 5-bromo-2'-deoxyuridine (BrdU) treatment in vitro. The remainder of the short arm of the X was shown to be late replicating. Electron microscopic examination of synaptonemal complexes in males at pachytene revealed pairing of the Y2 axis with the long arm of the X, and Y1 with the short arm. At early stages of pachytene, there is apparently extensive nonhomologous pairing between the X and Y1. In essence, the short arm of the shrew X chromosome behaves like a typical eutherian X chromosome (it is inactivated in female somatic cells and is paried with the Y1 during male meiosis) while the long arm behaves like an autosome (escapes the inactivation and pairs with the Y2).

[An unusual heteromorphic bivalent in the common vole (Microtus arvalis) from Byelarus]

Electron microscopic analysis was carried out on the synaptonemal complexes of ten male common voles (Microtus arvalis) caught of 1990 in Byelorussia. In the early pachytene stage of spermatocytes of four males heteromorphic bivalent has been found in one of five large autosomes. In the central region of the bivalent one of the lateral elements is in the form of a D-loop, characteristic of insertion/deletion heterozygotes. However, high-resolution G-band staining of mitotic chromosomes from fibroblasts showed no significant differences in the G-band patterns between homologues.

Sexual maturation and seasonal changes in plasma levels of sex steroids and fecundity of wild Norway rats selected for reduced aggressiveness toward humans

Parameters of sexual maturation and reproductive function were compared in two groups of Norway rats, one selected for reduced aggressiveness towards man and the other for aggressiveness. It was found that selection for reduced aggressiveness produced an acceleration of sexual maturation as judged by earlier vaginal opening in the female and presence of mature spermatozoa in the testes of the male as well by earlier prepubertal increase in plasma testosterone in the male. In domesticated adults, seasonal variations in the parameters of the reproductive function narrowed; they showed neither the winter decrease in sexual activity nor the marked fall in plasma testosterone and estradiol exhibited by their aggressive counterparts.

Synaptic interrelationships between the segments of the heteromorphic bivalent in double heterozygotes for paracentric inversions in chromosome 1 of the house mouse

Electron microscopic analysis of synaptonemal complexes in double heterozygotes for the partially overlapping inversions In(1)1Rk and In(1)12Rk in chromosome 1 of the house mouse was carried out. A great variety of synaptic configurations with complicated combinations of homologously and non-homologously paired segments was observed. Analysis of these configurations revealed at least five independent pairing regions in chromosome 1. Interrelationships between these regions with respect to their pairing ability were estimated. Pairings in the distal non-inverted segment and in inversions inhibit each other, while pairing in either inverted segment facilitates synapsis in the other. In other words, pairing initiations in different parts of the same bivalent are not independent events.

Unusual heteromorphic bivalents in the common vole (Microtus arvalis) from Belorussia

Electron microscopic analysis was carried out on the synaptonemal complexes of 10 male common voles (Microtus arvalis) caught in 1990 in Belorussia. In the early pachytene stage of spermatocytes of four males, a heteromorphic bivalent has been found in one of five large autosomes. In the central region of the bivalent one of the lateral elements is in the form of a D-loop, characteristic of insertion/deletion heterozygotes. However, high-resolution G-band staining of mitotic chromosomes from fibroblasts shows no significant differences in the G-band pattern between homologs.

Chromosome pairing and recombination in mice heterozygous for different translocations in chromosomes 16 and 17

In order to clarify the relationship between meiotic pairing and recombination, an electron microscopic (EM) study of synaptonemal complexes (SC) and an analysis of chiasma frequency and distribution were made in male mice singly and doubly heterozygous for Robertsonian [Rb(16.17)7Bnr] and reciprocal [T(16:17)43H] translocations and also in tertiary trisomics for the proximal region of chromosome 17. In all these genotypes an extensive zone of asynapsis/desynapsis around the breakpoints was revealed. At the same time a high frequency of non-homologous pairing was observed in precentromeric regions of acrocentric chromosomes. The presence in the proximal region of chromosome 17 of the t haplotype did not affect the synaptic behaviour of this region. Chiasma frequency in the proximal region of chromosome 17 in the T(16:17)43H heterozygotes and trisomics was increased when compared with that in Robertsonian heterozygotes.

Positional control of chiasma distribution in the house mouse. Chiasma distribution in mice homozygous and heterozygous for an inversion in chromosome 1

An examination of the chiasma distribution in chromosome 1 of male mice homozygous and heterozygous for a distal inversion In(1) 12Rk and in normal males was carried out. No differences in chiasma distribution were found between homozygotes for the inversion and homozygotes for normal chromosome 1. A significant decrease in the frequency of bivalents bearing chiasmata in the pretelomeric region was found in heterozygotes. This, in its turn, produced a redistribution of chiasmata in the proximal non-inverted part of bivalent 1. These results could be interpreted as evidence for positional control of the chiasma distribution pattern: the distance of certain parts of the chromosome from the telomere and chiasmata interference are more important for determination of the chiasma frequency in a given region than its genetic content.

A case of spontaneous trisomy in the spermatocytes of Microtus arvalis

A triple synaptomal complex was observed between 3 small-sized chromosomes in 4 spermatocytes closely connected by intercellular bridges, of the common vole (Microtus arvalis L.). Other spermatocytes from the same and from 2 other males had a normal chromosome complement and pairing patterns. This finding was interpreted as the result of a single act of non-disjunction taking place in a spermatogonium. These data suggest that chromosome non-disjunction in premeiotic germ cells can be considered one of the causes of aneuploidy in mammals.

Synaptonemal complexes of the common shrew, Sorex araneus L., in spermatocyte spreads

This paper presents an electron microscopic analysis of the behavior and morphology of the sex chromosomes and autosomes during prophase I in the common shrew, Sorex araneus L. The pairing patterns of the X/Y1Y2 and autosomal Robertsonian trivalents are described.

The origin of a double insertion of homogeneously staining regions in the house mouse (Mus musculus musculus)

A high resolution analysis of the G-band patterns of normal and aberrant chromosomes 1, bearing two linked insertions of homogeneously staining regions (HSRs) in the house mouse (Mus musculus musculus) reveals the inverted pattern of the euchromatic region between the HSRs. On the basis of this analysis a hypothesis on the origin of the aberrant chromosome is put forward: the double insertion is a result of an inversion of the chromosome 1 of Mus musculus domesticus bearing a single insertion of HSR. The proximal breakpoint is localized inside the HSR, and the distal one between subbands E3 and E4.

Synapsis in single and double heterozygotes for partially overlapping inversions in chromosome 1 of the house mouse

Electron microscopic (EM) 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 chromosome 1 of the house mouse reveals that synapsis and synaptic adjustment are dependent on the size and location of the inversions and interaction between the latter. Is(1)1Icg contains insertions of the inverted repeats Is(HSR;1C5)1Icg and Is(HSR;1D)2Icg and an inverted euchromatic region. Synaptic adjustment of the D-loops by shortening of the asynapsed segments of the lateral elements belonging to the insertions occurs at the late zytogene to early pachytene stage. Synaptic adjustment of the inversion loops takes place at early to late pachytene. A delay in adjustment was found in the double heterozygotes In(1)1Icg/In(1)1Rk and In(1)1Icg/In(1)12Rk. A correspondence between the lifespan of asynapsis in inverted regions and the probability of association of XY and heteromorphic bivalents was revealed.