Biomedical subjects
Publications and source records attributed to L D Safronova.
Blot-hybridization analysis with the use of the t-specific probe D17Leh66 has been used to study DNA of various representatives of family Muridae. Hamsters from genus Phodopus have no homologs of this probe, whereas African rats from genus Lophuromys have some homologous elements. This indicates that sequence Dl7Leh66 is ancient and was probably present in the common ancestor of family Muridae.
A new natural haplotype, twWP1, found in a population of house mouse Mus domesticus from Peru, was subjected to genetic and molecular analyses. Experiments were performed to study the complementation of the new haplotype, fertility of twMP1/tx heterozygotes, and transmission ratio distortion (TRD) of the t-carrying chromosome in the progeny of heterozygous males. Molecular analysis included blot hybridization with t-specific probes Tu48, Tu66, and Tu119. The results were collated with the structure and properties of the t complex, and the new haplotype was identified as a complete lethal one.
Mouse t-complex located on chromosome 17 contains genes affecting solely male fertility. Some genes of this complex are recessive lethals; nonetheless, the high frequency of the t-complex carriers in a population is maintained due to a mechanism referred to as transmission ratio distortion (TRD), i.e., after crosses with wild-type females, males heterozygous for the t-complex transmit the t-bearing chromosome to nearly all their offspring, which suggests that the t-complex genes control sperm function. Analysis of this phenomenon shows that the resultant TRD is determined by the ratio between the distorter genes (Tcd) and a responder gene (Tcr) located within the t-complex region. Many authors believe that two to six distorter genes currently known have an additive effect. A genetic model of the non-Mendelian inheritance in the progeny of heterozygous male mice specifically explains sterility of animals carrying the t-complex with complementary lethal genes. The model suggests that some distorter gene products interacting with the responder gene have a selective effect on motility of both mutant and wild-type sperm. Insufficient sperm motility and/or their unsuccessful capacitation result in poor if any fertilization. Information on the t-complex genes is necessary for understanding the biological mechanisms of male sterility and may be used in medical practice.
Modern data on the structure and evolution of the t complex are discussed. The t complex is a series of inversions in the proximal region of murine chromosome 17; it contains a set of genes that determine its predominant transmission to the offspring of heterozygous males. Variants of structural organization of this genetic system (t haplotypes) have been found in wild populations of four species of genus Mus (M. domesticus, M. musculus, M. molossinus, and M. castaneus), but not in representatives of other, evolutionarily remote species of this genus. The so-called vertical, horizontal, and introgressive hypotheses are discussed of the origin and evolution of the t complex. Based on population genetic studies and molecular analysis a new hypothesis on the origin of the t-complex is put forward. This hypothesis is a synthesis between the vertical and horizontal models and assumes that all known t haplotypes had a common ancestral chromosome 17 carrying a proximal inversion.
Spermatocytes of fertile, subfertile, and sterile hamster hybrids obtained by backcrossing Phodopus sungorus and Ph. campbelli were analyzed under light and electron microscopes. Light microscopy showed that early meiosis was blocked in pachitene in the spermatocytes of sterile hybrids. The X and Y chromosomes were dissociated in metaphase I in several fertile and subfertile animals. Electron microscopic analysis of the synaptonemal complex (SC) revealed a disturbed synapsis of sex chromosomes and autosomes in all hybrids. Dissociation of the sex chromosomes, terminal and interstitial asynapsis, and interlocking of autosomes were observed. Disturbed synapsis in hybrids was assumed to result from the difference between Ph. sungorus and Ph. campbelli in not only their chromosomes, but their genes as well.
Explore the source record for details and available documents.
To study the effect of a high radiation background on the structure and function of the T-complex, we used laboratory mice carrying t-haplotypes of four complementation groups (t0, t12, tw1, and tw5). In 1987-1989, the animals were kept each year for a month within a 30-kilometer zone of Chernobyl Nuclear Power Station in regions with different degrees of pollution. Subsequent genetic analysis revealed a decrease in fertility, fecundity, and the index of preferable transmission of t-carrying chromosomes in radiated animals and some of their progeny. The effect of different radiation doses on these parameters was different in animals with various t-haplotypes. A lack of complementation or a decrease in the complementation effect was revealed in a number of crosses involving the progeny of irradiated animals. The frequency of complementation distortion was about 8 x 10(-2), which is more than an order higher than the usual recombination frequency characteristic of these t-haplotypes.
The results of genetic and molecular analysis of new recombinant mouse haplotypes tM8 and tM9, derived from tw12 and t12, are described. Data on viability and fertility of tM/tM homozygotes are presented, as well as that on t-chromosome transmission ratio distortion (TRD) in the progeny of heterozygous males. Blot-hybridization analysis was performed using four t-specific probes: Tu48, Tu66, Tu119, and Tu122. Comparison of data obtained in the study with that on the structure of the initial haplotypes suggests that both recombinant haplotypes resulted from unequal crossing-over. In the case of tM9 haplotype, the crossing-over site was probably located in the region of distal t complex inversion, and tM8 haplotype resulted from two crossing-over events in the medial part of t complex.
To study structural organization and polymorphism of the proximal part of chromosome 17, a hybridization analysis of DNA from mice of different origin was carried out using four t-specific probes. Results of the analysis allow us to conclude that the DNA element copy number is quantitatively unstable and differs in distribution in both newly formed recombinant haplotypes and in wild-type chromosome 17. probe Tu66 was used to study D17Leh66-element organization of Mus abbotti and Mus hortulanus mice. Three types of D17Leh66-elements were identified in the genomes of these species. The copy number of each type of DNA element varied in the genome of each of four studied species. Homologs to t-specific Tu66 and Tu119 probes were found in the genome of Rattus norvegicus rat. The data obtained are discussed with respect to the evolution of the proximal part of Mus mouse chromosome 17.
t-complex typical feature of the house mouse 17th chromosome is the high transmission (up to 90-95%) of t-carrying chromosome to heterozygous +/t male offspring. The influence of Robertsonian translocation Rb1 (8, 17) Iem at t-haplotype transmission TRD level of heterozygotes Rb1+/+t6, Rb1+/+t12, Rb1+/+tw5, Rb1+/+tw18 in crossing with females of different genotypes was studied. Reliable decrease of TRD level in double heterozygotes of Rb1 and haplotypes t12, tw5, tw18 in comparison with the males ++/+t was discovered. For haplotype t6 no differences in TRD between Rb1+/+t6 and ++/+t6 were recorded. The cause of the obtained results is discussed.
The electron microscopic analysis of synaptonemal complexes of the Robertsonian translocation heterozygotes (Rb/T) and heterozygotes of the reciprocal translocation (Rb(8, 17)/T(16, 17) 43H revealed three types of translocation configurations (TC). The observed TC were subdivided into three types according to the manner of synapsis: 1) full synapsis of homologues forming trivalent with interstitial centromere in 15%; 2) the centromeric asynapsis (8 and 17-16 chromosomes forming trivalent with the extension region of asynapsis and breakpoint of the reciprocal translocation on chromosome 17 in 70%; 3) centromeric asynapsis (only single chromosome 17-16 of trivalent, when the break point of reciprocal translocation and the absence of centromeric asynapsis of another chromosome 8 formed trivalent in 15%). The frequency of association between trivalents and the XY bivalents is 20% and close proximity is 15% for heterozygotes Rb/T. Which are fertile, while in the sterile heterozygotes Rb(8, 17)/T(16, 17) 43H it is 45% for association and 15% close proximity (total 60%). These data show the significant differences in the contact of translocation configurations with the XY bivalents of fertile heterozygotes, in comparison with the sterile. Thus, it is shown that the chromosome pairing of fertile and sterile mice is clearly distinguished.
The ability of two inactivated bacterial vaccines, from Proteus vulgaris and Klebsiella pneumoniae, to injure synaptonemal complexes (SCs) was studied by means of electron microscopy. The preparations were given intraperitoneally to C57BL/6J male mice during five successive days and testes were fixed 24 h after the last injection. Cyclophosphamide was used for positive control. The vaccine from Klebsiella given at subtoxic dose, which was about 200 times higher that that given to people during vaccinations, induced the 10-fold rise in the frequency of SC abnormalities in murine 1-storger spermatocytes. Breaks of SCs and of single lateral elements of SCs predominated over other types of vaccine-induced anomalies. According to the preliminary data, vaccine from Proteus at subtoxic dose showed no damaging SC activity. The results of the given study are discussed in connection with the negative data obtained earlier when genotoxicity of these two vaccines had been studied in the Ames test, in routine investigations of bone marrow metaphases of vaccinated mice as well as under light microscopy of their SCs.
The results of genetic analysis of the effects of four novel partial mouse TM-haplotypes are presented in this work. Fertility and viability of tM/tM homozygotes and tM/t6 compounds, transmission ratio distortion (trd) in males heterozygous for tM, suppression of recombination and taillessness effects were studied. Three novel t-haplotypes tM1,2,4 are viable and heterozygous for these haplotypes males T/tM show low trd (20-30%). Comparison of these data and the t6-haplotype structure suggests that the tM1,2,4-haplotypes were derived as a result of recombination events in the non-inverted T-complex fragment located between two inversions. The tM3-haplotype is semilethal and heterozygous T/tM3 males show the trd equal to that of t6-heterozygotes. Homozygous tM3/tM3 and tM3/t6 male compounds are fertile or subfertile. Potential recombination ways of derivation of tM3 are discussed.
Complementation for viability of the compounds tx/ty in complete lethal haplotypes t6, t12, tw5, tw12, tw18, tw73, twPa-1 belonging to the seven basic complementation groups was studied. In the overwhelming majority of crosses a lack of tx/ty offspring was revealed but there is also evidence of non-complete complementation of the tx/ty haplotypes, except for T/tw73XT/tw12, T/tw18XT/t12, T/tw73XT/tw18 crosses in which the level of complementation for viability exceeds 100%. The maternal effect for compound variability was significantly revealed in 9 out of the 19 matings. In addition, reciprocal matings of heterozygotes T/txXT/ty were tested for fertility. In two cases, the maternal effect was also revealed for this character. Comparison of data on viability of the compounds and the fertility of the original strains gives grounds to believe that the tx/ty haplotypes are not completely recessive and partially manifest themselves in the heterozygotes, decreasing fertility in a number of matings. In some cases, these t-haplotypes yield an effect, close to negative complementation, which may be associated with the interaction of the proteins of t-haplotypes.
Fertility of 47 mouse males carrying various combinations of lethal, t-haplotypes (t6/tw18, t12/tw18, Tw73/tw12, tw5/tw18, t6/dt5, t12/tw12, tw5/twPa-1, tw18/twPa-1, tw5/tw12) was studied in crosses with females of different genotypes. The t-haplotypes studied belong to 7 main groups of complementation. The presence of at least two factors of fertility in the t-complex was revealed. The influence of female genotype on the degree of male fertility was also demonstrated. The data presented confirm that different combinations of lethal complete t-haplotypes exhibit sterility, with the exception of t8/tw18 compound.
The mitotic and meiotic chromosomes of four male East-Asiatic mice, Apodemus peninsulae, having three to seven chromosomes in addition to the standard karyotype (2n = 48), were investigated. B-chromosomes were represented by medium-sized metacentric and dotlike chromosomes. Mosaicism of bone marrow cells due to a numerical variation of accessory chromosomes was established for the males examined. Capacity of B-chromosomes to form axial elements and synaptonemal complexes in meiotic prophase I was revealed by electron microscopy. The occurrence of univalents of different morphology, bivalents, and multivalents, corresponding to B-chromosomes, was demonstrated. An increase in the number of B-chromosomes was found in spermatocytes at zygotene-pachytene relative to the number in bone marrow cells, which may be evidence of B-chromosome accumulation in the germ cell line of the East-Asiatic mouse.
Electron microscopic study of total preparations of synaptonemal complexes of spermatocytes I from sterile heterozygous male mice--t12/tw18; tw5/twPa-1; twPa-1/tw18 was performed. T/tw18 and C3H/N fertile heterozygotes were used in each variant as control. The cells are karyotyped in all experiments, as based on the measurements of the length of 19 SC autosomes and SC sex complex. All sterile compounds (spermatocytes) demonstrate high frequency of different types of associations (72%) between sex chromosomes and the autosome 17 carrying a chromosomal aberration in the region of the T-locus. The heterozygotes tx/ty used in our experiments show no disruption of chromosome synapsis, when even studied under electron microscope, though some atypical changes in the ultrastructure of chromosome axes and frequent atypical associations of the axes of XY-sex bivalents in sterile heterozygous animals exist.
The cytogenetic study performed has shown that karyotyping of meiotic cells can be based on the synaptonemal complexes (SC) of spreading pachytene spermatocytes of bull and of horse. The horse SC karyotype has not been previously described. A comparison of the relative length of SC with metaphase chromosomes of bull and horse somatic cells has revealed the correspondence of the chromosome length in pachytene of meiosis and metaphase, which is in agreement with the data on house mouse and Chinese hamster. The method of spreading pachytene cells may be of great practical importance in studies of the fertility disturbances in farm animals.