L. D. Safronova

The Ecology and Evolutionary Dynamics of Meiotic Drive

Meiotic drivers are genetic variants that selfishly manipulate the production of gametes to increase their own rate of transmission, often to the detriment of the rest of the genome and the individual that carries them. This genomic conflict potentially occurs whenever a diploid organism produces a haploid stage, and can have profound evolutionary impacts on gametogenesis, fertility, individual behaviour, mating system, population survival, and reproductive isolation. Multiple research teams are developing artificial drive systems for pest control, utilising the transmission advantage of drive to alter or exterminate target species. Here, we review current knowledge of how natural drive systems function, how drivers spread through natural populations, and the factors that limit their invasion.

Meiotic drive in mice carrying t-complex in their genome

The deviation of alleles and chromosomes from Mendelian inheritance is characteristic of the meiotic drive. This review describes the mechanism in question using the best-studied example of transmitted ratio distortion in the heterozygous male mice carrying t-haplotypes. The t-complex is best model for studying the meiotic drive under laboratory conditions. Putative mechanisms of meiotic drive that influence the frequency of t-haplotypes in natural populations are considered, of which prezygotic selection is the most important. The role of meiotic drive in male hybrid sterility is emphasized. The factors and models that determine the phenomenon of meiotic drive are discussed in detail.

Influence of Cats’ Urinary Chemosignals on Sexual Maturation and Meiosis in Campbell’s Hamster Males (Phodopus Campbelli)

This study was conducted to reveal a possible influence of cat urine on reproductive development in male Campbell’s hamsters (Phodopus campbelli). In Experiment 1, males were treated every other day with cat urine or water (control) from Day 11 (Dl1). At D30 body and epididymis weights were significantly reduced but relative adrenal gland weight was higher in cat urine treated juveniles. These data suggest that the suppressive influence of cat urine on reproductive development involves the adrenal-pituitary axis and cat urine could be considered a stress factor. Experiment 2 was done to check whether decreases in epididymis weight correspond with meiotic disturbance in prepubertal hamster males. Males were exposed to cat urine or water from D15 until D45. At D45 males were unilaterally gonadectomized and electronmicroscopic analysis of spread spermatocyte preparations was performed. The analysis of synaptonemal complexes (SC) of pachytene nuclei revealed no abnormalities in either sex chromosomes or autosomes in control hamsters. However, in the cat urine treated group, abnormal SC configurations that included partial autosomal asynapsis combined with interlocking and sex chromosome dissociation were found. These data indicate that the disturbance of homologous synapsis at the first meiotic prophase may at least in part explain the decrease of epididymis weight in cat urine treated hamsters.

Stability of the population variants of the B-chromosome system in the East-Asian mouse Apodemus peninsulae from the Baikal region and Northern Mongolia

Analysis of the B-chromosome frequency and morphotypes in 160 mice Apodemus peninsulae from 17 localities of the Baikal region, Northern Mongolia, Trans-Baikalia, and the Russian Far East showed that the mice were from five geographical populations. The interpopulation difference was determined by variations of 0–4 macro B chromosomes and 0–11 micro B chromosomes. The B-chromosome number and morphotypes proved to be stable over the past 30 years in the geographical populations under study.

Meiosis in gray voles of the subgenus Microtus (Rodentia, Arvicolinae) and in their hybrids

The results of light and electron microscopic (EM) studies of meiosis in Microtus arvalis males of the karyoform “arvalis” (2n = 46, NFa = 80), in hybrids between the chromosomal forms arvalis and obscurus (2n = 46, NFa = 68), in M. rossiaemeridionalis voles (2n = 54, NFa = 54), and in a hybrid between the species M. rossiaemeridionalis and kermanensis (2n = 54, NFa = 54) are presented. SC (synaptonemal complex) karyotypes of the parental forms and the hybrids were constructed on the basis of measurements of the length of autosomal SCs revealed by the EM analysis in spermatocytes at the stage of middle pachytene. The SC karyotypes of M. arvalis and the hybrids ♀ obscurus × ♂ arvalis consist of 22 synaptonemal complexes of autosomal bivalents and the axial elements of the synaptonemal complexes of the sex chromosomes X and Y. The SC karyotypes of M. rossiaemeridionalis and the hybrid M. rossiaemeridionalis × M. kermanensis consist of 26 synaptonemal complexes of autosomal bivalents and a sex bivalent; they differ only in the length of the Y chromosome axis (Y chromosome in the hybrid was inherited from M. kermanensis). Asynaptic configurations of the autosomal SCs were not observed in the hybrids. The SC axial elements of the X and Y chromosomes in the parental forms and in the hybrids were located close to each other throughout pachytene, but they did not form a synaptic region. The normal synapsis in sterile hybrids (M. rossiaemeridionalis × M. kermanensis) and the behavior of the sex chromosomes in meiosis in fertile and sterile hybrids are discussed in the context of specific features of meiosis and reproductive isolation.

The expression of transmission ratio distortion (TRD) and the frequency of carriers of t haplotypes in natural populations of house mice Mus musculus.

The character of TRD (transmission ratio distortion) was analyzed using the database formed on the basis of the results obtained for a collection of mice carrying different t haplotypes during 30 years of experimental observations. Quantitative TRD parameters were determined in male mice with T/tw genotypes from natural populations in crosses with females from laboratory collections. The TRD value varied in the range from 0.41 to 0.74. The frequencies of t haplotypes in natural Mus musculus populations from different regions (Moscow, Moscow oblast, Tajikistan, Lithuania, and Mongolia) varied from 12% (Tigrovaya Balka, Tajikistan) to 44% (Ulan-Bator, Mongolia). The factors and mechanisms determining a low frequency of t haplotypes in natural populations are discussed.

Synaptonemal Complex of Two Fish Species of the genus Nothobranchius (Cyprinodontidae)

The karyotype of males of two species of the genus Nothobranchius with the lowest diploid numbers was investigated: Nothobranchius rachovi (2N = 16) and Nothobranchius krysanovi (2N = 18). For the first time, whole mounts of spread syneptonemal complexes (SC) of these species were obtained and investigated. When the SC was painted with silver nitrate and immunostained with rabbit antibodies against the SCP3 protein, eight and nine homomorphic SCs were detected in the nuclei of class I spermatocytes of N. krysanovi and N. rachovi, respectively. The sex chromosomes were not identified.

Evaluation of Phylogenetic Relationships in the Genus Mus Using t -Specific Microsatellite DNA Markers

The t-complex includes a complex system of genes localized in the proximal region of chromosome 17 of house mouse Mus musculus. The results of microsatellite analysis of laboratory stocks of house mice carrying t12, tw5, tw12, and tw73 haplotypes and wild mice from natural populations of Russia (Volgograd, Rostov, Saratov oblasts, and Kalmykia), Armenia, Bulgaria, Iran, and Mongolia performed by the PCR method with the use of eight pairs of D17Mit primers (16, 21, 23, 28, 32, 57, 63, 78) are presented. These pairs of primers amplify microsatellite DNA sequences on mouse chromosome 17 in the region from 7.6 to 18.8 cM that correspond to inversions (In (17) 3.4). Each pair of primers recognized three to six variants of nucleotide sequences ranging in size from 90–120 bp (D17Mit 16) to 300–330 bp (D17Mit 57). In most cases, two variants of nucleotide sequences were detected in each individual, i. e., most individuals were heterozygous for the microsatellite loci under study. The highest similarity of the spectra of microsatellite DNA fragments was revealed in laboratory stocks of house mice carrying the tw5 and tw73 haplotypes. The spectra of animals from the Rostov and Volgograd oblasts appeard to be most similar to them. The microsatellite spectra of individuals from Iran closely resemble the spectrum of an individual from Armenia. It was demonstrated that amplified microsatellite fragments localized in the region of the t-complex can be used to identify representatives of the Mus genus from wild populations.

Behavior of sex chromosomes at early meiosis stages in three wood mice species of the genus Apodemus (Rodentia, Muridae)

The prophase of the first meiotic division was studied in field mice of the species Apodemus (Sylvaemus) flavicollis, A. (S.) ponticus, and A. (S.) uralensis by light and electron microscopy. The karyotypes of three species were described on the base of electron microscopy of synaptonemal complexes in spermatocytes I. The axial elements of the sex chromosomes at early-middle pachytene synapse along the major portion of the Y axis; at late pachytene-early diplotene, the synapsis region shrinks; and at diakinesis-metaphase I, X and Y chromosomes associate end-to-end in all species studied. The behavior of sex chromosomes in the synapsis in the species studied was quite uniform. The results are discussed in the context of earlier data on the behavior of sex chromosomes in various rodent species in meiosis prophase I and their banding.

Transmission Ratio Distortion, Sterility, and Control of the t-Complex Function in Sperm

Mouse t-complex located on chromosome 17 contains genes affecting only 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.