Robertsonian Translocation Rb Research Articles

Unusual congenital polydactyly in mini-pigs from the breeding group of the Institute of Cytology and Genetics (Novosibirsk, Russia).

The article describes a new phenomenon in the breeding group of mini-pigs at the Institute of Cytology and Genetics (ICG, Novosibirsk): polydactyly (extra digits), which is unusual because the additional digits are situated at the lateral surface of legs or at the lateral and medial ones. This anomaly was f irst found here in 2017 in adult animals intended for culling due to incorrect positioning of the legs caused by f lexor tendon laxity and resulting in weight-bearing on the palmar surface of the proximal phalanges (“bear’s paw”). Therefore, the polydactyly of mini-pigs has a pronounced negative selection effect. A visual survey of the livestock was conducted, and a description of the detected anomaly was compiled. The polydactyly in mini-pigs is a stand-alone trait and is not part of any syndromes. Individuals with polydactyly may have extra digits either on pectoral or on pectoral and pelvic limbs. On thoracic limbs, there may be either one lateral digit or a lateral digit and a medially located rudimentary hoof let. On pelvic limbs, only lateral extra digits can occur. Anatomical and morphological analyses showed that the lateral extra digit is an anatomically complete (“mature”) structure, whereas the medial rudimentary digit consists of only a hoof let without other structures characteristic of normal digits. Cytological examination revealed no specif ic karyotypic features, except for Robertsonian translocation Rb 16;17 previously reported for the mini-pigs of the same livestock. Cytological f indings indicated that the polydactyly and Robertsonian translocation are not linked genetically. Genealogical analysis and results of crosses are consistent with a working hypothesis of recessive inheritance of the trait. Overall, the study shows that this type of polydactyly is anatomically and morphologically unique and not typical of Sus scrofa. In this species, only polydactyly types with medial accessory toes have been described and are usually inherited as a dominant trait with incomplete penetrance. In our case, the results of test crosses indicate recessive inheritance of the trait with varying expression and incomplete penetrance, because of which poorly expressed phenotypes are not visually detectable.

Defective imprint resetting in carriers of Robertsonian translocation Rb (8.12)

Meiotic silencing of unsynapsed chromatin (MSUC) occurs in the germ cells of translocation carriers and may cause meiotic arrest and infertility. We hypothesized that if bypassing meiotic checkpoints MSUC may cause epigenetic defects in sperm. We investigated the meiotic behavior of the Robertsonian translocation Rb (8.12) in mice. The unsynapsed 8 and 12 trivalent was associated with the XY body during early and mid-pachynema in heterozygous Rb (8.12) carriers, suggesting possible silencing of pericentromeric genes, such as the Dnmt3a gene. In wild-type mice, DNMT3A protein showed a dramatic accumulation in the nucleus during the mid-pachytene stage and distinct association with the XY body. In translocation carriers, DNMT3A was less abundant in a proportion of pachytene spermatocytes that also had unsynapsed pericentromeric regions of chromosomes 8 and 12. The same mice had incomplete methylation of the imprinted H19 differentially methylated region (DMR) in sperm. We propose that impaired H19 imprint establishment results from lack of synapsis in chromosomes 8 and 12 probably through transient silencing of a chromosome 8 or 12 gene during pachynema. Furthermore, our findings support the notion that imprint establishment at the H19 locus extends into pachynema.

A Robertsonian translocation suppresses a somatic recombination pathway to loss of heterozygosity.

In mammals, loss of APC/Apc gatekeeper function initiates intestinal tumorigenesis. Several different mechanisms have been shown or proposed to mediate functional loss of APC/Apc: mutation in APC/Apc, non-disjunction, homologous somatic recombination and epigenetic silencing. The demonstration that, in the C57BL/6 (B6) Apc(Min/+) mouse model of inherited intestinal cancer, loss of Apc function can occur by loss of heterozygosity (LOH) through somatic recombination between homologs presents an opportunity to search for polymorphisms in the homologous somatic recombination pathway. We report that the Robertsonian translocation Rb(7.18)9Lub (Rb9) suppresses the multiplicity of intestinal adenomas in this mouse model. As the copy number of Rb9 increases, the association with the interphase nucleolus of the rDNA repeats centromeric to the Apc locus on Chromosome 18 is increasingly disrupted. Our analysis shows that homologous somatic recombination is the principal pathway for LOH in adenomas in B6 Apc(Min/+) mice. These studies provide additional evidence that neoplastic growth can initiate in the complete absence of canonical genomic instability.

Inhibition of Histone Deacetylases Alters Allelic Chromatin Conformation at the Imprinted U2af1-rs1 Locus in Mouse Embryonic Stem Cells

Most loci that are regulated by genomic imprinting have differentially methylated regions (DMRs). Previously, we showed that the DMRs of the mouse Snrpn and U2af1-rs1 genes have paternal allele-specific patterns of acetylation on histones H3 and H4. To investigate the maintenance of acetylation at these DMRs, we performed chromatin immunoprecipitation on trichostatin-A (TSA)-treated and control cells. In embryonic stem (ES) cells and fibroblasts, brief (6-h) TSA treatment induces global hyperacetylation of H3 and H4. In ES cells only, TSA led to a selective increase in maternal acetylation at U2af1-rs1, at lysine 5 of H4 and at lysine 14 of H3. TSA treatment of ES cells did not affect DNA methylation or expression of U2af1-rs1, but was sufficient to increase DNase I sensitivity along the maternal allele to a level comparable with that of the paternal allele. In fibroblasts, TSA did not alter U2af1-rs1 acetylation, and the parental alleles retained their differential DNase I sensitivity. At Snrpn, no changes in acetylation were observed in the TSA-treated cells. Our data suggest that the mechanisms regulating histone acetylation at DMRs are locus and developmental stage-specific and are distinct from those effecting global levels of acetylation. Furthermore, it seems that the allelic U2af1-rs1 acetylation determines DNase I sensitivity/chromatin conformation.

Genetic aspects of animal reasoning

This paper reviews the investigations of Prof. L. V. Krushinsky and his colleagues into the genetics of complex behaviors in mammals. The ability of animals to extrapolate the direction of a food stimulus movement was investigated in wild and domesticated foxes (including different fur-color mutants), wild brown rats, and laboratory rats and mice. Wild animals (raised in the laboratory) were shown to be superior to their respective domesticated forms on performance of the extrapolation task, especially in their scores for the first presentation, in which no previous experience could be used. Laboratory rats and mice demonstrated a low level of extrapolation performance. This means that only a few laboratory animals were capable of solving the task, i.e., the percentage of correct solutions was equivalent to chance. The brain weight selection program resulted in two mice strains with a 20% (90-mg) difference in brain weight. Ability to solve the extrapolation task was present in low-brain weight mice in generations 7-11 but declined with further selection. Investigation of extrapolation ability in mice with different chromosomal anomalies demonstrated that animals with Robertsonian translocations Rb(8,17) 1lem and Rb(8,17) 6Sic were capable of solving this task in a statistically significant majority of cases, while mice with fusion of other chromosomes, as well as CBA normal karyotype mice, performed no better than expected by chance. Mice with two types of partial trisomies and animals homo- and heterozygous for translocations were also tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Assignment of the gene coding for the α2-macroglobulin receptor to mouse chromosome 15 and to human chromosome 12q13–q14 by isotopic and nonisotopic in situ hybridization

The assignment of the gene encoding the α 2-macroglobulin receptor (A2MR), which was first described as the low-density lipoprotein receptor-related protein, was confirmed by nonisotopic and isotopic in situ hybridizations on normal human metaphases to the region 12q13–q14. The same human cDNA, which has 95% sequence identity with the mouse A2mr, was hybridized to metaphases containing the Robertsonian translocation Rb(6;15) 1Ald. The mouse A2mr gene was assigned to chromosome 15 in the region B2-D1. this locus and other loci on mouse chromosome 15 have been shown to be homologous with loci on human chromosome 12q.

Meiotic drive of t haplotypes: chromosome segregation in mice with tertiary trisomy

The properties of the t haplotypes, specific mutant states of the proximal region of chromosomes 17 in the house mouse, are of continuing interest. One such property is increased transmission of the t haplotype by heterozygous t/+ males to offspring. Using the reciprocal translocation T(16;17)43H we have constructed males with tertiary trisomy of chromosome 17 (+T43/+ +/Rb7+) carrying the Robertsonian translocation Rb(16.17)7Bnr. Only the progeny of these males which had inherited either T43/+ or Rb7 from their male parent were viable. The segregation patterns in the offspring of t-bearing trisomics were analysed on days 16-18 of embryonic development. It was found that, when the t12 haplotype is in the normal acrocentric (males+ +T43/+ t12 + /Rb7+ +), its presence in the gamete +t12+/+ + T43 does not produce meiotic drive. However, when t6 is in Rb7, meiotic drive was observed: 80% of offspring carried the t haplotype. It is concluded that the meiotic drive is probably inhibited by the presence of a normal homologue of chromosome 17 in the same sperm. Possible mechanisms for the t haplotype effect are discussed.

Analysis of recombination in the centromere region of mouse chromosome 7 using ovarian teratoma and backcross methods.

Recombination near the centromere of mouse chromosome 7 was studied using data obtained from ovarian teratomas and backcrosses. The recombination percentage for the centromere-Gpi-1 (glucose phosphate isomerase-1) interval was 13.4 +/- 2.6 using the ovarian teratoma mapping method. In a backcross using the Robertsonian translocation Rb(7.18)9Lub (Rb9) as the centromeric marker, the centromere-Gpi-1 recombination percentage was 4.5 +/- 1.3, demonstrating that Rb9 suppresses recombination near the centromere of chromosome 7. The recombination percentage for the Gpi-1-Ldh-1 (lactate dehydrogenase-1) interval was estimated on the LT/Sv mouse genetic background to be 19.0 +/- 2.9 using the ovarian teratoma mapping method, a value comparable to the 15.5 +/- 4.8 reported earlier. On the same genetic background in a backcross segregating for Rb9, the Gpi-1-Ldh-1 recombination percentage was 7.1 +/- 1.6. Another backcross, without the Rb9 translocation but utilizing a different genetic background, produced a recombination percentage for the Gpi-1-Ldh-1 interval of 10.7 +/- 1.5, a value similar to that obtained in the Rb-containing cross. These results suggest that either the recombination suppression in the centromere area caused by Rb9 does not extend to the Gpi-1-Ldh-1 genetic region or, if it does, that the differing genetic backgrounds of these two crosses influence recombination. No recombinants were detected among 410 offspring produced from a backcross mating segregating for Ldh-1 and ru-2 (ruby-eye-2). Thus, the gene order of Ldh-1 and ru-2 on chromosome 7 remains uncertain.

The influence of mutations on chromosome 17 upon the segregation of homologues in female mice heterozygous for Robertsonian translocations.

SummaryThe influence of mutations in chromosome 17 upon the segregation of the metacentric and acrocentric homologues in the progeny of female mice heterozygous for Robertsonian translocations Rb(8.17)11em and Rb(16.17)7Bnr was studied. Genetic analysis indicated that the portion of non-Rb (normal karyotype) progeny from mothers heterozygous for mutations tf, qk, t12 was weakly different from the 50% Mendelian expected level (55–57%). Introduction of mutations T, FuKi, Fu, t6 into the female genotype caused a stronger segregation distortion and an increase in the portion of progeny with normal karyotype (63–67%). From the data on embryonic mortality and cytogenetic observations it is concluded that a distortion of equal transmission arises before M II of meiosis. Consequently, the preferential distribution of the metacentric chromosome to the polar body during the first meiotic division is relevant to the observed segregation distortion.

Stereomicroangiography in embryologic and teratologic investigation.

Vascular dysmorphogenesis is usually investigated by invasive microdissection or time-consuming reconstruction of serial sections. Stereomicroangiography (SMA) was used for detection and analysis of vascular abnormalities in a murine trisomy 13 model demonstrating pulmonary atresia. Twenty-two litters from doubly heterozygous Robertsonian translocation Rb(6.13)3Rma/Rb(5.13)70Lub male matings to NMRI females were studied. Embryos (13-17 days gestation) were prepared by umbilical vein perfusion with buffered fixative and umbilical artery perfusion with 5% AgNO3. After immersion fixation specimens were infiltrated with paraffin, mounted on stubs, and stereoradiographed at multiple angles. Transverse serial sections were prepared of the thoracic area. Thoracic vascular morphology was satisfactorily imaged and trisomy 13 embryos were correctly distinguished from normals in 105 of 120 embryos (87.5%). When independent SMA and histologic interpretations were compared anomalous vasculature was correctly identified in all 27 trisomic embryos and one control, and falsely interpreted in one normal embryo. Normal vascular morphology was demonstrated in the remaining 76 normal embryos. Separate SEM evaluation of five microdissected hearts from nontrisomic embryos following this perfusion schedule showed normal distension of the ventricular cavity and metallic silver deposition on the surface and at junctions of endocardial cells. Light microscopy revealed silver staining at the endothelial surface and within the endocardial cushions. SMA accurately records embryonic vascular morphology for rapid screening of viable embryos.

Cloning of DNA libraries from mouse Y chromosomes purified by flow cytometry

To purify mouse Y chromosomes by flow cytometry, a male cell line containing the Robertsonian translocation Rb(9.19)163H has been established by SV40 transformation. Flow karyotypes obtained from these cells exhibit a well-isolated peak of fluorescence corresponding to the single Y chromosome, clearly distinct from that of chromosome 19. From this peak, 650,000 chromosomes were sorted, and two restriction fragment libraries were constructed from the DNA of the sorted chromosomes. The characterization of several Y-specific fragments has shown that the Y DNA was enriched at least 36-fold. Furthermore, given that there are likely homologies between the X and Y chromosomes, we can assume that this calculated value of the purification factor is an underestimation and that the Y DNA was more highly purified by flow sorting.

Location of plucked (pk) on chromosome 18 of the mouse.

Plucked (pk), a recessive hair-type mutation in the mouse, has been assigned to chromosome 18 at a location between Tw and syfp. The Robertsonian translocation Rb(7.18)9Lub was found to suppress crossing over in the proximal half of this chromosome.

Genes on chromosome 3 of the mouse.

We have located three loci on Chromosome 3 : carbonic anhydrase-1 (Car-1), carbonic anhydrase-2 (Car-2), and blebs (my). The Robertsonian translocation Rb(1.3) 1Bnr was used as a marker for the centromere of Chromosome 3. The loci map is as follows: centromere-2.5cM-(Car-1, Car-2)-26cM-my.

A genetic method for measuring non-disjunction in mice with Robertsonian translocations.

SUMMARYA high frequency of chromosomal non-disjunction occurs spontaneously in mice heterozygous for some Robertsonian translocations. If animals heterozygous for the translocation and homozygous for different alleles of a marker gene are mated together a few young homozygous for the marker arise through non-disjunction, and their frequency can be used as a measure. This method has been used with the Robertsonian translocation Rb(9.19)163H and the marker ruby ru (chr. 19); Rb(4.6)-2Bnr with brown (b) and misty (m) (chr. 4); and Rb(9.14)6Bnr with hairless (hr) and piebald (s) (chr. 14) respectively. The frequencies of marked young were: Rb163 0/5260 ruru; Rb2 21/1997 mm bb; and Rb6 19/1702 hrhr ss, and the corresponding calculated non-disjunction frequencies in each arm of the translocation were Rb163, <5 %; Rb2, 15%; Rb6, 15%. These figures show reasonably good agreement with values obtained by other methods. A search for genetic or environmental factors affecting the frequency of marked young in Rb2 and Rb6 revealed that in Rb2 the frequency increased with maternal age, whereas in Rb6 the maternal age of the marked young was non-significantly below that of the total progeny. The reasons for this discrepancy are not clear.