A potential relationship between the 16;20 and 14;20 Robertsonian translocations and low in vitro embryo development

Sperm chromosome segregation of rob(4;16) and rob(4;16)inv(4) in the brown brocket deer (Mazama gouazoubira)

The genus Mazama stands out among the Neotropical deer due to their wide intra and interspecific karyotypic diversification, which is associated with an accentuated chromosomal fragility. There are reports of heterozygous Robertsonian translocation (RT) carriers in a free-range population of Mazama gouazoubira (brown brocket deer), as well as in captive animals of this and other species of the genus. To analyze possible negative impacts of heterozygous chromosome rearrangements on reproductive fitness of the carriers, we performed an analysis of sperm meiotic segregation in four brown brocket bucks, carriers of a rob(4;16), and compared the results with those of a normal buck. We established a reliable FISH and sperm-FISH protocol for the brown brocket deer using bovine (Bos taurus; diploid number, 2n = 60) whole chromosome painting (WCP) and BAC probes. Using BAC probes, we revealed the presence of a paracentric inversion (PAI) of the fused chromosome 4 in two of the four analyzed RT carriers. The mean frequency of normal/balanced sperm in the translocation carriers was significantly lower than in the normal buck (94.78% vs 98.40%). The mean value of total unbalanced spermatozoa was almost doubled in the RT/PAI carriers (6.68%) when compared to RT carriers (3.76%), but the difference was not statistically significant. This study demonstrated the efficiency of FISH with bovine WCP and BAC probes in the characterization of chromosome rearrangements and gametic segregation patterns in brown brocket deer. Our results indicate a low to moderate increase in the rates of unbalanced meiotic segregation products in brown brocket bucks heterozygous for RT and RT/PAIs.

Chromosome Abnormalities and Fertility in Domestic Bovids: A Review

Simple Summary

In domestic bovids, numerical autosome abnormalities have been rarely reported, as they present abnormal animal phenotypes quickly eliminated by breeders. However, numerical abnormalities involving sex chromosomes and structural (balanced) chromosome anomalies have been more frequently detected because they are most often not phenotypically visible to breeders. For this reason, these chromosome abnormalities, without a cytogenetic control, escape animal selection, with subsequent deleterious effects on fertility, especially in female carriers.

Abstract

After discovering the Robertsonian translocation rob(1;29) in Swedish red cattle and demonstrating its harmful effect on fertility, the cytogenetics applied to domestic animals have been widely expanded in many laboratories in order to find relationships between chromosome abnormalities and their phenotypic effects on animal production. Numerical abnormalities involving autosomes have been rarely reported, as they present abnormal animal phenotypes quickly eliminated by breeders. In contrast, numerical sex chromosome abnormalities and structural chromosome anomalies have been more frequently detected in domestic bovids because they are often not phenotypically visible to breeders. For this reason, these chromosome abnormalities, without a cytogenetic control, escape selection, with subsequent harmful effects on fertility, especially in female carriers. Chromosome abnormalities can also be easily spread through the offspring, especially when using artificial insemination. The advent of chromosome banding and FISH-mapping techniques with specific molecular markers (or chromosome-painting probes) has led to the development of powerful tools for cytogeneticists in their daily work. With these tools, they can identify the chromosomes involved in abnormalities, even when the banding pattern resolution is low (as has been the case in many published papers, especially in the past). Indeed, clinical cytogenetics remains an essential step in the genetic improvement of livestock.

Influence of sperm fertilising concentration, sperm selection method and sperm capacitation procedure on the incidence of numerical chromosomal abnormalities in IVF early bovine embryos

The occurrence of numerical chromosomal aberrations, widely described as a major cause of mortality in in vitro-produced (IVP) embryos, has been linked to several factors. In the present study we investigated the effect of sperm fertilising concentration and semen handling (sperm selection and capacitation) before IVF on the rate of numerical chromosomal abnormalities in bovine embryos. In all, 466 IVP cattle embryos were karyotyped throughout three sequential experiments, analysing the effects of sperm fertilising concentration (0.1, 1.0 or 10×10(6) spermatozoa mL(-1)), selection method (unselected or Percoll-selected spermatozoa) and capacitation medium (bovine serum albumin (BSA), heparin or their combination). The percentage of normal (diploid) and aberrant (haploid, polyploid or aneuploid) embryos was noted in each experiment. The rate of numerical chromosomal abnormalities was mainly affected by sperm fertilising concentration (P<0.01) and, to a lesser extent, by the sperm capacitation medium (P<0.05). Polyploidy and haploidy rates were only affected by sperm fertilising concentration (P<0.05). Interestingly, the sperm selection technique used in the present study did not reduce the incidence of chromosome abnormalities in IVP cattle embryos (P>0.05). Finally, aneuploidy rates were not affected during the experiments (P>0.05), which suggests that they are not related to sperm-related factors. On the basis of these results, we conclude that sperm fertilising concentration is the 'paternal' key factor that affects the rate of numerical chromosomal abnormalities in IVP bovine embryos. By making small adjustments to fertilising protocols, the rate of cytogenetically aberrant embryos can be markedly reduced.

Robertsonian translocation as a result of telomere shortening during replicative senescence and immortalization of bovine oviduct epithelial cells

We investigated chromosome (Chr) aberrations in the process of replicative senescence and immortalization of cultured bovine oviduct epithelial cells (BOEC) before and after transfecting vectors SV40 large T or human telomerase reverse transcriptase (hTERT). We found that a gradual increase in the number of metacentric chromosomes occurred during replicative senescence but not immortalization of BOEC. The accumulation of metacentric chromosomes was concomitant with decreases in the number of acrocentric autosomes, strongly suggesting that Robertsonian (Rb) translocation frequently occurred in cultured BOEC. The process was also correlated with an accumulation of extremely shortened telomeres (<4 kb). The maximum number of metacentric chromosomes reached a plateau (8.75 +/- 0.53) in the senescent BOEC (approximately 48 population doublings), and the value was stably maintained in all immortalized lines. These results suggest that not all autosomes may be involved in Rb translocation. Fluorescence in situ hybridization analysis using probes specific for Chr1, Chr29, telomeres, and x-chromosomes of bovine confirmed the presence of t(1;29) with other unidentified fused chromosomes. There was no evidence for duplication of sex chromosomes. Because no detectable fluorescence in situ hybridization signals at the centromere for telomeres were indicative of no direct integration of telomere sequences in the Rb translocated chromosomes, these results raise a possibility that Rb translocation between certain autosomes of bovine cells is partly but critically dependent upon a physical state of telomere attrition. The cells and cell lines established in this study could provide a promising system for further studies on the mechanisms of chromosomal translocation because of centromeric fusion in bovine cells.

New Robertsonian translocation chromosomes in captive Thai gaur (Bos gaurus readei)

Robertsonian translocation have been well documented in domestic cattle, with the most commonly occurring fusion involving chromosomes 1 and 29. The widespread nature of this translocation is indicative of its ancient origin. Fifty Giemsa's stained metaphase spreads derived from lymphocyte cultures of the Thai gaur were analyzed for each animal. The Thai gaur had diploid chromosome number of 2n = 57 in male and 2n = 56 in female instead of the normal 2n = 58. The 2n = 57 in male chromosomes presence of an extra submetacentric chromosome and loss of two acrocentric chromosomes was observed [XY, 57, rob (1;29)]. The 2n = 56 in female chromosomes presence of two extra submetacentric chromosomes and loss of four acrocentric chromosomes was observed [XX, 56, rob (1;29)]. Results from the Giemsa's stained analyses confirm that the two autosomes (2n = 57) and four autosomes (2n = 56) involved in the translocation are the bovine homologues 1 and 29.

Differential susceptibility to chromatid breaks induced by bleomycin in sub-fertile and fertile bovines

The rate of chromatid breaks was studied in cows with a history of sub-fertility by means of a test based on measurement of the average of breaks induced in lymphocytes of peripheral blood cultures. Fourteen female specimens were divided into two groups: fertile and sub-fertile. Peripheral blood lymphocytes were cultured and prepared for cytogenetic analysis. Two types of culture were established for each animal to evaluate the response of peripheral blood lymphocyte cultures to the genotoxic effects of bleomycin. The first culture did not receive bleomycin treatment (spontaneous chromosome aberrations). Our results showed that median breaks per cell (b/c) (+/-semirange) for spontaneous culture of the fertile and sub-fertile animals and bleomycin sensitivity assay for fertile and sub-fertile animals were 0.00+/-0.06, 0.02+/-0.03, 0.08+/-0.05 and 0.22+/-0.09, respectively. There was no significant difference (P>0.05) in the chromosomal breakage in lymphocytes not exposed to bleomycin; however, in comparing the number of chromatid breaks per cell in cultures treated with bleomycin, the sub-fertile group showed a significantly higher (P<0.05) level than the fertile group. These findings have implications both for identifying cattle with less than optimum fertility as well as for providing potential avenues to study the origins of sub-fertility.