Nucleolar organizer regions (NORs) distribution and behavior in spermatozoa and meiotic cells of the horse (Equus caballus)

Horse Clinical Cytogenetics: Recurrent Themes and Novel Findings

Clinical cytogenetic studies in horses have been ongoing for over half a century and clearly demonstrate that chromosomal disorders are among the most common non-infectious causes of decreased fertility, infertility, and congenital defects. Large-scale cytogenetic surveys show that almost 30% of horses with reproductive or developmental problems have chromosome aberrations, whereas abnormal karyotypes are found in only 2-5% of the general population. Among the many chromosome abnormalities reported in the horse, most are unique or rare. However, all surveys agree that there are two recurrent conditions: X-monosomy and SRY-negative XY male-to-female sex reversal, making up approximately 35% and 11% of all chromosome abnormalities, respectively. The two are signature conditions for the horse and rare or absent in other domestic species. The progress in equine genomics and the development of molecular tools, have qualitatively improved clinical cytogenetics today, allowing for refined characterization of aberrations and understanding the underlying molecular mechanisms. While cutting-edge genomics tools promise further improvements in chromosome analysis, they will not entirely replace traditional cytogenetics, which still is the most straightforward, cost-effective, and fastest approach for the initial evaluation of potential breeding animals and horses with reproductive or developmental disorders.

Severe asynapsis in spermatocytes of interspecific hybrids of the silver fox (Vulpes vulpes) and the blue fox (Alopex lagopus) leads to pachytene I arrest as a result of sustained H2AXγ phosphorylation

Infertility is frequently associated with meiotic anomalies which can result in the production of chromosomally abnormal gametes or be concomitant with meiotic arrest. We investigated whether spermatocytes of male interspecific hybrids of the red fox (Vulpes vulpes) and the arctic fox (Alopex lagopus) presented alterations in chromosomal synapses and meiotic checkpoint signalling. Using the immunofluorescence technique with SP1 and SP3 proteins, bivalent structures and their deviations (multivalents, univalents and not fully conjugated bivalents) were analyzed on meiotic preparations. This technique allowed the localization of frequent foci of phosphorylated histones H2AHγ (Ser 139) to the meiotic block in late pachytene. These results indicate a disruption of meiotic division in male fox hybrids, which leads to a high percentage of apoptotic cells in the gonads of these animals and, consequently, sterility.

The effect of Robertsonian translocations on the intranuclear positioning of NORs (nucleolar organizing regions) in human sperm cells

Only a few studies have described sperm chromosome intranuclear positioning changes in men with reproductive failure and an incorrect somatic karyotype. We studied the influence of Robertsonian translocations on the acrocentric chromosome positioning in human sperm cells. The basis of the analysis was the localization of NORs (nucleolar organizing regions) in sperm nuclei from three Robertsonian translocation carriers, namely, rob(13;22), rob(13;15) and rob(13;14), with a known meiotic segregation pattern. All three carriers presented with a similar percentage of genetically normal sperm cells (i.e., approximately 40%). To visualize NORs, we performed 2D-FISH with directly labelled probes. We used the linear and radial topologies of the nucleus to analyse the NORs distribution. We found an affected positioning of NORs in each case of the Robertsonian translocations. Moreover, the NORs tended to group, most often in two clusters. Both in Robertsonian carriers and control sperm cells, NORs mostly colocalized in the medial areas of the nuclei. In the case of the Roberstonian carriers, NORs were mostly concentrated in the peripheral part of the medial area, in contrast to control sperm cells in which the distribution was more dispersed towards the internal area.