Chromosomal expression and localization of aphidicolin-induced fragile sites in the standard karyotype of river buffalo <i>(Bubalus bubalis)</i>

Abstract

The present study reports on the chromosomal expression and localization of aphidicolin-induced fragile sites in the standard karyotype of river buffalo (Bubalus bubalis, 2n = 50) with the aim of establishing a ‘fragile site map’ of the species. Totally, 400 aphidicolin-induced breakages were analyzed from eight young and clinically healthy animals, four males and four females; these breakages were localized in 106 RBG-negative chromosome bands or at the band-interband regions. The number of breakages per chromosome did not vary statistically ‘among’ the animals investigated but the differences among individual chromosomes were highly significant thus indicating that the chromosomal distribution of the breakages is not random and appears only partially related to chromosome length. Fragile sites were statistically determined as those chromosomal bands showing three or more breakages. In the river buffalo karyotype, 51 fragile sites were detected and localized on the standardized ideogram of the species. The most fragile bands were as follows: 9q213 with 24 breakages out of 400; 19q21 with 16, 17q21 and inacXq24 with 15, 15q23 with 13 and 13q23 with 12 breaks, respectively. Previous gene mapping analysis in this species has revealed that the closest loci to these fragile sites contain genes such as RASA1 and CAST (9q214), NPR3 and C9 (19q19), PLP and BTK (Xq24-q25), OarCP09 (15q24), and EDNRB (13q22) whose mutations are responsible for severe phenotypic malformations and immunodeficiency in humans as well as in mice and meat quality in pigs. Further cytogenetic and molecular studies are needed to fully exploit the biological significance of the fragile sites in karyotype evolution of domestic animals and their relationships with productive and reproductive efficiency of livestock.

Comparative Mapping and Genomic Annotation of the Bovine Oncosuppressor Gene <i>WWOX</i>

“…There is great interest in fragile sites, as they show a nonlinear distribution throughout genomes and frequently overlap the so-called evolutionary breakpoints Ruiz-Herrera et al, 2006]. The localization of the WWOX gene obtained in this study is in good agreement with breakpoints induced by aphidicolin treatment for Bos taurus , specifically at BTA18q12 [Rodrigues et al, 2002], and to a minor extent with the data reported in a similar study on Bubalus bubalis where the closest aphidicolin-induced fragile site is mapped to BBU18q21 [Nicodemo et al, 2008]. However, it should be pointed out that the conservation of fragile sites seems more significant than that suggested by cytogenetic approaches, as clearly shown by studies that extended the comparison between mouse and man to other speciesincluding domestic animals and cattle -and exploited genome assemblies as an additional and more powerful tool for analysis [Murphy et al, 2005].…”

“…In domestic animals fragile sites have not received much attention, although published data suggest the importance of developing species-specific genome maps for fragile sites as a tool for studies of karyotype evolution, comparative genomics and mutational cytogenetics [Rodriguez et al, 2002;Nicodemo et al, 2008]. We have focused our attention on the isolation and annotation in the bovine genome of genes known to map at common fragile sites exploiting their high conservation and using a comparative approach.…”

Fragile Sites in Domestic Animal Chromosomes: Molecular Insights and Challenges

“…Fragile sites have been identified in the river buffalo karyotype ( Bubalus bubalis) . The most recent efforts were described in conjunction with high resolution karyotype s [Pires et al, 1998;Mahrous and Ahmed, 2000;Sanghamitra et al, 2004;Ahmed, 2005;Nicodemo et al, 2007Nicodemo et al, , 2008. Based on the buffalo cytogenetic map [Iannuzzi et al, 2003] and the most recent fragile site map, some putative orthologous fragile sites in buffalo corresponding to other mammals are included in table 1 .…”

“…Based on the buffalo cytogenetic map [Iannuzzi et al, 2003] and the most recent fragile site map, some putative orthologous fragile sites in buffalo corresponding to other mammals are included in table 1 . Despite their close chromosome-banding homology with cattle, results from buffalo [Nicodemo et al, 2008] and cattle [Rodriguez et al, 2002] were quite different. Several bovine breakpoints orthologous to the most common buffalo fragile sites were apparently observed by Rodriguez and colleagues [2002], but did not reach the significance required for classification of fragile sites.…”

“…Additional high-resolution analyses of aphidicolin-induced breaks in cattle chromosomes will likely be required. One intriguing concept suggested by Nicodemo et al [2008], Iannuzzi et al [2004] and others is the idea that with standardization of chromosomal breakage, and fragile site locations, livestock in pastures could function as bio-markers of environmental contaminants. For implementation of this type of approach, sufficient statistical analyses will be required to establish the base frequency of fragile site expression in comparable unexposed populations.…”