Identification of transition bias in oxidized low density lipoprotein receptor 1 gene in buffalo

Background and aim: Though transition bias has been previously demonstrated in cattle, however, there has not been any study that has explored transition bias in buffalo nuclear genome. The aim of the present study was to evaluate the nucleotide substitution pattern in the Intron I of Oxidised Low Density Lipoprotein Receptor 1 (OLR1) gene in four breeds of Indian buffalo using 24 different nucleotide substitution models and evaluate their association with DNA methylation. Materials and Methods: Transition/transversion bias (R) was estimated by 24 different nucleotide substitution models available in MEGA 5.0. The transition/transversion bias (R) was estimated under the Kimura 2-parameter model. Substitution patterns and the transitions/transversions rates (r) were then estimated by Tamura-Nei-I and Tamura-Nei-II models. The CpG Island search was done by using CpG Plot Island online Software available at European Bioinformatics Institute (EBI) website. Results: The frequency of transition was found to be 3.5 times higher than that of the transversion mutation frequency. Out of 9 nucleotide substitutions, 7 transitions and 2 transversions were found. Among all the nucleotide substitutions, thymine to cytosine substitutions was observed to be very high. CpG Island search tool revealed that IntronI of OLR1 genes is a CpG rich region, thus prone to methylation. Conclusions: Higher transition frequency was found in the intronI of OLR1 gene, however due to the richness of methylated CpGs in the evaluated stretch of genome, the higher T C transitions could likely be a result of frequent deaminations of the methylated cytosines into thymines during the evolution of four buffalo breeds.