DNA polymorphism of leptin gene in Bos indicus and Bos taurus cattle

Leptin plays an important role in the regulation of feed intake, energy metabolism, growth and reproduction of cattle. We used the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique to screen for DNA polymorphisms of the leptin gene in 403 cattle belonging to various breeds of Bos indicus (Hariana, Sahiwal, Gir and Nimari cattle), Bos taurus (Holstein Friesian (HF) and Jersey cattle) as well as Bos taurus x Bos indicus crossbreds (1⁄2 HF x 1⁄2 Hariana). In all the cattle we amplified two regions of the leptin gene, a 522 bp fragment comprising the partial intron 2 and exon 3 and another 94 bp fragment consisting of part of exon 2. Digestion of 522 bp PCR products with the BsaAI restriction enzyme revealed three genotypes in all the breeds of cattle studied. This is the first report of the presence of leptin gene polymorphism in purebred Bos indicus cattle of Indian origin (indicine cattle). Almost similar gene and genotype frequencies were observed in all the breed groups, while the frequency of mutant homozygotes (AA) was very low (0.03 to 0.07). On digestion of the 94 bp fragment with the Kpn2I restriction enzyme, three genotypes were observed in HF, Jersey and crossbred cattle. The CC genotype had the highest frequency (0.68) in crossbreds whereas the frequency of CT heterozygotes was highest (0.69) in HF cattle. This mutation was absent in all the breeds of indicine cattle. The results suggest that the BsaAI-RFLP mutation has occurred far back in evolution before the divergence of taurine and indicine cattle while the Kpn2I mutation has occurred recently as indicated by the fact that this mutation was only detected in taurine cattle.