THE OXYTOCIN GENE IN GOAT AND SHEEP: STRUCTURE, PROMOTER ANALYSIS AND POLYMORPHISM DETECTION

The oxytocin (OXT) is a very abundant nonapeptide neurohypophysial hormone implicated in several physiological aspects including social, sexual and maternal behaviour, induction of parturition and milk ejection. This study reports the first full characterization of the goat and sheep Oxytocin-Neurophysin I gene, their promoters, amino acid sequences and polymorphism detection. Using the genomic DNA as template, we sequenced and compared the whole Oxytocin–Neurophysin I gene plus 958/960 nucleotides at the 5’ flanking region and 478/477 nucleotides at the 3’ flanking region, in 56 sheep and 29 goat belonging to different breeds/genetic types reared in Italy, Greece, Germany and South Africa. The sheep and goat OXT gene (EMBL LT592265, LT592266) was found to extend over 907 bp, including 510 bp of exonic regions and 397 bp of intronic regions. In both species the gene contains only 3 exons, ranging in size from 153 bp (exon 1) to 202 bp (exon 2). The comparison of obtained sequences showed a high degree of genetic variability at these loci: 16 and 18 polymorphic sites in goat and sheep with a transition/transversion ratio of 4 and 1, respectively. Some of the observed mutations could be responsible for alteration of gene expression. In sheep the SNP g.1879T>A took place inside the polyadenylation site while in goat the g.959G>T would involve the CpG–potential first splice donor site. In particular, we report a first possible example of trans-specific polymorphism at DNA promoter level in goat and sheep (transition g.438T>C) and also the first in a hormone coding gene. This SNP was found both in goat and sheep OXT promoters and it alters a putative binding site of the transcription factor Oct-1. The relative frequency of T allele was of 0.9196 and 0.9138 in sheep and goat, respectively. Through an in vitro reporter assays, we have also demonstrated a significant effect of this SNP on the sheep OXT promoter activity, providing an important contribution to the assessment of its effect on gene expression. Comparison of sequences obtained from the sheep and goat with those available in the database for several other mammalian species revealed several interesting examples of species/breed-specific markers located both in coding and non-coding regions. OXT gene polymorphisms will provide new opportunities to select the best dairy goats and sheep for all the physiological processes controlled by this hormone. Furthermore, the observed differences at OXT loci may be utilized as valuable specie/breed specific markers. The lack of variability at genomic level in sheep and goat OXT gene should be attributed mainly to the paucity of the studies carried out, which represents the real limit for the genetic improvement of these species and therefore, further researches in this direction are necessary to estimate the frequencies of the detected mutations in larger sheep and goat population