Analysis of MTNR1A Genetic Polymorphisms and Their Association with the Reproductive Performance Parameters in Two Mediterranean Sheep Breeds

Abstract

Sheep farming plays an important economic role, and it contributes to the livelihoods of many rural poor in several regions worldwide and particularly in Tunisia. Therefore, the steady improvement of ewes’ reproductive performance is a pressing need. The MTNR1A gene has been identified as an important candidate gene that plays a key role in sheep reproduction and its sexual inactivity. It is involved in the control of photoperiod-induced seasonality mediated by melatonin secretion. The aim of this study was to identify SNPs in the MTNR1A gene in two Tunisian breeds, Barbarine (B) and Queue Fine de l’Ouest (QFO). DNA extracted from the blood of 77 adult ewes was sequenced. Selected ewes were exposed to adult fertile rams. A total of 26 SNPs were detected; 15 SNPs in the promoter region and 11 SNPs in the exon II were observed in both (B) and (QFO) breeds. The SNP rs602330706 in exon II is a novel SNP detected for the first time only in the (B) breed. The SNPs rs430181568 and rs40738822721 (SNP18 and SNP20 in our study, respectively) were totally linked in this study and can be considered a single marker. DTL was associated with SNP18 and SNP20 in (B) ewes (p < 0.05); however, no significant difference was detected between the three genotypes (G/G, G/A, and A/A) at these two SNPs. Fertility rate and litter size parameters were not affected by SNP18 and SNP20. There was an association between these two polymorphisms and (B) lambs’ birth weights (p < 0.05). Furthermore, the ewes with the A/A genotype gave birth to lambs with a higher weight compared to the other two genotypes for this breed (p < 0.05). There was not an association between SNP 18 and SNP20 and (QFO) ewes’ reproductive parameters. These results might be considered in future sheep selection programs for reproductive genetic improvement.

Polymorphism of the MTNR1A Melatonin Receptor Gene in Goat Breeds of Northern Italy

“…Finally, it is interesting to compare our results on the goat species with the most recent advances in the ovine species. Indeed, even in sheep, the most investigated SNPs are rs430181568 (at position g.17355452) and rs406779174 (at position g.17355458) [30]. These are the same polymorphisms that were specifically investigated in our study.…”

“…In sheep species, a polymorphism at the g.17355452 position was found following MnlI enzymatic digestion, which showed a strong link with reduced reproductive seasonality in different Mediterranean breeds. This was shown to be associated with a mutation at the g.17355358 position, which led to an amino acid substitution of Val to Ile, causing a modification in the melatonin signal transmission [30].…”

“…In this study, two polymorphic sites were shown and detected using MnlI and RsaI enzyme digestion [23]. Following this discovery, different studies in sheep have been conducted to investigate the existence of any relationship between MTNR1A gene polymorphism and variation in reproductive performance [25][26][27][28][29][30][31][32][33][34][35]. Specifically, different investigations have shown the presence of a polymorphic cleavage site in the g.17355452 (G > A) position, evidenced by the MnlI enzyme, and in the g.17355458 (C > T) position, evidenced by the RsaI enzyme [36,37].…”

Photoperiod Induces DNA Methylation Changes in the Melatonin Receptor 1A Gene in Ewes

“…Previous studies have shown that polymorphisms in the MTNR1A gene are associated with reproductive seasonality [ 22 , 29 ], reproductive resumption [ 10 ], sexual activity of rams [ 30 ], and lamb birth weights [ 31 ] among sheep. In addition, MTNR1A is expressed in the hypothalamus, pituitary gland, and ovaries in several sheep breeds [ 10 , 11 , 32 ], and a significant difference in the expression of the MTNR1A gene in the hypothalamus between sheep exhibiting year-round estrus and sheep exhibiting seasonal estrus has been reported [ 22 ].…”

Association of melatonin receptor 1 A with litter size in sheep: A review

“…Additionally, melatonin serves to modulate gene expression associated with steroidogenesis, differentiation, and luteinization of granulosa cells. 31 This hormone safeguards the integrity of oocytes and granulosa cells through its specific receptors, MTRN1A and MTRN1B2, by actively scavenging reactive oxygen species (ROS) and regulating apoptosis-related genes, thus preventing apoptosi. 32 …”