MTNR1A, encoding the melatonin receptor 1A, is a crucial gene involved in various biological functions. Melatonin, by binding to MTNR1A, regulates the mammalian circadian rhythm, glucose homeostasis, and reproductive activities. It is also associated with pathways related to cyclic adenosine monophosphate-responsive element-binding protein phosphorylation [1,2,4].

In renal tubular cells, cytoplasmic heterogeneous nuclear ribonucleoprotein L (hnRNPL) post-transcriptionally upregulates MTNR1A RNA through CA-repeat elements in its coding region, protecting it from degradation by exosome component 10 protein. MTNR1A shows a diurnal rhythm in mouse kidneys, with enhanced levels at midnight [1]. In Italian families, three novel variants of MTNR1A were significantly linked to and/or associated with type 2 diabetes [2]. In different Mediterranean sheep breeds, SNPs in the MTNR1A gene exon II affected reproductive performance, such as fertility rate and the duration from ram placement to lambing [3]. In Tibetan sheep, MTNR1A was distributed in the hypothalamus-pituitary-gonadal axis, and its expression in this axis during the estrous cycle was related to the secretion of melatonin and steroid hormones [4]. In buffalo, the expression of MTNR1A in ovarian follicles decreased with the increasing size of the follicle and intrafollicular melatonin concentration, indicating a possible role in folliculogenesis and ovulation [5]. In Tunisian sheep breeds, SNPs in the MTNR1A gene were associated with reproductive performance parameters like birth weight [6].

In conclusion, MTNR1A is essential for regulating circadian rhythms, glucose metabolism, and reproductive functions. Studies on MTNR1A, especially through genetic polymorphism and expression analysis in various animal models, contribute to understanding its role in diseases such as type 2 diabetes and its importance in reproductive regulation in livestock.