To determine whether a link exists between reproductive seasonality and the structure of the melatonin receptor 1A (MTNR1A) gene, the latter was studied in nonseasonal estrous breeds (Small Tail Han and Hu ewes) and seasonal estrous breeds (Dorset, Suffolk and German Mutton Merino ewes). A large fragment of the exon 2 of the MTNR1A gene was amplified and a uniform fragment of 824 bp was obtained in 239 ewes of five breeds. The 824 bp PCR product was digested with restriction endonucleases Mnl I and Rsa I, and checked for the presence of restriction sites. The presence (allele M) or absence (allele m) of an Mnl I site at base position 605 led to three genotypes MM (236 bp/236 bp), Mm (236 bp/303 bp) and mm (303 bp/303 bp) in five sheep breeds. The presence (allele R) or absence (allele r) of a Rsa I site at base position 604 led to three genotypes RR (267 bp/267 bp), Rr (267 bp/290 bp) and rr (290 bp/290 bp) in five sheep breeds. Frequencies of MM and RR genotypes were obviously higher, and frequencies of mm and rr genotypes were obviously lower in nonseasonal estrous sheep breeds than in seasonal estrous sheep breeds. Sequencing revealed four mutations (G453T, G612A, G706A, C891T) in mm genotype compared to MM genotype and one mutation (C606T) in rr genotype compared to RR genotype. For polymorphic Mnl I and Rsa I cleavage sites, the differences of genotype distributions were very highly significant (p<0.01) between Small Tail Han ewes and seasonal estrous sheep breeds. In each group, no significant difference (p>0.05) was detected. These results preliminarily showed an association between MM, RR genotypes and nonseasonal estrus in ewes and an association between mm, rr genotypes and seasonal estrus in ewes.

The b-3 adrenergic receptor (ADRB3) is a G-protein coupled receptor involved in regulating lipolysis, as part of homeostatic regulation. In this study, South African Mutton Merino and Shanxi Dam Line were used to study the distribution and quantification of ADRB3 in adipose (subcutaneous, omental, retroperitoneal, mesenteric and perirenal fat) and non-adipose (heart, liver, spleen, lung and kidney) tissues of sheep. The protein was determined by immunohistochemical technique and by mRNA abundance via real-time polymerase chain reaction. ADRB3 was detected in all studied tissues with abundance in adipose tissues higher than in non-adipose tissues ( P , 0.001). For adipose tissues, greater expression was found in deep deposits such as great omental and retroperitoneal fat than in subcutaneous fat ( P , 0.05). Significant differences ( P , 0.05) both for mRNA and for protein expression also existed between the two sheep flocks. These findings are consistent with the known function of ADRB3 in mediating lipolysis and homeostasis in adipose tissues.Keywords: b-3 adrenergic receptor, sheep, tissues, mRNA expression, immunohistochemistry ImplicationsIn this study, the b-3 adrenergic receptor (ADRB3) expression in various tissues of sheep was detected by immunohistochemical technique and by mRNA abundance via real-time PCR. Despite its low expression, the presence of ADRB3 in the spleen and kidney was found in livestock for the first time. Generally, ADRB3 expressed higher in adipose than in non-adipose tissues, and for the former, it was higher in deep fat deposits than in subcutaneous fat. The distributions are consistent with the known functions of ADRB3 in mediating lipolysis and homeostasis in adipose tissues, and relaxation of vascular smooth muscle in the cardiovascular system. The relation between low expression and its function in some viscera, for example, lung, spleen and kidney of sheep deserves further study.Introduction b-Adrenergic receptors (ADRBs) are G-protein coupled receptors that mediate effects of the endogenous catecholamines adrenaline and noradrenaline. Three subtypes of ADRBs have been identified, named ADRB1, ADRB2 and ADRB3, respectively. These receptors are present in most mammalian tissues, but the distribution of each subtype varies among tissues in a given species. Among the various physiological roles of ADRBs, the ADRB3 subtype mediates lipolysis and stimulates thermogenesis in adipose tissues (Cannon and Nedergaard, 2004) by activating uncoupling protein in mitochondria.In early studies, ADRB3 was identified mainly on the surface of white and brown adipocytes as reviewed by Strosberg (1997). In recent years, expression of the protein was also found in the human heart (Rozec and Gauthier , (Rodriguez et al., 1995).It has been confirmed that the mRNA of the ADRB3 gene is expressed in various tissues of domestic animals. The 2.0 kb ADRB3 transcript in the bovine brown adipose tissue (PietriRouxel et al., 1995), and two transcripts of 2.2 and 1.9 kb in porcine subcutaneous fat (McNeel and ...