The nucleotide sequence of chicken Mx cDNA was reported earlier using the White Leghorn breed in Germany, but it showed no enhanced resistance to viruses. In this study, the nucleotide sequences of chicken Mx cDNA were determined in many breeds. A total of 25 nucleotide substitutions, of which 14 were deduced to cause amino acid exchanges, were detected, suggesting that the chicken Mxgene is very polymorphic. Transfected cell clones expressing chickenMx mRNA were established after the Mx cDNA was constructed with an expression vector and introduced into mouse 3T3 cells, and the Mx genes from some breeds were demonstrated to confer positive antiviral responses to influenza virus and vesicular stomatitis virus. On the basis of the comparison among the antiviral activities associated with many Mx variations, a specific amino acid substitution at position 631 (Ser to Asn) was considered to determine the antivirally positive or negative Mx gene. Thus, a single amino acid substitution influences the antiviral activity of Mx in domesticated chickens.

Cold exposure produces adaptive hyperplasia and growth of brown adipose tissue (BAT), the major site of non-shivering thermogenesis in rodents, associated with increased angiogenesis in this tissue. Vascular endothelial growth factor (VEGF), one of the most potent angiogenic factors, was found to be expressed abundantly in BAT of the rat. When rats were exposed to cold at 4 °C, the VEGF mRNA level in BAT was increased by 2-3-fold in 1-4 h, but returned to the basal level within 24 h. VEGF expression in other tissues such as heart, kidney and lung did not change after cold exposure. The cold-induced increase in VEGF mRNA was abolished by surgical sympathetic denervation, but mimicked by administration of noradrenaline or a β₃-adrenoceptor agonist CL316,243, indicating the critical role of the β-adrenergic pathway in VEGF expression in BAT. Among three isoforms of VEGF, the mRNA of a short form (VEGF120) lacking heparin-binding activity was preferentially increased after cold exposure and treatment with the adrenergic agonists. These results suggest that cold exposure activates the sympathetic nerves and leads to a rapid increase in synthesis of VEGF in BAT, which in turn stimulates the proliferation of surrounding vascular endothelial cells.

Wild-type or mutated human β3-adrenergic receptor (Trp64Arg) cDNAs were stably expressed in mouse 3T3-L1 cells. Saturation binding study using a β-adrenergic ligand revealed that there was no significant difference in the receptor density and the equilibrium dissociation constant between the two cell lines. However, the ability of the mutant β3-adrenergic receptor to accumulate cyclic AMP (cAMP) in response to isoproterenol was much reduced and Kact for cAMP accumulation was lowered as compared to the wild type receptor. The amount of alpha subunit of stimulatory GTP-binding protein (GSα) and adenylyl cyclase activity in response to forskolin were not different in the two cell lines. The responses of the mutant receptor to epinephrine, norepinephrine and L-755,507, a highly specific agonist for human β3-adrenergic receptor, were also reduced, but the reduction of Kact for L-755,507 was more evident than other agonists tested. The cAMP accumulation in response to some conventional β3 agonists was less than 10% of that to isoproterenol even in the cells expressing the wild type receptor. These results suggest that the Trp64Arg mutant β3-adrenergic receptor has less ability to stimulate adenylyl cyclase, and that lipolytic activity through the β3-adrenergic receptor by catecholamines in subjects carrying this mutation might be suppressed.