Bioinformatics Analysis and Expression of the Angiopoietin-Like Proteins-4 Gene in Tianzhu White Yak (Bos grunniens)

Angiopoietin-like protein-4 (ANGPTL4) is a member of the ANGPTL family, which is essential for normal metabolic and postnatal development. ANGPTL4 expression is significantly induced by hypoxia. The yak (Bos grunniens) is one of the world's most remarkable domestic animals in alpine hypoxic environment. However, little is known about the existence of yak ANGPTL4 gene and its function. In this study, we used molecular and bioinformatic methods (e. g., cloning, protein structure prediction and multiple sequence alignment, Real-Time quantitative PCR assays, and western blot assays) to examine the structure and function of yak ANGPTL4. We found the cDNA sequence of yak ANGPTLA gene had an open reading frame of 1497 nucleotides, encoding a protein with 498 amino acids. The amino acid sequence of yak ANGTL4 was 99% similarity with Bos taurus, 93% with Ceratotherium simum simum, 41% with Pantholops hodgsonii, Equus caballus, Capra hircus, Camelus ferus, Rattus norveqicus and Homo sapiens, 39% with Ovis aries. The predicted secondary structure of yak ANGPTL4 suggested that this protein was composed of 23 alpha-helixes and 10 beta-sheets. The predicted 3D structure of yak ANGPTL4 reveals overall folding and secondary structures similar to those of H. sapiens. The yak ANGPTL4 contains a calcium binding site that is similar to the one observed in human ANGPTL1 and ANGPTL2. The highest expression level of ANGPTL4 was found in lung, followed spleen, liver, kidney, and muscle, respectively. The lung of yak had substantially greater ANGPTL4 messenger RNA abundance than other tissues (p < 0.05), with measurable but lesser concentrations in the heart. This study, for the first time, reveals the structure and function of ANGPTL4 gene in yak, a specific species and a model animal living in the highland with low oxygen content. The findings would facilitate resistance studies, and benefit yak breeding in similar areas.