Molecular Cloning, Characterisation, Tissue Distribution, and mRNA Expression Changes under Different Light Regimes of Brain and Muscle Arnt-Like Protein-1 (BMAL1) in Columba Livia

Abstract

Brain and muscle Arnt-like protein-1 (BMAL1) plays an important role in circadian rhythm, which is involved in daily behaviours and physiological activities. However, little is known about the molecular function of BMAL1 in the Pigeon ( Columba livia). In our study, the full-length cDNA of Bmal1 was cloned and sequenced from the Pigeon for the first time, and submitted to the GenBank to obtain the accession number (KF906247). The full-length cDNA of Bmal1 consists of 2,488 nucleotides, and encodes 634 amino acids. Phylogenetic analysis showed that it bore the greatest similarity to Bmal1 from the Chicken ( Gallus gallus) and Barn Owl ( Tyto alba). The amino acid sequence of the Pigeon BMAL1 contained a HLH domain and two PAS domains, which are involved in forming hetero-homodimers with the CLOCK as the positive element of the circadian rhythm. The results of real-time quantitative PCR of Bmal1 under different light regimes showed that the amplitude and expression pattern of Bmal1 were strongly affected by day length. Bmal1 was most highly expressed in the pancreas. Relative to Bmal1 expression level under 12 h of light exposure, it was increased significantly in the pituitary gland, ovary and uterus under 15 h of light exposure ( P < 0.05). However, other tissues, including the hypothalamus, heart, liver, spleen, kidney, intestines, crureus, and pectorals exhibited no significant difference ( P < 0.05) under the two light regimes. This is the first study to investigate Bmal1 mRNA levels in various tissues under different light cycles, and thereby provide data for further study of the molecular and regulatory mechanisms of Bmal1 and circadian clock genes of the Pigeon.