IGF1 mRNA Splicing Variants in Liaoning Cashmere Goat: Identification, Characterization, and Transcriptional Patterns in Skin and Visceral Organs

Insulin-like growth factor I (IGF1) is a member of the insulin superfamily. It performs important roles in the proliferation and differentiation of skin cell and control of hair cycles and is thought to be a potential candidate gene for goat cashmere traits. In this work, we isolated and characterized three kinds of IGF1 mRNA splicing variants from the liver of Liaoning Cashmere goat, and the expression characterization of the IGF1 mRNA splicing variants were investigated in skin and other tissues of Liaoning cashmere goat. The sequencing results indicated that the classes 1w, 1, and 2 of IGF1 cDNAs in Liaoning cashmere goat, each included an open reading frame encoding the IGF1 precursor protein. The deduced amino acid sequences of the three IGF1 precursor proteins differed only in their NH2-terminal leader peptides. Through removal of the signal peptide and extension peptide, the three IGF1 mRNA splicing variants (classes 1w, 1, and 2) resulted in the same mature IGF1 protein in Liaoning cashmere goat. In skin tissue of Liaoning cashmere goat, class 1 and class 2 were detected in all stages of hair follicle cycling, and they had the highest transcription level at anagen, and then early anagen; whereas at telogen both classes 1 and 2 had the lowest expression in mRNA level, but the class 1 appears to be relatively more abundant than class 2 in skin tissue of Liaoning cashmere goat. However, the class 1w transcript was not detected in the skin tissues. Three classes of IGF1 mRNA were transcribed in a variety of tissues, including heart, brain, spleen, lung, kidney, liver, and skeletal muscle, but class 1 IGF1 mRNA was more abundant than classes 1w and 2 in the investigated tissues.