Chicken insulin-like growth factor binding protein (IGFBP)-5: conservation of IGFBP-5 structure and expression during evolution.

A complementary DNA (cDNA) clone encoding chicken insulin-like growth factor binding protein-5 (cIGFBP-5) was isolated. The nucleotide sequence of the 1236-bp clone encodes a mature polypeptide of 251 amino acids with a calculated molecular weight of approximately 28.2 kDa. The deduced amino acid sequence is 83% identical to human IGFBP-5. Labeled cIGFBP-5 cDNA detected a single mRNA transcript of approximately 6 kb by Northern blot analysis of various tissues obtained from embryonic and 6 weeks post-hatch chickens; interestingly, adult heart showed an approximately 10-fold increase in cIGFBP-5 mRNA relative to embryonic heart. The pattern of IGFBP-5 mRNA expression in chicken tissues was similar to that found in mammals during fetal and extrauterine life. In addition, IGFBP-5 mRNA was abundant in primary cultures of chicken myoblasts throughout in vitro differentiation and fusion. The conservation of IGFBP-5 primary structure and expression pattern across vertebrate species suggests conservation of important functions during evolution, particularly in muscle differentiation.