Expression and location of IGF binding proteins-2,-4, and-5 in developing fetal tissues

Insulin-like growth factors are associated with myogenesis in vivo, and the ir actions are mediated by IGF binding proteins (IGFBP). Sites of IGFBP pro duction and their location during early development are not clear. The obje ctive of this research was to examine the developmental expression and loca tion of IGFBP-8, -4, and -5 mRNA and peptides in developing porcine skeleta l muscle and liver. Pregnant pigs were euthanatized at various times postco nception (pc). Developmental expression of IGFBP was evaluated using total RNA extracted from skeletal muscle and liver of 30-, 44-, 59-, 68-, 75-, 89 -, and 109-d pc fetuses and from adult and neonatal pigs. Localization of I GFBP-8, -4, and -5 mRNA and peptides was examined by in situ hybridization and immunocytochemistry of muscle samples from contralateral pelvic limbs o f each pig. Overall muscle IGFBP gene expression decreased (P < .05) with i ncreasing age. Moreover, expression of liver IGFBP-8 and -5, but not of IGF BP-4, was greater(P < .05) during prenatal than during postnatal periods. T he majority of immunoreactive IGFBP was located in developing muscle cells, with little localized to connective tissue, except at later stages of deve lopment. These data show that IGFBP-8, -4, and -5 expression is time- and t issue-dependent in fetal liver and muscle.