DISTINCT EXPRESSION PATTERNS OF INSULIN-LIKE GROWTH-FACTOR BINDING-PROTEINS 2 AND 5 DURING PETAL AND POSTNATAL-DEVELOPMENT

Insulin-like growth factors (IGFs), when isolated from serum or tissue fluids, are usually found as part of a protein complex which also con tains one of several IGF binding proteins (IGFBPs). Although some IGFB Ps have been shown to alter interactions of IGFs with their receptors in vitro and can modify the responses of cultured cells to exogenous I GFs, the in vivo functions of IGFBPs remain unclear. This study examin es expression of a recently described IGFBP gene, IGFBP-5, in the rat embryo and fetus and in selected adult tissues. Embryonic IGFBP-5 mess enger RNA (mRNA) can be detected as early as embryonic day 10.5 and ha s an mRNA expression pattern distinct from the previously characterize d pattern of IGFBP-2 mRNA expression. Major sites of IGFBP-5 expressio n during early postimplantation stages of development include the noto chord, the floor plate, regions of the surface ectoderm, muscle precur sor cells, and specific axial regions of neuroepithelium. Later in dev elopment IGFBP-5 mRNA is found in several regions of the central nervo us system, including the proliferative zone of the external granule la yer of the cerebellum and the mitral neurons of the olfactory bulb, as well as in muscle precursor populations of the developing limb, and i n most cells of the anterior pituitary. In addition, only a subset of pituicytes in the adult posterior pituitary express IGFBP-5, which pro vides the brst evidence that this cell population is biochemically het erogeneous. Taken together, these data suggest functions for IGFBP-5 d uring development of several organ systems.