TISSUE-SPECIFIC EXPRESSION OF THE INSULIN-LIKE GROWTH-FACTOR BINDING-PROTEIN (IGFBP) MESSENGER-RNAS IN MOUSE AND RAT DEVELOPMENT

The insulin-like growth factor binding proteins (IGFBPs) are polypepti des which are thought to modulate the bioactivity of IGF-I and IGF-II, and may also have activities independent of the IGFs. The expression patterns of IGFBPs-1, -3, -4, and -6 in midgestational rodents were an alyzed using in situ hybridization to begin to characterize the role o f these IGFBPs during development. All IGFBPs are expressed at least a s early as rat embryonic day 14 (e14), and each has a unique pattern o f expression. IGFBP-1 mRNA is expressed by the liver throughout mid an d late gestation. IGFBP-3 mRNA is expressed at high levels in the urog enital tract, several muscle groups, and the nasal epithelia. IGFBP-3 transcripts are also expressed at lower levels by many non-neural tiss ue types, including the liver, stomach, and heart. IGFBP-4 is abundant ly expressed by many tissues in the developing embryo, with the notabl e exceptions of the spinal cord, specific cartilage groups, and the th ymic cortex. IGFBP-6 is expressed in the liver by e14, and also by a p reviously unrecognized cell population surrounding developing cartilag e. Taken together these observations suggest distinct roles in develop ment for each of the IGFBPs.