Stability of alternatively spliced IGF-I mRNA in growth plate chondrocytes

Insulin-like growth factor-I (IGF-I) enhances the proliferation and hypertr ophy of growth plate chondrocytes leading to increased growth plate width t hus promoting bone elongation. Differing quantities of the multiple IGF-I t ranscripts within the growth plate suggest differential regulation of IGF-I , To assess this, the relative stabilities of the 1Ea, 1Eb, and 2Ea IGF-I m RNA classes in 2-6 week old rat growth plates were evaluated. The mean esti mated half-life of class 1Ea was 3.7 +/- 0.05 h, while classes 1Eb and 2Ea decayed gradually over the course of the experiment. Estimated half-lives f or each IGF-I mRNA species were unchanged at all ages examined. Incubation with Act D enhanced the transcription of class 1Ea, 1Eb, and 2Ea mRNAs to v arying degrees. This implies that the differential stability of alternative IGF-I mRNA classes may be an inherent regulatory component that is not inf luenced by an animal's developmental state, and the differential abundance of alternative IGF-I mRNA species in the growth plate throughout developmen t is due to transcriptional differences.