In keeping with the evident requirement of insulin-like growth factor I (IGF-I) for normal growth in livestock, IGF-I is required for the normal proliferation of many non-transformed cells in tissue culture. The timing of IGF-I action is believed to be early in proliferation and/or prior to DNA synthesis. Since IGF-I acts on the Type I and Type II IGF receptors, and on the insulin receptor, it is possible that one or all of these receptors are proliferation regulated, such that they are expressed mainly at a certain stage(s) in the cell proliferation cycle. Regulation might occur at the level of the receptor or at the mRNA level. Several cell types have been chosen to test this model. In the experiments reported here, Norden Lab Feline Kidney (NLFK) cells were grown on coverslips and synchronised using a starve/feed regimen. Coverslips fixed at various times after refeeding were probed in situ for the presence of actin RNA and for IGF Type I receptor RNA. Whereas actin RNA levels increased and declined during the proliferation cycle in agreement with earlier reports. Type I receptor RNA levels were undetectable at the times sampled. Possible reasons for this are discussed.
Proceedings of the New Zealand Society of Animal Production, Volume 53, , 377-380, 1993
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