Abstract
Changes in the expression of the liver insulin receptor are known to occur in the
rat during postnatal development. To assess whether such changes occur at the level
of gene expression, steady-state levels of insulin receptor mRNA and transcription
rates of the receptor gene have been measured in livers of rats from birth (1 day)
to adulthood (60 days). Northern blot analysis of liver RNA revealed two major insulin
receptor mRNA species of 9.5 and 7.5 kb. When normalized to β actin mRNA, insulin
receptor mRNA levels increased 4-fold between 1 and 15 days, remained stable between
15 and 30 days, and decreased 2-fold between 30 and 60 days. These changes were fully
suppressed by in vivo treatment with actinomycin D, an inhibitor of gene transcription. In vitro nuclear transcription assays showed that the rate of transcription of the insulin
receptor gene increased 2-fold between 1 and 30 days. Insulin receptor concentration
in liver membrane fractions did not exactly parallel insulin receptor mRNA levels
since it increased by 20-30% from 1 to 10 days and decreased 2-fold from 10 to 60
days. During the suckling-weaning transition, insulin receptor mRNA level decreased
2-fold in rats weaned onto a high carbohydrate diet but remained unchanged in rats
weaned onto a high fat diet. Throughout postnatal life, an inverse relationship was
observed between liver insulin receptor mRNA and plasma insulin levels. These results
show that transcriptional changes in insulin receptor gene expression occur postnatally
and suggest that such changes may be insulin-related.
Key words
Insulin - Insulin Receptor - Liver - Gene Expression
