NUTRITIONAL REGULATION OF INSULIN-LIKE GROWTH-FACTOR-I RECEPTOR MESSENGER-RNA LEVELS IN GROWING CHICKENS

Insulin-like growth factor-I (IGF-I) exerts its effect through the IGF -I receptor. To investigate the effects of nutritional status on chick en IGF-I receptor gene expression, a solution hybridization/RNase prot ection assay for IGF-I receptor mRNA was developed, A cDNA clone corre sponding to the carboxyl-terminal region of the IGF-I receptor was obt ained by reverse transcription-PCR (RT-PCR). Sequence analysis of the clone showed that this region of the chicken IGF-I receptor is highly divergent from the human IGF-I receptor, IGF-I receptor mRNA was detec ted in all tissues examined from newly hatched chickens. The rank orde r of the IGF-I receptor mRNA levels was liver < thigh muscle < stomach < heart < lung < kidney < brain. In 1-week-old chickens, 5 days of st arvation caused a 2.5- to 3-fold increase in the mRNA in muscle and ki dney, Starvation of 4-week-old chickens for 5 days caused a 1.7 to 2.2 -fold increase in IGF-I receptor mRNA levels in kidney, liver, and mus cle, In contrast, IGF-I receptor mRNA levels in brain failed to change . The mRNA levels were reduced to the control level by refeeding of th e starved chickens for 24 h. These data suggest a tissue- and developm ent-specific response of chicken IGF-I receptor gene expression to nut ritional status.