EXPRESSION OF SOMATOTROPIN RECEPTOR MESSENGER-RIBONUCLEIC-ACID IN BOVINE-TISSUES

The somatotropin receptor mRNA is controlled by at least two different gene promoters that generate two variants with different exon 1 seque nces (1A and 1B). The location of 1A and 1B somatotropin receptor mRNA within cattle tissues and, hence, the tissue specificity of the 1A an d 1B promoters are unknown. In addition, the cDNA sequence of the 1B s omatotropin receptor has not been determined. Our objective, therefore , was to sequence a cDNA for the 1B somatotropin receptor and to analy ze bovine tissues for expression of 1A and 1B somatotropin receptor mR NA. Twenty adult tissues and six fetal tissues were collected at slaug hter from each of four cows and two fetuses. Messenger RNA was analyze d using ribonuclease protection assays. The adult liver expressed both 1A and 1B mRNA. All other adult tissues expressed 1B mRNA but not 1A mRNA. The greatest amount of 1B mRNA was detected in liver and adipose (abdominal and subcutaneous) tissues. Other tissues had approximately one-half to one-tenth of the amount of 1B mRNA in the liver or adipos e tissue. Fetal tissues (including fetal liver) expressed 1B mRNA and not 1A mRNA. Based on cDNA sequencing, the protein encoded by the 1A a nd 1B mRNA was nearly identical. We concluded that 1A somatotropin rec eptor mRNA is specific to adult bovine liver. Other adult and fetal bo vine tissues expressed 1B somatotropin receptor mRNA with a predicted protein sequence that was similar to the 1A somatotropin receptor.