Exon 3 of the growth hormone receptor (GH-R) is specific to eutherian mammals

Abstract

Growth hormone receptor (GH-R) plays a critical role in the control of growth and metabolism in all vertebrates. GH-R consists of 9 coding exons (2-10) in all eutherian mammals, while the chicken only has 8 coding exons, and does not have an orthologous region to exon 3 in eutherians. To further understand the evolutionary origins of exon 3 of the GH-R in eutherians we cloned the full-length GH-R sequence in a marsupial, the tammar wallaby to determine whether exon 3 was present or absent in marsupial liver cDNA. There was no evidence for the presence of an exon 3 containing mRNA in sequence of tammar pouch young and adult livers. We next examined the genomes of the platypus (a monotreme mam..