Prolactin action and signalling in the human endometrium

Prolactin is a pleiotrophic hormone that is associated with over 300 biological functions. These functions can be broadly classified into growth and development, immune regulation, metabolism, behaviour and reproduction. The human prolactin gene is located on chromosome 6 and is composed of 6 exons. The gene is approximately 10 kilobases (kb) long whereas the mature prolactin mRNA is about 1 kb in length. Prolactin is encoded by 199 amino acids and the protein is approximately 23 kDa in size. Sequence analysis revealed that prolactin is 40% homologous to growth hormone and placental lactogen. These three proteins are thought to have arisen by duplication of an ancestral gene 400 million years ago. The high sequence homology of these proteins enables prolactin, human growth hormone and placental lactogens to bind the prolactin receptor and activate prolactin intracellular signalling pathways.