Endocrinology and evolution: lessons from comparative endocrinology

Abstract

Comparative endocrinology is the study of the endocrine glands and their hormones in different species of animals. It is undergoing a renaissance because of the new tools and techniques provided by genome sequencing and molecular biology. Until relatively recently, characterization and detection of hormones in lower vertebrates relied on biological assays and protein chemistry approaches, whereas now gene sequences can be readily revealed from whole genome sequencing. Gene expression and synthesis can be used to develop antibodies and other reagents for sensitive assays and revealing physiological experiments can be carried out. Endocrinology traditionally used a range of animal species, including many lower vertebrates. Comparative endocrinology became a separate specialty only in the last 50 years when endocrinologists concentrated on rodents as their model animals. In 1933, Riddle demonstrated that an avian pituitary factor that promoted growth of the pigeon crop-sac was identical to a mammalian pituitary factor that earlier had been found to initiate and maintain milk secretion in mammals. Riddle called this avian factor prolactin and the response of the crop-sac provided a sensitive assay for the detection of human prolactin in pituitary extracts. Pigeon prolactin was the first pituitary hormone to be crystallized and purified in 1937 and led to the purification of mammalian prolactin. Prolactin has a number of roles in lower vertebrates, including a vital role as a hypercalcaemic factor in fish. The first part of this chapter focuses on the calcium-regulating factors including parathyroid hormone (PTH), parathyroid hormone-related protein (PTHrP), and stanniocalcin (STC), and the second part will discuss comparative endocrinology of thyroid hormones and transthyretin (a thyroid hormone distributor in blood the cerebrospinal fluid).