Chapter 2 - The comparative genomics of tammar wallaby and Cape fur seal lactation models to examine function of milk proteins

Abstract

This chapter describes two animals with extreme adaptation to lactation and explores approaches to exploit their unique reproductive strategies to identify new proteins in milk with bioactivity that have the potential to regulate mammary function and growth of the suckled young. The two animal models—the tammar wallaby (Macropus eugenii) and the Cape fur seal (Arctocephalus pusillus pusillus)—are with very different lactation cycles. The tammar wallaby has adopted a reproductive strategy that includes a short gestation of 26.5 days, birth of an immature young, and a relatively long lactation period of 300 days. The composition of the milk changes progressively during the lactation cycle and this is controlled by the mother and not by the sucking pattern of the young. The tammar wallaby can practice concurrent asynchronous lactation demonstrating that the mammary gland is controlled locally. These changes in milk composition control the development of the young and therefore provide new opportunities to identify proteins regulating specific developmental processes in the pouch young. Cape fur seal has a lactation that is characterized by a repeated cycle of long at-sea foraging trips (up to 23 days) alternating with short suckling periods of 2–3 days on-shore. Lactation almost ceases while the seal is offshore but the mammary gland does not progress to apoptosis and involution. It is likely that specific milk proteins have a role both to reduce apoptosis in the mammary gland during foraging and to meet the challenges of growth and fasting physiology of the pup on-shore. Technology platforms using genomics, proteomics, and bioinformatics have been used to exploit these models to identify milk bioactive components.