The Tammar Wallaby And Fur Seal; Comparative Genomics of Animals With Extreme Adaptation to Lactation

Kevin Nicholas 1,2, Matthew Digby 1,2, Christophe  Lefevre 1,2,3,  Julie  Sharp 1,2 , Sonia Mailer 1,2,  Elie Khalil1,2 and Amelia Brennan1,2

1Cooperative Research Centre for Innovative Dairy Products, Melbourne, Australia, 2Department of Zoology, University of Melbourne, Melbourne, Australia, 3 Victorian Bioinformatics Consortium, Monash University, Clayton, Australia.

Comparative genomics is providing opportunities to identify key genes regulating mammary gland development, milk production and composition. The application of this technology to species with extreme adaptation to lactation allows the identification and study of regulatory mechanisms that are present but not readily apparent in other species, and secondly allows the identification of novel molecules and processes for application in the biotechnology market. For example, the tammar wallaby has adopted a reproductive strategy that includes a short gestation (26 days), birth of an immature young and a relatively long lactation (300 days). Both the rate of production and the composition of milk change progressively during the lactation cycle to meet the nutritional demands for investment in considerable development of the pouch young (PY) prior to weaning. The lactating mother, not the sucking pattern of the PY, regulates these changes, which in turn determines the rate of PY growth and development. This greater investment in mammary gland-driven development in marsupials contrasts placental driven development in the eutherian foetus and therefore provides new opportunities to identify factors in the milk regulating growth and development of the pouch young. Interestingly, the tammar can also practise concurrent asynchronous lactation; the mother provides a concentrated milk high in protein and fat for an older animal which is out of the pouch and at heel, and a dilute milk low in fat and protein but high in carbohydrate from an adjacent mammary gland for a newborn pouch young.  Our second study species, the fur seal, has a lactation characterised by a repeated cycle of long at-sea foraging trips (up to 28 days) alternating with short suckling periods of 2-3 days ashore. Lactation almost ceases while the seal is off shore but the mammary gland does not progress to apoptosis and involution.

Our research focus has exploited these models by using microarray analysis and comparative genomics to investigate how mammary function is regulated by endocrine factors, milk and factors intrinsic to the gland. In addition, it is providing new opportunities to identify factors in milk that have a role in the physiological processes regulating growth and development of the young.