The tammar wallaby: A model to examine endocrine and local control of lactation

Abstract

SummaryMarsupials, such as the tammar wallaby (Macropus eugenii), have adopted a reproductive strategy that is very different to eutherians. Both the rate of production and the composition of milk changes progressively during the lactation cycle to meet the nutritional demands of an altricial young. The tammar therefore provides a valuable model to study changes in milk composition, and in particular the genes that code for proteins secreted in the milk, to more accurately assess the role of gene products regulating either development of the young or mammary function. IUBMB Life, 59: 146-150, 2007 Keywords Marsupial; milk protein; WAP; involution; lactation; neonate; mammary; milk. THE TAMMAR AS A MODEL SYSTEM TO STUDY LACTATIONMost of our laboratory and livestock species have been subject to intense selective breeding for many decades to improve the quality of milk produced -but can the wallaby reveal its ancient secrets of regulating lactation to increase our understanding of the lactation cycle? The increasingly popular approach of bioprospecting for genes and bioactive molecules from native animals and plants provides new resources for the advancement of agriculture and biotechnology. The application of new technology to species with unusual reproductive strategies allows the identification and study of regulatory mechanisms and molecules that are present but not readily apparent in other species.Marsupials, such as the tammar wallaby (Macropus eugenii), have adopted a reproductive strategy that is very different to eutherians (1, 2). It includes a short gestation of 26 days, birth of an immature young and a relatively long lactation of 300 days. Both the rate of production and the composition of milk, particularly the proteins, change progressively during the lactation cycle to meet the nutritional demands required for the considerable development of the pouch young prior to weaning (Fig. 1a). We know that the lactating tammar regulates these changes in milk composition, which in turn determines the rate of pouch young growth and development. If a pouch young at an early stage of lactation is transferred to the mammary gland of a tammar at a later stage of lactation, the fostered young will grow and develop at an accelerated rate (3). Much of the equivalent development in eutherians occurs in utero. Therefore it is possible that many of the biological factors that regulate development of eutherian embryos are delivered in the milk by the mammary gland of marsupials. This allows researchers to access all the bioactives in milk, to examine the processes by which the mammary gland produces these factors and examine their potential function.Monotremes, extant egg laying mammals (platypus and echidna), and marsupials both begin consuming milk at a very

Acute involution in the tammar wallaby: Identification of genes and putative novel milk proteins implicated in mammary gland function

“…In addition to acting independently to produce milk of different composition, the two adjacent mammary glands involute at different times. This further supports the concept that mammary function is regulated by local factors, most likely by milk proteins that act through an autocrine mechanism [53].…”

The miR‐379/miR‐410 cluster at the imprinted Dlk1‐Dio3 domain controls neonatal metabolic adaptation

“…Pathways deregulated in ΔMat neonates mostly relate, but are not restricted, to aspects of lipid metabolism that are crucially engaged when a suckling‐based, lipid‐rich diet is initiated. In marsupials, milk composition changes gradually during the course of lactation (Brennan et al , ). This is in striking opposition to eutherians, which have to adapt to an abrupt transition in energy substrates.…”

Evolution of Lactation: Ancient Origin and Extreme Adaptations of the Lactation System

“…Marsupial milk provides essential nutrients and putative growth factors for the development of the young, and cross-fostering experiments have shown that milk controls postnatal development (4,95). Endocrine and other factors, potentially intrinsic to the mammary gland, are likely to control milk secretion (36), and marsupial milk contains autocrine/paracrine regulators of the mammary gland (11,67). In special circumstances, macropod marsupials (kangaroos and wallabies) such as the tammar wallaby (Macropus eugenii) and red kangaroo (Macropus rufus) may present ACL, feeding two young of different ages concurrently with milk of different compositions from adjacent mammary glands, a newborn pouch young and one a few months older (51,68).…”