Molecular control of embryonic diapause in the tammar wallaby

© 2016 Dr Florine Cynthia MartinThe marsupial tammar wallaby has the longest period of embryonic diapause of any mammal, up to 11 months, during which there is no cell division or blastocyst growth. Since the blastocyst in diapause is surrounded by acellular coats, the signals that maintain or terminate diapause involve factors which reside in uterine secretions. The molecular communication that occurs between the endometrium and the embryo is essential to control the events of embryonic diapause downstream of the uterine endocrine signals. However, it is still unclear how factors secreted from the endometrium affect the blastocyst to control embryonic diapause. Entry into diapause may be caused by a decrease in secretory growth factors and their receptors from or within the endometrium, while their increase may induce reactivation by removal of cell cycle inhibition in the endometrium. In addition, it is known that metabolic quiescence occurs during diapause, for an extended period when the uterus itself is quiescent. It is possible that the embryo survives on factors secreted by the endometrium during this period. This study aimed to profile and quantitate the essential factors in both the endometrium and the uterine flushing, to further our understanding of the molecular control of embryonic diapause. In this study, uterine flushings (UF) and endometrium were used to assess changes in uterine secretions of tammars using liquid chromatography-mass spectrometry (LC-MS/MS) during diapause (day 0 & 3) and reactivation days 4, 5, 6, 8, 9, 11 and 24 after removal of pouch young (RPY), which initiates embryonic development. This study supports earlier suggestions that the presence of specific factors stimulate reactivation, early embryonic growth and cell proliferation. Mitogen related proteins like hepatoma-derived growth factor(HDGF), soluble epidermal growth factor receptors (sEDGFR) and few others regulated by progesterone and oestrogen were present after d3 concomitant with the start of blastocyst mitoses at d4. Proteins involved in p53(tumour protein p53)/CDKN1A (Cyclin dependent kinase inhibitor 1 or p21) cell cycle inhibition pathway were observed in the uterine flushings and endometrium from animals in diapause. We propose that once the p21 inhibition of the cell cycle is lost, growth factors including HDGF and EGFR are responsible for reactivation of the diapausing blastocyst via the uterine secretions