174. THE EPIDERMAL GROWTH FACTOR (EGF) FAMILY IN THE ENDOMETRIUM AND BLASTOCYST OF THE TAMMAR WALLABY, MACROPUS EUGENII DURING EMBRYONIC DIAPAUSE

Abstract

Embryonic diapause, a suspension of cell division and growth at the blastocyst stage, is widespread amongst mammals, but is especially common in the kangaroos and wallabies. In the tammar, Macropus eugenii, the sequence of endocrine events leading to embryonic diapause and reactivation are well defined [1].  The blastocyst can remain in diapause for up to 11 months without cell division, measurable metabolism or apoptosis occurring [2]. The ovarian hormones, especially progesterone, exert their effects on the blastocyst by alterations in the endometrial secretions [3], but the molecular cross-talk between the endometrium and blastocyst is unknown. There is increasing evidence for the involvement of leukaemia inhibitory factor (LIF) but the epidermal growth factor (EGF) family of growth factors are also likely to be involved. This study examined the expression of EGF and HB-EGF as well as their receptors, ERBB1 and ERBB4, in the tammar endometrium and blastocyst at entry into, and reactivation from, diapause. The genes for these factors were highly conserved in the tammar with orthologues in human and mouse. Quantitative RT-PCR of all four factors in the endometrium showed that expression changed with stage. Although expression levels of both receptors did not change between diapause and reactivation, both HB-EGF and EGF levels increased at reactivation from diapause and levels of HB-EGF decreased at entry into diapause. All factors were immunopositive in the endometrium. Studies underway will determine whether the cellular location and quantity of these factors change with entry into or exit from diapause, and define the molecular interactions occurring between the blastocyst and endometrium. These results are consistent with a role for the EGF family of growth factors in the control of embryonic diapause in tammars.