Expression of mRNA encoding growth differentiation factor 9 and
bone morphogenetic protein 15 during follicular formation and
growth in a marsupial, the brushtail possum (Trichosurus vulpecula)
Douglas C. Eckery, Lisa J. Whale, Stephen B. Lawrence, Katherine A. Wylde, Kenneth
P. McNatty, Jennifer L. Juengel *
AgResearch, Wallaceville Animal Research Centre, Ward Street, PO Box 40063, Upper Hutt, New Zealand
Received 3 August 2001; accepted 19 March 2002
The oocyte derived growth differentiation factor (GDF) 9 and bone morphogenetic protein 15 (BMP15; also known as GDF9b)
are essential for normal follicular growth. However, little is known about expression of these factors during ovarian development.
Therefore, we determined the ontogeny of expression of GDF9 and BMP15 mRNA in the developing ovary of the brushtail possum.
Ovaries were collected from pouch young (n 0
5 per group) around times of key developmental events namely: (1) morphological
sexual differentiation (i.e. days 1 Á
5 following birth), (2) after sexual differentiation (i.e. days 10 Á
15), (3) before and during initiation
of germ-cell meiosis (i.e. days 22 Á
45), (4) shortly after initiation of follicular growth (i.e. days 78 Á
85), (5) during preantral follicular
growth (i.e. days 96 Á
113) and (6) during antral follicular growth (i.e. days 155 Á
190). Ovaries were also collected from three juvenile
and four adult animals and gene expression was determined by in situ hybridization. The mRNAs encoding GDF9 and BMP15 were
first observed in oocytes of newly-formed primordial follicles (i.e. days 78 Á
85). Expression of both mRNAs was restricted to the
oocyte and was present in follicles irrespective of whether they were non-growing primordial follicles or undergoing preantral or
antral development. Thus, since the mRNAs encoding GDF9 and BMP15 were not observed until follicular formation, it is unlikely
that these proteins have any role in early germ cell development. Nevertheless, the findings that the mRNAs encoding both proteins
were observed in oocytes from the primordial stage of follicular formation suggest a possible role for these proteins in the
maintenance of primordial follicles as well as a key role during follicular development. These results highlight important species
differences in the ontogeny of expression of GDF9 and BMP15 between possums and other species such as the human, sheep or rat.
# 2002 Published by Elsevier Science Ireland Ltd.
Keywords: Brushtail possum; Ovary; GDF9; BMP15; mRNA
In brushtail possums (Trichosurus vulpecula), gonadal
formation begins at the end of gestation with morpho-
logical sexual differentiation occurring just after birth of
the joey. Germ cells begin to enter the gonad before
birth and meiosis is first observed around day 35 Á
after birth. Formed follicles can be observed starting
around day 50 Á
60 and follicular growth begins by day
70. Antral follicles are consistently observed after
day 160 (Ullmann, 1996; Eckery et al., 1996, 2002a). The
brushtail possum is a mono-ovulatory, polyestrous
seasonal breeder with an estrous cycle of around 26
days consisting of a 16 Á
18 day luteal phase and a 9 Á
day follicular phase (Fletcher and Selwood, 2000).
Primordial, primary, pre-antral and antral stages of
follicular growth can be observed within the ovary with
the ovulatory follicle obtaining a mature size of around
5mm(Eckery et al., 1996; Fletcher and Selwood, 2000).
Thus, many aspects of ovarian formation and follicular
development appear similar between the brushtail
possum and other placental mammals (Eckery et al.,
1996; Ullmann, 1996).
Traditionally, studies examining control of follicular
growth and development have concentrated mainly on
* Corresponding author. Tel.: '
64-4-922-1558; fax: '
E-mail address: email@example.com (J.L. Juengel).
Molecular and Cellular Endocrinology 192 (2002) 115 Á
0303-7207/02/$ - see front matter # 2002 Published by Elsevier Science Ireland Ltd.
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