RESEARCH ARTICLE SUMMARY
◥GERM CELL DEVELOPMENT
ZGLP1 is a determinant for the oogenic fate in mice
So I. Nagaoka, Fumio Nakaki, Hidetaka Miyauchi, Yoshiaki Nosaka, Hiroshi Ohta,
Yukihiro Yabuta, Kazuki Kurimoto, Katsuhiko Hayashi, Tomonori Nakamura,
Takuya Yamamoto, Mitinori Saitou*
INTRODUCTION:Mammals generate sexually di-
morphic germ cells, oocytes and spermatozoa,
which form the basis for sexual reproduction.
Studies in mice have shown that in embryonic
ovaries, retinoic acid (RA) and its downstream
effector, STRA8, induce sexually uncommitted
germ cells into the oogenic fate, whereas in
embryonic testes, RA is degraded by Sertoli
cells and other mechanisms elicit the sper-
matogenic pathway. Conversely, our recent
study has shown that RA and STRA8 are not
sufficient to induce in vitro mouse primordial
germ cell–like cells (mPGCLCs) into the oogenic
fate. Instead, bone morphogenetic protein
(BMP), which is expressed in granulosa cells,
and RA synergistically confer the oogenic path-
way on mPGCLCs. This finding creates an
experimental framework for a systematic un-
derstanding of the mechanism of oogenic fate
determination.
RATIONALE:Using mouse embryonic stem cells
(mESCs) as a starting material, our in vitro
system reconstitutes PGCspecification, epige-
netic reprogramming, and oogenic fate de-
termination under a defined condition. We
reasoned that this system should serve as a
powerful platform with which to analyze the
mechanism of germ cell development, includ-
ing that for oogenic fate determination. Here,
we set out to identify a transcriptional regula-
tor that functions downstream of BMP signal-
ing for oogenic fate determination by screening
with RNA sequencing and to explore the regu-
lation and function of a key candidate using
both the in vivo model and the in vitro sys-
tem through loss- or gain-of-function experi-
ments. We reasoned that these experiments
should clarify the distinctive functions of
the BMP and RA pathways in oogenic fate
determination.RESULTS:We identifiedZglp1,whichencodes
an evolutionary conserved transcriptional reg-
ulator with GATA-like zinc fingers, as a gene
that showed specific up-regulation in mPGCLCs
in response to BMP, but not to RA. In females,
ZGLP1 showed specific and transient expression
in embryonic germ cells during oogenic fate
determination [from embryonic day (E) 12.0 to
E15.5], whereas in males, it was not detected in
embryonic germ cells undergoing spermato-
genic fate determination but was expressed in
postnatal undifferentiated or differentiatingspermatogonia. In females,Zglp1was essen-
tial for the oogenic fate determination, with
no germ cells differentiating into oocytes in
the meiotic prophase inZglp1-knockout mice,
whereas in males, it was dispensable for germ
cell sex determination but was required in
the spermatogonia for an efficient completion
of meiotic prophase. ZGLP1 overexpression
replaced the functions of the BMP signal-
ing and induced mPGCLCs into the oogenic
fate and meiotic prophase with up-regulation
ofStra8intheabsenceofRA.Wefoundthat
the key role of RA signaling was to contrib-
ute to maturation of the overall oogenic pro-
gram and to repression of
the PGC program. Con-
sistently,Zglp1showed
a broad regulatory cover-
age of the transcriptome
for the oogenic program,
which included the pro-
gram for RNA processing, transcription and
chromatin modification, retrotransposon reg-
ulation, meiosis, andoocyte development,
whereasStra8, which functioned in part down-
stream ofZglp1, mainly regulated the meiotic
program. Chromatin immunoprecipitation se-
quence analysis suggested that ZGLP1 pref-
erentially activates key genes repressed by
Polycomb activities in sexually uncommitted
germ cells.CONCLUSION:Our results demonstrate that
BMP signaling and ZGLP1 play a central
role in establishing the key programs for
the oogenic fate, with RA signaling assist-
ing in the maturation of these programs,
including repression of the early PGC pro-
gram. These findings provide an integrated
paradigm for mammalian oogenic fate de-
termination. The distinct function of ZGLP1
betweenfemalesandmalesrepresentsa
sexual dichotomy of the mechanism for the
onset and progression of the oogenic and
spermatogenic processes, including meiosis.
A better understanding of the mechanism
of sex determination in germ cells should
serve as a key, not just for further promot-
ing in vitro gametogenesis (IVG) studies,
including human IVG, but also for delin-
eating the etiology of critical diseases such
as infertility and genetic and epigenetic dis-
orders of offspring. Furthermore, an in vitro
system that induces meiotic recombination
in a physiologically relevant context propels
future studies to understand the mechanisms
for generating genetic diversity.
▪RESEARCH
Nagaokaet al.,Science 367 , 1089 (2020) 6 March 2020 1of1
The list of author affiliations is available in the full article online.
*Corresponding author. Email: [email protected].
kyoto-u.ac.jp
Cite this article as S. I. Nagaokaet al.,Science367,
eaaw4115 (2020). DOI: 10.1126/science.aaw4115.ZGLP1 induces the oogenic fate in mice.Images show immunofluorescence staining of SYCP3 (yellow)
and DDX4 (magenta) expression in E15.5 oocytes (left) and mPGCLCs in vitro overexpressing ZGLP1
(right). ZGLP1 alone, which acts downstream of the BMP signaling, is sufficient to induce mPGCLCs into
oocyte-like cells in the meiotic prophase with SYCP3-positive synaptonemal complexes. Scale bar, 10μm.
ON OUR WEBSITE◥Read the full article
at http://dx.doi.
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