Science_-_6_March_2020

RESEARCH ARTICLE SUMMARY

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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 differentiating

spermatogonia. 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.

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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.

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science.aaw4115

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