PAX4
−/−
single-knockout and ZNF800
−/−
;PAX4
−/−
double-knockout organoids (Fig . 4D and fig.
S19, A and B). Reintroduction of PAX4 in
ZNF800
−/−
;PAX4
−/−
organoids significantly
repressed ARX expression (fig. S20, A and B).
Furthermore, as expected, the EEC differentia-
tion tr a je c tor y i n Z N F800
−/−
;PAX4
−/−
organoids
was redirected to an EC-biased phenotype upon
PA X4 reexpression.
Reciprocal transcriptional repression exists
between Pax4 and Arx during mouse pancrea-
tic development (46, 47). We assessed whether
ARX also inhibits intestinal PAX4 expression
by overexpressing ARX in ZNF800
−/−
organoids
(fig. S21A). ARX overexpression was insuffi-
cient to reverse the EC-biased EEC cell type
specification induced by the ZNF800-PAX4
axis (fig. S21, B and C). Furthermore, PAX4
expression was not affected upon ARX over-
expression in the ZNF800
−/−
condition (fig. S21D).
W e next performed ChIP-qPCR of ARX on the
PAX4 locus using FLAG-tagged ARX in human
SI organoids (fig. S21E). Unlike ZNF800, ARX
did not bind to the PAX4 upstream enhancer
region(fig.S21F).WealsoperformedChIP-qPCR
of PAX4 on the ARX locus using FLAG-tagged
PAX4 (fig. S22A), focusing on six ultraconserved
enhancers (48–50) (fig . S22B). PAX4 did not
bind across these enhancers, including hs121,
which exh ibits PAX4 binding activity in the
mouse pancreas (fig. S22C) (49). Overall, our
results strongly supported that PAX4 unilater-
ally inhibits ARX, whereas the inhibitory effect
does not involve direct chromatin interaction
through the previously described regulatory
elements.
Discussion
The human SI epithelium consists of at least
14 main cell types, including six EEC lineages
(51, 52). Leveraging the near-physio logical cell
heterogeneity of human SI organoids, we per-
formed a CRISPR screen for positive and neg-
ative TF regulators of EEC lineage commitment.
Our findings defin e a ZNF800 -repressive
mechanism upstream of the classic endocrine
gene regulatory network (Fig. 4E). Among its
direct downstream targets, INSM1, SOX4,and
NEUROG3 are well described central players
that drive early EEC commitment. We also
found that PAX4, in the absence of ZNF800,
drives an EC-specific cell fate by suppressing
differentiation of all other EEC subtypes.
The PAX4 knockout rescued somatostatin-
producing D cells in ZNF800
−/−
organoids
(Fig. 2D and fig. S7A). Although Pax4 con-
trols both b- and somatostatin-producing d-cell
specification in the mouse pancreas (46), our
single PAX4 knockout had no effect on SST-
expressing D cells (fig. S18C). This prompts
questions into the generalizability of endo-
crine fate regulation between different diges-
tive organs. Double depletion of Pax4 and Arx
promoted d-cell specification in mice (49),
suggesting that a third TF is involved in d-cell
cell differentiation, and that Pax4 is likely to in-
duce a b-cell fate at the expense of d cells. There-
fore, the up-regulation of PAX4 by ZNF800
−/−
in human SI organoids might drive a further
binary cell–fate decision between ECs and
D cells.
ZNF800 is ubiquitously expressed along the
crypt-villus axis in the adult human gut epi-
thelium (fig. S4A), marked by H3K4me3 en-
richment and low H3K27me3 levels (fig. S4B),
indicating an open chromatin state and active
expression. The scRNA-seq dataset of the devel-
oping human gut revealed that ZNF800 is
already expressed at the earliest assayed time
point of 6.1 postconception weeks (53). Given
the downstream TF network described in our
study, it appears likely that ZNF800 also plays
an important function in embryonic develop-
ment. A recent coexpression network study in
mouse pancreatic development (54) revealed
that expres sion of the mouse ortholog zfp800
correlates with endocrine specification from
embryonic day 8 (E8) until E15.5. Global knock-
out of zfp800 caused postnatal lethality and
disrupted early pancreatic development (in-
cluding both endocrine and acinar cells at
E18.5). Thus, the constitutive null phenotype
hindered a mechanistic study of mouse zfp800
function in the endocrine lineages. It is con-
ceivable that ZNF800 might regulate b-cell
differentiation in the human pancreas through
the TF network described in this study.
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AC KN OW LE D GM E NT S
We thank R. Sherwood (Harvard Medical School, Brigham and
Women's Hospital, Division of Genetics) for providing the TFome
sgRNA library in the CRISPR-v2-FE backbone. We thank D. Krueger,
A. de Graaff, and the Hubrecht Imaging Centre for microscopy
assistance and the Hubrecht Flow Cytometry Core Facility for flow
cytometry analysis and cell sorting. We thank the Máxima Single
Cell Genomics Facility and Utrecht Sequencing Facility for
sequencing support. We thank the Microscopy CORE Lab of
the Faculty of Health, Medicine, and Life Sciences of Maastricht
University for its help in transmission electron microscopy
imaging. We thank the ENCODE Consortium and the
ENCODE production laboratories (B. Bernstein, Broad;
J. Stamatoyannopoulos, UW; B. Ren, UCSD) for generating the
related ChIP-seq public datasets. Funding: This work was
supported by the Netherlands Organ-on-Chip Initiative, a Dutch
Research Council (NWO) Gravitation project (024.003.001) funded
by the Ministry of Education, Culture, and Science of the
government of the Netherlands (H.C.); the Oncode Institute (partly
financed by the Dutch Cancer Society) (H.C. and J.H.v.E.); and the
European Research Council under ERC advanced grant no.
101020405 (GutHormones) (H.C.). The project Organoids in time
with project no. 2019.085 of the research program NWO
Investment Large is financed by the NWO (H.C. S.v.d.B.). Author
contributions: Conceptualization: L.L. and H.C.; Methodology: L.L.,
J.De., D.W., G.J.F.v.S., R.v.d.L., H.B., J.K., S.v.d.B., A.A.-R., C.L.-I.,
W.J.v .d.W., A.B., T.M., M.v.d.W., P.J.P., J.Dr ., J.H.v.E., and H.C.; Investigation:
L.L., J.De., G.J.F.v.S., H.B., J.K., A.A.-R., C.L.-I., and W.J.v.d.W.;
Visualization: L.L., J.De., G.J.F.v.S., and C.L.-I.; Funding acquisition:
J.H.v. E. and H.C.; Project administration: J.H.v. E. and H.C.; Supervision:
J.H.v.E. and H.C.; Writing – original draft: L.L. and H.C.; Writing –
review and editing: all authors. Competing interests: H.C. is an
inventor on patents held by the Royal Netherlands Academy of Arts
and Sciences that cover organoid technology. He is currently
head of pharma Research and Early Development (pRED) at
RESEARCH | RESEARCH ARTICLE
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