particular symmetry of the MFI framework
gives it local flexibility and overall rigidity,
which allows subcell deformation to accom-
modate larger molecules but still maintain
the stability of the entire zeolite framework.
We termed this structural characteristic of the
MFI zeolite as subcell topological flexibility.
Summary
Combining iDPC-STEM imaging with an at-
mosphere system, we achieved in situ obser-
vation of the dynamic subcell topological
deformation of MFI channels with atomic
resolution while the whole MFI zeolite single-
crystal structure was maintained nearly un-
changed. We revealed the intrinsic mechanism
of a molecule breaking through the pore size
limit. Upon benzene adsorption, the straight
channels underwent severe local deformation
along the unified orientations of guest mole-
cules, which allowed the diffusion of larger
molecules.
This subcell topological flexibility mainly
comes from the soft Si-O-Si hinges between
rigid tetrahedral SiO 4 , verified in AIMD sim-
ulations and our experimental results. In the
in situ benzene desorption process, we cap-
tured the dynamic evolution of zeolite channels
with decreasing numbers of benzene mole-
cules, indicating that the degree of subcell
local deformation is positively correlated with
the shape and amount of confined benzene
molecules. Furthermore, the symmetry of the
MFI framework enables mutual compensation
by large deformation of adjacent channels,
thereby keeping the overall crystal structure
stable and resulting in macroscopically rigid
behavior. As a consequence, the MFI frame-
work is highly industrially applicable in the
family of zeolites. These results confirmed the
microscopic subcell topological flexibility of a
macroscopically rigid zeolite framework and
revealed its chemical nature, advancing our
understanding of the intrinsic mechanism of
molecular diffusion breaking through the pore
size limit and the impact of subcell topological
flexibility on adsorption and catalytic trans-
formation in microporous materials.
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ACKNOWLEDGMENTS
We thank F. Lu and B. Y. Shen for discussions, and Tsinghua
National Laboratory for Information Science and Technology for
assistance with the energy simulation.Funding:National Key
Research and Development Program of China grants
2020YFB0606401, 2018YFE0122600, 2018YFB0604801, and
2021YFA1502600; National Natural Science Foundation of China
grants 22005170, 22125304, and 22032005.Author
contributions:Conceptualization: F.W., X.C. Methodology: H.X.,
X.C., Z.L., H.W., Investigation: H.X., X.C., Z.L. Visualization: H.X.,
X.C., Z.L. Supervision: F.W., X.C., C.Z., A.Z. Writing–original draft:
H.X. Writing–review and editing: F.W., X.C., C.Z., H.X., W.Q., Z.L.,
A.Z.Competing interests:Authors declare that they have no
competing interests.Data and materials availability:All data
needed to evaluate the conclusions in the paper are present in the
paper and the supplementary materials.SUPPLEMENTARY MATERIALS
science.org/doi/10.1126/science.abn7667
Materials and Methods
Figs. S1 to S21
Table S1
Movie S1
Data S1 to S3
References ( 49 – 53 )
17 December 2021; accepted 16 February 2022
10.1126/science.abn7667REPORTS
◥DYNAMIC GENOMEDynamics of CTCF- and cohesin-mediated chromatin
looping revealed by live-cell imaging
Michele Gabriele1,2,3†, Hugo B. Brandão1,2,3†‡, Simon Grosse-Holz4,5†, Asmita Jha1,2,3,
Gina M. Dailey^6 , Claudia Cattoglio6,7, Tsung-Han S. Hsieh6,7, Leonid Mirny,4,5,8*,
Christoph Zechner9,10,11,12*, Anders S. Hansen1,2,3*Animal genomes are folded into loops and topologically associating domains (TADs) by CTCF and
loop-extruding cohesins, but the live dynamics of loop formation and stability remain unknown. Here,
we directly visualized chromatin looping at theFbn2TAD in mouse embryonic stem cells using
super-resolution live-cell imaging and quantified looping dynamics by Bayesian inference. Unexpectedly,
theFbn2loop was both rare and dynamic, with a looped fraction of approximately 3 to 6.5% and a
median loop lifetime of approximately 10 to 30 minutes. Our results establish that theFbn2TAD is
highly dynamic, and about 92% of the time, cohesin-extruded loops exist within the TAD without
bridging both CTCF boundaries. This suggests that single CTCF boundaries, rather than the fully
CTCF-CTCF looped state, may be the primary regulators of functional interactions.M
ammalian genomes are folded into
loops and domains known as topolog-
ically associating domains (TADs) by
the proteins CTCF and cohesin ( 1 ).
Mechanistically, cohesin is thought
to load on DNA and bidirectionally extrudeloops until it is blocked by CTCF such that
CTCF establishes TAD boundaries ( 2 – 6 ). Func-
tionally, CTCF- and cohesin-mediated looping
and TADs play critical roles in multiple nuclear
processes, including regulation of gene expres-
sion, somatic recombination, and DNA repair496 29 APRIL 2022•VOL 376 ISSUE 6592 science.orgSCIENCE
RESEARCH