Category Archives: Publications

CTCF-organized Chromatin Structures Mediate the Spatio-temporal Propagation of Replication Foci

by Qian Peter Su*, Ziqing Winston Zhao*, Luming Meng, Miao Ding, Weiwei Zhang, Yongzheng Li, Mengzhu Liu, Rongqin Li, Yi-Qin Gao, Xiaoliang Sunney Xie, Yujie Sun

bioRxiv (2019) doi: https://doi.org/10.1101/525915

Mammalian DNA replication is initiated at numerous replication origins, which are clustered into thousands of replication domains (RDs) across the genome. However, it remains unclear whether
the replication origins within each RD are activated stochastically. To understand how replication is regulated at the sub-RD level, we directly visualized the spatio-temporal organization, morphology, and in situ epigenetic signatures of individual replication foci (RFi) across S-phase using super-resolution stochastic optical reconstruction microscopy (STORM). Importantly, we revealed a hierarchical radial pattern of RFi propagation that reverses its directionality from early to late S-phase, and is diminished upon caffeine treatment or CTCF knockdown. Together with simulation and bioinformatic analyses, our findings point to a ‘CTCF-organized REplication Propagation’ (CoREP) model. The CoREP model suggests a non-random selection mechanism for replication activation mediated by CTCF at the sub-RD level, as well as the critical involvement of local chromatin environment in regulating replication in space and time.

Structure of the thermally stable Zika virus

by Victor A. Kostyuchenko, Elisa X. Y. Lim, Shuijun Zhang, Guntur Fibriansah, Thiam-Seng Ng, Justin S. G. Ooi, Jian Shi & Shee-Mei Lok

Nature (2016) doi:10.1038/nature17994  Published online 19 April 2016

Zika virus (ZIKV), formerly a neglected pathogen, has recently been associated with microcephaly in fetuses1, and with Guillian–Barré syndrome in adults2. Here we present the 3.7 Å resolution cryo-electron microscopy structure of ZIKV, and show that the overall architecture of the virus is similar to that of other flaviviruses. Sequence and structural comparisons of the ZIKV envelope (E) protein with other flaviviruses show that parts of the E protein closely resemble the neurovirulent West Nile and Japanese encephalitis viruses, while others are similar to dengue virus (DENV). However, the contribution of the E protein to flavivirus pathobiology is currently not understood. The virus particle was observed to be structurally stable even when incubated at 40 °C, in sharp contrast to the less thermally stable DENV3. This is also reflected in the infectivity of ZIKV compared to DENV serotypes 2 and 4 (DENV2 and DENV4) at different temperatures. The cryo-electron microscopy structure shows a virus with a more compact surface. This structural stability of the virus may help it to survive in the harsh conditions of semen4, saliva5 and urine6. Antibodies or drugs that destabilize the structure may help to reduce the disease outcome or limit the spread of the virus.

Read online: Nature.

Transcriptional enhancement of Smn levels in motoneurons is crucial for proper axon morphology in zebrafish

by Zoltan Spiro, Angela Koh, Shermaine Tay, Kelvin See, Christoph Winkler

Scientific Reports 6, 2016  (07 June 2016)

An unresolved mystery in the field of spinal muscular atrophy (SMA) is why a reduction of the ubiquitously expressed Smn protein causes defects mostly in motoneurons. We addressed the possibility that this restricted vulnerability stems from elevated Smn expression in motoneurons. To explore this, we established an ex vivo zebrafish culture system of GFP-marked motoneurons to quantitatively measure Smn protein and smn mRNA levels as well as promoter activity in motoneurons versus other cell types. Importantly, we uncovered that Smn levels are elevated in motoneurons by means of transcriptional activation. In addition, we identified the ETS family transcription factor Etv5b to be responsible for increased smn transcription in motoneurons. Moreover, we established that the additional supply of Smn protein in motoneurons is necessary for proper axonogenesis in a cell-autonomous manner. These findings demonstrate the reliance of motoneurons on more Smn, thereby adding a novel piece of evidence for their increased vulnerability under SMA conditions.

Read online: Scientific Reports