Biology subjects

Chan, S.-W.

Publications and source records attributed to Chan, S.-W..

4 recordsLinked to original sources

bioRxiv2025

Human Organoids Reveal PTEN-driven Mesendoderm Specification via Retinoic Acid Signaling Suppression

During early embryogenesis, epiblast cells ingress through the primitive streak (PS) and commit to a mesendoderm (MES) fate, giving rise to both mesodermal and endodermal lineages. Despite advancements in human organoid technology for modeling pre-implantation blastocyst stage, robust systems that accurately recapitulate MES specification and PS formation during the post-implantation stage remain limited. Here, we show that human induced pluripotent stem cells can be used to generate three-dimensional MES organoids that faithfully mimic in vivo human MES specification, particularly from the anterior PS. We demonstrate that MES organoid formation is dependent on PTEN expression and that loss of PTEN severely impairs the formation of mesoderm and definitive endoderm derivatives arising from MES organoids. To elucidate the molecular mechanisms underlying these defects, we conducted an integrative multi-omics analysis, including transcriptome, chromatin accessibility profiling, metabolism, and phosphoproteomics, on wild-type and PTEN-/-MES cells. These analyses revealed that PTEN suppresses retinoic acid (RA) signaling during MES lineage commitment. Furthermore, we identified the RA-degrading enzyme CYP26A1 as a downstream effector of PTEN. Notably, while excessive RA induced by PTEN ablation is detrimental to MES cell generation, physiological levels of RA are necessary. Collectively, our human MES organoids offer a valuable model for dissecting early human development, and our findings identify PTEN as a key regulator of MES fate commitment through inhibition of RA signaling.

developmental biology↗

bioRxiv2025

Primate-specific microRNA-1202 regulates dopaminergic neurogenesis by targeting APC2 and modulates WNT/β-catenin signaling pathway in midbrain organoid

MicroRNAs (miRNAs) are generally evolutionarily conserved, but a small number of them are found exclusively in primates. MiR-1202 is a primate-specific miRNA that was previously revealed as being involved in major depression disorder (MDD). Moreover, the genomic locus where miR-1202 locates (6q25.3) is strongly associated with recurrent early-onset MDD and neurodevelopmental disorder. We hypothesize that miR-1202 plays a unique role in the brain in fine-tuning the transcriptional network that governs neurogenesis. Here, we reported that microdeletion of miR-1202 resulted in retarded organoid growth but enhanced dopaminergic (DA) neuron differentiation in midbrain organoids. Integrated analysis of miRNA-interacting targets and transcriptional changes in miR-1202 knockout cells revealed that APC2, a negative regulator of canonical WNT/{beta}-catenin pathway, was a downstream target of miR-1202. Knockdown of APC2 resulted in attenuated DA neurogenesis, in contrast to the enhanced DA neurogenesis in miR-1202 knockout cells. Treatments of the brain organoids with antidepressants increased miR-1202 expression and simultaneously inhibited APC2 expression. Consistently, APC2 expression was found to increase in MDD patients. Our results suggest that miR-1202 regulates dopamine neurogenesis by inhibiting the APC2/WNT signaling pathway, which plays a distinct role in the midbrain-hindbrain regional patterning during the early development of the central nervous system.

cell biology↗

bioRxiv2021

Kite-shaped molecules block SARS-CoV-2 cell entry at a post-attachment step

Anti-viral small molecules are currently lacking for treating coronavirus infection. The long development timescales for such drugs are a major problem, but could be shortened by repurposing existing drugs. We therefore screened a small library of FDA-approved compounds for potential severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) antivirals using a pseudovirus system that allows a sensitive read-out of infectivity. A group of structurally-related compounds, showing moderate inhibitory activity with IC50 values in the 1-5{micro}M range, were identified. Further studies demonstrated that these kite-shaped molecules were surprisingly specific for SARS-CoV and SARS-CoV-2 and that they acted early in the entry steps of the viral infectious cycle, but did not affect virus attachment to the cells. Moreover the compounds were able to prevent infection in both kidney- and lung-derived human cell lines. The structural homology of the hits allowed the production of a well-defined pharmacophore that was found to be highly accurate in predicting the anti-viral activity of the compounds in the screen. We discuss the prospects of repurposing these existing drugs for treating current and future coronavirus outbreaks.

microbiology↗

bioRxiv2020

An unusual MHC molecule generates protective CD8+ T cell responses to chronic infection

The CD8+ T cell response to the intracellular parasite Toxoplasma gondii varies dramatically between mouse strains, resulting in differences in control of the parasite. Protection in BALB/c mice can be attributed to an unusually strong and protective MHC-1 Ld-restricted CD8+ T cell response directed against a peptide derived from the parasite antigen GRA6. The MHC-1 Ld molecule has limited peptide binding compared to conventional MHC molecules such as Kb or Db, which correlates with polymorphisms associated with "elite control" of HIV in humans. To investigate the link between the unusual MHC-1 molecule Ld and the generation of "elite controller" CD8+ T cell responses, we compared the GRA6-Ld specific T cell response to the well-studied OVA-Kb specific response, and demonstrated that GRA6-Ld specific T cells are significantly more protective and resistant to exhaustion in chronic T. gondii infection. To further investigate the connection between limited peptide presentation and robust T cell responses, we used CRISPR/Cas9 to generate mice with a point mutation (W97R) in the peptide-binding groove of Ld that results in broader peptide binding. We investigated the effect of this Ld W97R mutation on another robust Ld-restricted response against the IE1 peptide during Murine Cytomegalovirus (MCMV) infection. This mutation leads to an increase in exhaustion markers in the IE1-Ld specific CD8+ T cell response. Our results indicate that limited peptide binding by MHC-1 Ld correlates with the development of robust and protective CD8+ T cell responses that may avoid exhaustion during chronic infection.

immunology↗