Biology subjects

Tam, P.

Publications and source records attributed to Tam, P..

8 recordsLinked to original sources

bioRxiv2025

DNA methylation reprogramming in marsupial embryos is restricted to the extraembryonic lineage

DNA methylation (5mC) is an epigenetic mark that plays a critical role in defining cell fate. Following fertilisation, DNA methylation inherited from gametes must be reprogrammed to establish totipotency and enable the parental-to-zygotic transition. To accomplish this, non-mammalian vertebrates such as zebrafish and medaka subtly reprogram maternal 5mC profiles while maintaining high methylation levels throughout embryogenesis. In contrast, eutherian mammals such as mouse and human undergo global 5mC erasure in both embryonic and extraembryonic lineages. However, while embryonic 5mC is rapidly re-established to high levels upon implantation, the trophectoderm, which gives rise to the placenta, displays sustained and conserved DNA hypomethylation, suggesting that this drastic 5mC erasure may be functionally linked to complex placentation in mammals. To clarify whether extensive post-fertilisation 5mC erasure co-evolved with placentation, we explored embryonic methylation dynamics in marsupials, a lineage of therian mammals with a short-lived placenta. We produced a near complete telomere-to-telomere (T2T) genome and generated detailed epigenome maps of embryonic development for an Australian marsupial, the fat-tailed dunnart (Sminthopsis crassicaudata). We found the dunnart embryo exhibits genome wide DNA demethylation at the blastocyst stage, but these changes occur in the trophectoderm only, suggesting that 5mC erasure in the placenta is an ancestral state in therian mammals. Furthermore, the T2T-level dunnart genome assembly enabled identification of sex chromosomes, uncovering extensive hypomethylation of the paternally-inherited inactive X chromosome in females and revealing the previously unannotated master regulator of X chromosome inactivation, lncRNA Rsx. Our data indicate that while the use of genome-wide 5mC erasure differs between eutherian and marsupial lineages, 5mC erasure in extraembryonic tissue is ancestral to therian mammals and may be necessary to support placental development. HIGHLIGHTSO_LIFirst embryonic DNA methylation maps in an Australian marsupial C_LIO_LIExtensive global erasure of DNA methylation in the trophectoderm C_LIO_LIMaintenance of high DNA methylation in the embryonic lineage C_LIO_LIHypomethylated paternal X chromosome with methylated escapee genes C_LI

developmental biology↗

bioRxiv2025

Refate identifies chemical compounds to target trans-regulatory networks for cellular conversion

Identifying chemical compounds that target trans-regulatory networks (TRNs) underlying molecular programs of cells for directed cellular conversion (i.e. differentiation, reprogramming, transdifferentiation, and dedifferentiation) is a key step towards advancing regenerative medicine. Recent innovations in single-cell omics technologies enabled high-resolution profiling of TRNs that govern cell identity and cell-fate decisions. Here, we introduce Refate, a computational framework that integrates large-scale multimodal single-cell atlas data to quantify cell propensity of genes, together with six drug databases, to identify chemical compounds that target TRNs for directed cellular conversion. The reconstructed TRNs, including protein-protein interactions and gene regulatory networks, alongside chemical compounds that drive the cellular conversion provide greater biological interpretability and improve efficiency and efficacy. We evaluated Refate by testing its ability to uncover known transcription factors and chemical compounds validated in experimental conversions of various cell types. Furthermore, we experimentally validated the attribute of several novel chemical compounds identified by Refate for enhancing the conversion of human embryonic stem cells to human cranial neural crest cells. Together, these findings demonstrate Refate as an effective tool for discovering chemical compounds that target TRNs to enable cellular conversion, advancing efforts towards regenerative medicine. HighlightsO_LIRefate quantifies genes for cellular conversion using multimodal single-cell atlases C_LIO_LIRefate uncovers trans-regulatory networks (TRNs) underlying cellular conversion C_LIO_LIRefate identifies chemical compounds that target TRNs for cellular conversion C_LIO_LIValidation of Refate identified chemical compounds for hESC to hCNCC conversion C_LI

developmental biology↗

bioRxiv2024

Spatiotemporal Regulatory Logics of Mouse Gastrulation

Spatiotemporal coordination of cellular and molecular events is crucial for cell fate commitment during mouse gastrulation. However, the high-precision mechanisms governing the timing and spatial dynamics remain poorly understood. Here, we present a time-series single-cell multi-omic dataset from the mouse gastrulating embryos and construct a hierarchical gene regulatory landscape. Integrating this with real three-dimensional transcriptomic coordinate, we created ST-MAGIC and ST-MAGIC (+) atlas, dissecting the spatiotemporal logics of regulatory networks and signaling responsiveness underpinning the lineage commitment at gastrulation. Specifically, we delineated the multi-omic basis for left-right symmetry breaking events in the gastrula and also revealed the spatiotemporal molecular relay for axial mesendoderm lineage, where early and intermediate transcription factors first open the chromatin regions and setup the responsiveness to signaling, followed by terminal factors to consolidate the transcriptomic architecture. In summary, our study presents a spatiotemporal regulatory logic framework of mouse gastrulation, that advances our understanding of mammalian embryogenesis.

developmental biology↗

bioRxiv2023

Time, Space and Single-Cell Resolved Molecular Trajectory of Cell Populations and the Laterality of the Body Plan at Gastrulation

Understanding of the molecular drivers of lineage diversification and tissue patterning during primary germ layer development requires in-depth knowledge of the dynamic molecular trajectories of cell lineages across a series of developmental stages of gastrulation1-7. Through computational modeling, we constructed at single-cell resolution a spatio-temporal compendium of the molecular trajectories of germ-layer derivatives in gastrula-stage mouse embryos. This molecular atlas infers the developmental trajectories of single-cell populations and the molecular network activity underpinning the specification and differentiation of the germ-layer lineages. Analysis of the heterogeneity of cellular composition of cell populations at defined positions in the epiblast revealed progressive diversification of cell types, mirroring the process of lineage allocation during gastrulation. A novel observation is the difference in the contribution of cells on contralateral sides of the epiblast to mesoderm derivatives of the early organogenesis embryo, and the enhanced BMP signaling activity in right-side mesoderm of E7.5 embryo. Perturbation of BMP signaling activity at late gastrulation led to randomization of left-right (L-R) molecular asymmetry in the lateral mesoderm of early-somite-stage embryo. Our findings indicate the asymmetric BMP activity during gastrulation may be critical for the symmetry breaking process associated with specification of L-R body asymmetry ahead of the acquisition of functionality of the L-R organizer.

developmental biology↗

bioRxiv2023

LoxCode in vivo clonal barcoding resolves mammalian epiblast contribution to fetal organs

Much remains to be learned about the clonal fate of mammalian epiblast cells in vivo. Here we develop a high diversity, high throughput, Cre recombinase-driven DNA LoxCode barcoding technology for in vivo clonal lineage tracing. E5.5 pre-gastrulation embryos were barcoded in utero and epiblast clones later assessed for their contribution to a wide range of tissues and cell types in the E12.5 organogenesis-stage embryo. While a few epiblast clones contributed broadly to most tissues and cell types of the three germ layers, many clones were lineage biased towards either blood, ectoderm lineages, mesenchymal tissues or limbs. In addition to lineage bias, most epiblast clones were differentially fated for tissue types or descendants in tissues compartments across the body axes. Using a stochastic agent-based model of embryogenesis and LoxCode barcoding, we inferred and experimentally validated predicted cell fate biases as well as clonal compositions across tissues that are consistent with events of lineage segregation and shared trajectory of lineage differentiation. Our study has demonstrated the power of LoxCode barcoding in investigating multi-modal clonal fate at high throughput, thus enabling an in-depth interrogation of the clonal contribution of E5.5 epiblast cells to fetal tissues, organs and body parts.

developmental biology↗

bioRxiv2020

Deviation from baseline mutation burden provides powerful and robust rare-variants association test for complex diseases

The identification of rare variants that contribute to complex diseases is challenging due to low statistical power. Here we propose a novel and powerful rare variants association test based on the deviation of the observed mutational burden in a genomic region from a baseline mutation burden predicted by weighted recursive truncated negative-binomial regression (RUNNER) on genomic features available from public data. Simulation studies show that RUNNER is substantially more powerful than state-of-the-art rare variant association methods (including SKAT, CMC and KBAC), while maintaining correct type 1 error rates under population stratification and in small samples. Applied to real data, RUNNER “rediscovered” known genes of Hirschsprung disease missed by current methods, and detected promising new candidate genes, including NXPE4 for Hirschsprung disease and CXCL16 for Alzheimer’s disease. The proposed approach provides a powerful and robust method to identify rare risk variants for complex diseases.Competing Interest StatementThe authors have declared no competing interest.View Full Text

genetics↗

bioRxiv2019

Comparative analysis of diverse cell states establishes an epigenetic basis for inferring regulatory genes governing cell identity

Determining genes orchestrating cell differentiation in development and disease remains a fundamental goal of cell biology. This study establishes a genome-wide metric based on the gene-repressive tri-methylation of histone 3 lysine 27 (H3K27me3) across hundreds of diverse cell types to identify genetic regulators of cell differentiation. We introduce a computational method, TRIAGE, that uses discordance between gene-repressive tendency and expression to identify genetic drivers of cell identity. We apply TRIAGE to millions of genome-wide single-cell transcriptomes, diverse omics platforms, and eukaryotic cells and tissue types. Using a wide range of data, we validate TRIAGEs performance for identifying cell-type specific regulatory factors across diverse species including human, mouse, boar, bird, fish, and tunicate. Using CRISPR gene editing, we use TRIAGE to experimentally validate RNF220 as a regulator of Ciona cardiopharyngeal development and SIX3 as required for differentiation of endoderm in human pluripotent stem cells. A record of this papers Transparent Peer Review process is included in the Supplemental Information.

cell biology↗

bioRxiv2017

Cardiac directed differentiation using small molecule Wnt modulation at single-cell resolution

Differentiation into diverse cell lineages requires the orchestration of gene regulatory networks guiding diverse cell fate choices. Utilizing human pluripotent stem cells, we measured expression dynamics of 17,718 genes from 43,168 cells across five time points over a thirty day time-course of in vitro cardiac-directed differentiation. Unsupervised clustering and lineage prediction algorithms were used to map fate choices and transcriptional networks underlying cardiac differentiation. We leveraged this resource to identify strategies for controlling in vitro differentiation as it occurs in vivo. HOPX, a non-DNA binding homeodomain protein essential for heart development in vivo was identified as dys-regulated in in vitro derived cardiomyocytes. Utilizing genetic gain and loss of function approaches, we dissect the transcriptional complexity of the HOPX locus and identify the requirement of hypertrophic signaling for HOPX transcription in hPSC-derived cardiomyocytes. This work provides a single cell dissection of the transcriptional landscape of cardiac differentiation for broad applications of stem cells in cardiovascular biology.

developmental biology↗