Biology subjects

Lee, D. J.

Publications and source records attributed to Lee, D. J..

22 records · Page 2Linked to original sources

bioRxiv2021

Rapid redistribution and extensive binding of NANOG and GATA6 at shared regulatory elements underlie specification of divergent cell fates

Establishment of divergent cell types from a common progenitor requires transcription factors (TFs) to promote lineage-restricted transcriptional programs while suppressing alternative fates. In the mouse blastocyst, cells of the inner cell mass (ICM) coexpress NANOG and GATA6, two TFs that drive the bifurcation of these progenitors into either the epiblast (Epi) or the primitive endoderm (PrE), respectively. Here, using in vitro differentiation, we describe the molecular mechanisms of how GATA6 quickly induces the PrE fate while repressing the Epi lineage. GATA6 functions as a pioneer TF by inducing nucleosome repositioning at regulatory elements controlling PrE genes, making them accessible for deposition of active histone marks and leading to rewiring of chromatin interactions and ultimately transcriptional activation. GATA6 also binds most regulatory elements of Epi genes followed by eviction of the Epispecific TFs NANOG and SOX2, loss of active histone marks, and reduction in chromatin accessibility that culminates in transcriptional repression. Unexpectedly, evicted NANOG and SOX2 transiently bind PrE regulatory elements occupied by GATA6. Our study shows that GATA6 binds and modulate the same regulatory elements as Epi TFs, a phenomenon we also validated in blastocysts. We propose that the ability of PrE and Epi-specific TFs to extensively bind and regulate the same gene networks contributes to ICM plasticity and allows rapid cell lineage specification by coordinating both activation

developmental biology↗

bioRxiv2021

A counter-enzyme complex regulates glutamate metabolism in Bacillus subtilis

Multi-enzyme assemblies composed of metabolic enzymes catalyzing sequential reactions are being increasingly studied. Here, we report the discovery of a 1.6 megadalton multi-enzyme complex from Bacillus subtilis composed of two enzymes catalyzing opposite rather than sequential reactions ("counter-enzymes"): glutamate synthase (GltAB), and glutamate dehydrogenase (GudB), that make and break glutamate, respectively. In vivo and in vitro studies show that the primary role of complex formation is to inhibit GudBs activity as this enzyme is constitutively expressed including in glutamate-limiting conditions. Using cryo-electron microscopy, we elucidated the structure of the complex and the basis of GudBs inhibition. Finally, we show that this complex that exhibits unusual oscillatory progress curves is a necessity for planktonic growth in glutamate-limiting conditions, but is also essential for biofilm growth in glutamate-rich media, suggesting a regulatory role at fluctuating glutamate concentrations.

biochemistry↗

bioRxiv2021

Single cell chromatin accessibility reveals regulatory elements and developmental trajectories in the embryonic forebrain

A comprehensive characterization of epigemonic organization in the embryonic mouse forebrain will enhance our understanding of neurodevelopment and provide insight into mechanisms of neurological disease. We collected single-cell chromatin accessibility profiles from four distinct neurogenic regions of the embryonic mouse forebrain using single nuclei ATAC-Seq (snATAC-Seq). We identified thousands of differentially accessible peaks, many restricted to distinct progenitor cell types or brain regions. We integrated snATAC-Seq and single cell transcriptome data to characterize changes of chromatin accessibility at enhancers and promoters with associated transcript abundance. Multi-modal integration of histone modifications (CUT&Tag and CUT&RUN), promoter-enhancer interactions (Capture-C) and high-order chromatin structure (Hi-C) extended these initial observations. This dataset reveals a diverse chromatin landscape with region-specific regulatory mechanisms and genomic interactions in distinct neurogenic regions of the embryonic mouse brain and represents an extensive public resource of a ground truth epigenomic landscape at this critical stage of neurogenesis.

neuroscience↗

bioRxiv2019

Contributions to human breast milk microbiome and enteromammary transfer of Bifidobacterium breve

Increasing evidence supports the importance of the breast milk microbiome in seeding the infant gut. However, the origin of bacteria in milk and the process of milk microbe-mediated seeding of infant intestine need further elucidation. Presumed sources of bacteria in milk include locations of mother-infant and mother-environment interactions. We investigate the role of mother-infant interaction on breast milk microbes. Shotgun metagenomics and 16S rRNA gene sequencing identified milk microbes of mother-infant pairs in breastfed infants and in infants that have never latched. Although breast milk has low overall biomass, milk microbes play an important role in seeding the infant gut. Breast milk bacteria were largely comprised of Staphylococcus, Streptococcus, Acinetobacter, and Enterobacter primarily derived from maternal areolar skin and infant oral sites in breastfeeding pairs. This suggests that the process of breastfeeding is a potentially important mechanism for propagation of breast milk microbes through retrograde flux via infant oral and areolar skin contact. In one infant delivered via Caesarian section, a distinct strain of Bifidobacteria breve was identified in maternal rectum, breast milk and the infants stool potentially suggesting direct transmission. This may support the existence of microbial translocation of this anaerobic bacteria via the enteromammary pathway in humans, where maternal bacteria translocate across the maternal gut and are transferred to the mammary glands. Modulating sources of human milk microbiome seeding potentially imply opportunities to ultimately influence the development of the infant microbiome and health.

microbiology↗