Biology subjects

Raj, B.

Publications and source records attributed to Raj, B..

4 recordsLinked to original sources

bioRxiv2026

Single-cell chromatin profiling reveals dynamic regulatory logic and enhancer elements in brain and retina development

Cell type identity in the nervous system is encoded within cis-regulatory landscapes that integrate transcription factor activity with chromatin accessibility. However, how these regulatory programs are organized and remodeled during post-embryonic neural development is poorly understood. We generate a temporally resolved single-cell chromatin accessibility atlas of [~]95,000 zebrafish brain and retina nuclei spanning larval, juvenile, and adult stages. We define 212 discrete chromatin states and uncover widespread, cell type-specific chromatin reorganization across development. By integrating with transcriptomic data, we link motif accessibility to transcription factor expression and identify regulatory programs that are either maintained or reconfigured during post-embryonic development of each neural cell type. Leveraging this atlas, we systematically identify and functionally validate candidate enhancers in vivo. Focusing on the slc1a3b locus in radial glia, we define evolutionarily conserved, compact enhancer modules that act combinatorially to drive gene expression. Together, these findings provide a systems-level framework for decoding neural regulatory logic and enable functional dissection of conserved cis-regulatory programs in the vertebrate nervous system.

developmental biology↗

bioRxiv2024

Barcoding Notch signaling in the developing brain

Developmental signaling inputs are fundamental for shaping cell fates and behavior. However, traditional fluorescent-based signaling reporters have limitations in scalability and molecular resolution of cell types. We present SABER-seq, a CRISPR-Cas molecular recorder that stores transient developmental signaling cues as permanent mutations in cellular genomes for deconstruction at later stages via single-cell transcriptomics. We applied SABER-seq to record Notch signaling in developing zebrafish brains. SABER-seq has two components: a signaling sensor and a barcode recorder. The sensor activates Cas9 in a Notch-dependent manner with inducible control while the recorder accumulates mutations that represent Notch activity in founder cells. We combine SABER-seq with an expanded juvenile brain atlas to define cell types whose fates are determined downstream of Notch signaling. We identified examples wherein Notch signaling may have differential impact on terminal cell fates. SABER-seq is a novel platform for rapid, scalable and high-resolution mapping of signaling activity during development.

developmental biology↗

bioRxiv2019

Emergence of neuronal diversity during vertebrate brain development

Neurogenesis in the vertebrate brain comprises many steps ranging from the proliferation of progenitors to the differentiation and maturation of neurons. Although these processes are highly regulated, the landscape of transcriptional changes and progenitor identities underlying brain development are poorly characterized. Here, we describe the first developmental single-cell RNA-seq catalog of more than 200,000 zebrafish brain cells encompassing 12 stages from 12 hours post-fertilization to 15 days post-fertilization. We characterize known and novel gene markers for more than 800 clusters across these timepoints. Our results capture the temporal dynamics of multiple neurogenic waves from embryo to larva that expand neuronal diversity from [~]20 cell types at 12 hpf to [~]100 cell types at 15 dpf. We find that most embryonic neural progenitor states are transient and transcriptionally distinct from long-lasting neural progenitors of post-embryonic stages. Furthermore, we reconstruct cell specification trajectories for the retina and hypothalamus, and identify gene expression cascades and novel markers. Our analysis reveal that late-stage retinal neural progenitors transcriptionally overlap cell states observed in the embryo, while hypothalamic neural progenitors become progressively distinct with developmental time. These data provide the first comprehensive single-cell transcriptomic time course for vertebrate brain development and suggest distinct neurogenic regulatory paradigms between different stages and tissues.

developmental biology↗

bioRxiv2017

Simultaneous single-cell profiling of lineages and cell types in the vertebrate brain by scGESTALT

Hundreds of cell types are generated during development, but their lineage relationships are largely elusive. Here we report a technology, scGESTALT, which combines cell type identification by single-cell RNA sequencing with lineage recording by cumulative barcode editing. We sequenced ~60,000 transcriptomes from the juvenile zebrafish brain and identified more than 100 cell types and marker genes. We engineered an inducible system that combines early and late barcode editing and isolated thousands of single-cell transcriptomes and their associated barcodes. The large diversity of edited barcodes and cell types enabled the generation of lineage trees with hundreds of branches. Inspection of lineage trajectories identified restrictions at the level of cell types and brain regions and helped uncover gene expression cascades during differentiation. These results establish scGESTALT as a new and widely applicable tool to simultaneously characterize the molecular identities and lineage histories of thousands of cells during development and disease.

developmental biology↗