Biology subjects

Prajapati, R. S.

Publications and source records attributed to Prajapati, R. S..

3 recordsLinked to original sources

bioRxiv2021

The chromatin remodelling factor Chd7 protects auditory neurons and sensory hair cells from stress-induced degeneration

Neurons and sensory cells are particularly vulnerable to oxidative stress due to their high oxygen demand during stimulus perception and transmission1-4. The mechanisms that protect them from stress-induced death and degeneration remain elusive. Here we show that embryonic deletion of the chromodomain helicase DNA-binding protein 7 (CHD7) in auditory neurons or hair cells leads to sensorineural hearing loss due to postnatal degeneration of both cell types. Mechanistically, we demonstrate that CHD7 controls the expression of major stress pathway components. In its absence, hair cells are hypersensitive, dying rapidly after brief exposure to stress inducers, suggesting that sound at the onset of hearing triggers their degeneration. In humans, CHD7 haploinsufficiency causes CHARGE syndrome, a disorder affecting multiple organs including the ear5,6. Our findings suggest that CHD7 mutations cause developmentally silent phenotypes that predispose cells to postnatal degeneration due to a failure of protective mechanisms.

developmental biology↗

bioRxiv2019

Greb1 is required for axial elongation and segmentation in vertebrate embryos.

During vertebrate embryonic development, the formation of axial structures is driven by a population of stem-like cells that reside in a region of the tailbud called the chordoneural hinge (CNH). We have compared the CNH transcriptome with those of surrounding tissues and shown that the CNH and tailbud mesoderm are transcriptionally similar, and distinct from the presomitic mesoderm. Amongst CNH-enriched genes are several that are required for axial elongation, including Wnt3a, Cdx2, Brachyury/T and Fgf8, and androgen/estrogen receptor nuclear signalling components such as Greb1. We show that the pattern and duration of tailbud Greb1 expression is conserved in mouse, zebrafish, and chicken embryos, and that Greb1 is required for axial elongation and somitogenesis in zebrafish embryos. The axial truncation phenotype of Greb1 morphant embryos is explained by much reduced expression of No tail (Ntl/Brachyury) which is required for axial progenitor maintenance. Posterior segmentation defects in the morphants (including misexpression of genes such as mespb, myoD and papC) appear to result, in part, from lost expression of the segmentation clock gene, her7.

developmental biology↗

bioRxiv2019

PRDM1 controls the sequential activation of neural, neural crest and sensory progenitor determinants by regulating histone modification

During early embryogenesis, the ectoderm is rapidly subdivided into neural, neural crest and sensory progenitors. How the onset of lineage-specific determinants and the loss of pluripotency markers are temporally and spatially coordinated in vivo remains an open question. Here we identify a critical role for the transcription factor PRDM1 in the orderly transition from epiblast to defined neural lineages. Like pluripotency factors, PRDM1 is expressed in all epiblast cells prior to gastrulation, but lost as they begin to differentiate. We show that, unlike pluripotency factors, PRDM1 is initially required for the activation of neural, neural crest and sensory progenitor specifiers and for the downregulation of pluripotency-associated genes. In vivo chromatin immunoprecipitation reveals stage-specific binding of PRDM1 to regulatory regions of neural and sensory progenitor genes, PRDM1-dependent recruitment of the histone demethylase Kdm4a to these regions and associated removal of repressive histone marks. Once lineage determinants become expressed, they repress PRDM1, and our data suggest that PRDM1 downregulation is required for cells to maintain their identity. Thus, PRDM1 mediates chromatin modifications that directly control neural and sensory progenitor genes, and its activities switch from an activator at early stages to a repressor once neural fates have been established.

developmental biology↗