Biology subjects

Radha, V.

Publications and source records attributed to Radha, V..

6 recordsLinked to original sources

bioRxiv2024

Developmental functions of rapgef1b in neural crest specification and presomitic mesoderm patterning

RAPGEF1, a guanine nucleotide exchange factor, regulates signaling and cytoskeletal dynamics in mammalian cells, yet its role in development remains unclear as Rapgef1 null mouse embryos do not survive beyond implantation. We demonstrate that zebrafish rapgef1 is maternally expressed, and its paralogs, rapgef1a and rapgef1b, exhibit tissue and developmental stage-specific splicing. Disruption of rapgef1b caused brain and somite defects, impaired cranial neural crest specification, and microcephaly-like phenotypes, uncovering its previously uncharacterized functions in morphogenesis and tissue patterning. Transcriptomic analyses and differential gene expression provide fresh insights into the developmental functions of rapgef1b in presomitic mesoderm and somitogenesis by modulating the Wnt/{beta} catenin signaling. Rapgef1b deficient embryos also showed spindle pole disorganization and chromosome mis-congression, linking Rapgef1 to centrosome-mediated mitotic fidelity. Together, our findings identify Rapgef1b as a key regulator of neural crest development, mesodermal morphogenesis, and early mitoses, highlighting its tissue-specific functions during vertebrate embryogenesis. TeaserIn this study, we show that rapgef1b is essential for shaping the embryonic brain, somites, and body axis by regulating gene expression, cell division, survival, and differentiation. Our findings reveal a new dimension of signaling-mediated cell fate specification during early vertebrate development.

developmental biology↗

bioRxiv2024

Development and tissue specific expression of RAPGEF1 (C3G) transcripts having exons encoding disordered segments with predicted regulatory function.

The ubiquitously expressed RAPGEF1(C3G), regulates differentiation, and is essential for development of mouse embryos. While multiple transcripts have been predicted, evidence of their expression and function is scarce. We demonstrate tissue and development specific expression of novel transcripts with exons 12-14 in various combinations, in the mouse. These exons encode an intrinsically disordered serine-rich polypeptide, that undergoes phosphorylation. Isoform switching occurred during differentiation of myoblasts and mouse embryonic stem cells. In silico structure and docking studies indicated that the additional exons alter intra-molecular interactions keeping it in a closed confirmation, and interaction with its target, RAP1A. Our results demonstrate the expression of novel RAPGEF1 isoforms, and suggest cassette exon inclusion as an additional means of regulating RAPGEF1 activity during differentiation.

molecular biology↗

bioRxiv2020

South Asian patient population genetics reveal strong founder effects and high rates of homozygosity - new resources for precision medicine

Population-scale genetic studies can identify drug targets and allow disease risk to be predicted with resulting benefit for management of individual health risks and system-wide allocation of health care delivery resources. Although population-scale projects are underway in many parts of the world, genetic variation between population groups means that additional projects are warranted. South Asia has a population whose genetics is the least characterized of any of the worlds major populations. Here we describe GenomeAsia studies that characterize population structure in South Asia and that create tools for economical and accurate genotyping at population-scale. Prior work on population structure characterized isolated population groups, the relevance of which to large-scale studies of disease genetics is unclear. For our studies we used whole genome sequence information from 4,807 individuals recruited in the health care delivery systems of Pakistan, India and Bangladesh to ensure relevance to population-scale studies of disease genetics. We combined this with WGS data from 927 individuals from isolated South Asian population groups, and developed a custom SNP array (called SARGAM) that is optimized for future human genetic studies in South Asia. We find evidence for high rates of reproductive isolation, endogamy and consanguinity that vary across the subcontinent and that lead to levels of homozygosity that approach 100 times that seen in outbred populations. We describe founder effects that increase the power to associate functional variants with disease processes and that make South Asia a uniquely powerful place for population-scale genetic studies.

genomics↗

bioRxiv2019

HSC70 regulates cold-induced caspase-1 hyperactivation by an autoinflammation-causing mutant of cytoplasmic immune receptor NLRC4

NLRC4 is an innate immune receptor, which upon detection of certain pathogens or internal distress signal, initiates caspase-1 mediated inflammatory response. A gain-of-function mutation, H443P in NLRC4, causes familial cold autoinflammatory syndrome (FCAS) characterized by cold-induced hyperactivation of caspase-1 and inflammation. Here, we show that heat shock cognate protein 70 (HSC70) complexes with NLRC4 and negatively regulates caspase-1 activation by NLRC4-H443P. Compared to NLRC4, the structurally altered NLRC4-H443P shows enhanced interaction with HSC70. Knockdown of HSC70 or inhibition of its ATPase activity enhances caspase-1 activation by NLRC4-H443P. Exposure to subnormal temperature resulted in reduced interaction of NLRC4-H443P with HSC70, and an increase in its ability to form ASC-specks and activate caspase-1. By demonstrating that HSC70 differentially interacts with NLRC4-H443P mutant in a temperature-dependent manner to regulate caspase-1 activation, we provide a mechanism for cold-induced inflammation seen in FCAS patients with NLRC4-H443P mutation.

cell biology↗

bioRxiv2019

C3G (RapGEF1) localizes to the mother centriole and regulates centriole division and primary cilia dynamics

C3G (RapGEF1), a negative regulator of {beta}-catenin, plays a role in cell differentiation and is essential for early embryonic development in mice. In this study, we identify C3G as a centrosomal protein that regulates centriole division and primary cilia dynamics. C3G is present at the centrosome in interphase as well as mitotic cells, but is absent at the centrioles in differentiated myotubes. It interacts with, and co-localizes with cenexin in the mother centriole. Stable clone of cells depleted of C3G by CRISPR/Cas9 showed reduction in cenexin protein, and presence of supernumerary centrioles. Over-expression of C3G resulted in inhibition of centrosome division in normal and hydroxyurea treated cells. Proportion of ciliated cells is higher, and cilia length longer in C3G knockout cells. C3G inhibits cilia formation and length dependent on its catalytic activity. Unlike wild type cells, C3G depleted cells inefficiently retracted their cilia upon stimulation to reenter the cell cycle, and proliferated slowly, arresting in G1. We conclude that C3G inhibits centriole division and maintains ciliary homeostasis, properties that may be important for its role in embryonic development.\n\nSummary statementWe identify C3G as a centrosomal protein and regulator of centriole number, primary cilia length and resorption. These properties are important for its role in embryogenesis, and suggest that mutations in C3G could cause ciliopathies.

cell biology↗

bioRxiv2017

C3G dynamically associates with Nuclear speckles and regulates mRNA splicing

C3G (RapGEF1), essential for mammalian embryonic development, is ubiquitously expressed and undergoes regulated nucleo-cytoplasmic exchange. Here we show that C3G localizes to SC35 positive nuclear speckles, and regulates splicing activity. Reversible association of C3G with speckles was seen upon inhibition of transcription and splicing. C3G shows partial colocalization with SC35, and is recruited to a chromatin and RNase sensitive fraction of speckles. Its presence in speckles is dependent on intact cellular actin cytoskeleton, and is lost upon expression of the kinase, Clk1. Rap1, a substrate of C3G, is also present in nuclear speckles and inactivation of Rap signalling by expression of GFP- Rap1GAP, alters speckle morphology and number. Enhanced association of C3G with speckles is seen upon GSK3{beta} inhibition, or differentiation of C2C12 cells to myotubes. CRISPR/Cas9 mediated knockdown of C3G resulted in decreased splicing activity and reduced staining for SC35 in speckles. C3G knockout clones of C2C12 as well as MDA-MB- 231 showed reduced protein levels of several splicing factors compared to control cells. Our results identify C3G and Rap1 as novel components of nuclear speckles and a role for C3G in regulating cellular RNA splicing activity.\n\nSummaryNuclear speckles are sites for pre-mRNA splicing. We provide evidence for localization and function of a Ras family GTPase, Rap1 and its exchange factor C3G in nuclear speckles.

cell biology↗