Biology subjects

Narasimhan, M.

Publications and source records attributed to Narasimhan, M..

5 recordsLinked to original sources

bioRxiv2025

Integration of auxin and cytokinin signalling in Arabidopsis root meristem maintenance through the secreted peptide CLE40

Plant meristems perpetually generate new cells for the initiation, growth and differentiation of various cell types and organs. CLAVATA3/EMBRYO SURROUNDING REGION-RELATED (CLE) genes encode plant specific peptides exerting indispensable functions in a multitude of these developmental processes. Previously, we have described a CLE40 signaling module that regulates stemness in the distal root meristem (DRM). Here, we show that CLE40 is additionally needed to maintain the proximal root meristem (PRM). We demonstrate that in cle40 mutants, meristematic cells differentiate prematurely, resulting in shortened PRMs and ultimately, reduced root growth. Furthermore, we link these effects to increased cytokinin signaling that can be circumvented by preventing the perception of cytokinin. We highlight how increased cytokinin signaling leads to a change in auxin distribution mediated by SHORT HYPOCOTYL 2 (SHY2), which is ectopically activated if CLE40 is not active. Finally, we propose that the receptor BARELY ANY MERISTEM 1 (BAM1), but not its homolog BAM2, perceives CLE40 in the PRM.

developmental biology↗

bioRxiv2024

Autism and Intellectual Disability-Associated MYT1L Mutation Alters Human Cortical Interneuron Differentiation, Maturation, and Physiology

MYT1L is a neuronal transcription factor highly expressed in the developing and adult brain. While pathogenic MYT1L mutation causes neurodevelopmental disorders, these have not been characterized in human models of neurodevelopment. Here, we defined the consequences of pathogenic MYT1L mutation in human pluripotent stem cell-derived cortical interneurons. During differentiation, mutation reduced MYT1L expression and increased progenitor cell cycle exit and neuronal differentiation and synapse-related gene expression, morphological complexity, and synaptic puncta formation. Conversely, interneuron maturation was compromised, while variant neurons exhibited altered sodium and potassium channel activity and reduced function in electrophysiological analyses. CRISPRi-based knockdown similarly impaired interneuron differentiation and maturation, supporting loss of function-based effects. We further defined MYT1L genome-wide occupancy in interneurons and related this to the transcriptomic dysregulation resulting from MYT1L mutation, to identify direct targets that could mediate these phenotypic consequences. Together, this work delineates contributors to the etiology of neurodevelopmental disorders resulting from MYT1L mutation.

developmental biology↗

bioRxiv2024

Macromolecular toolbox to elucidate CLE-RLK binding, signaling and downstream effects

Plant peptides communicate by binding to a large family of receptor-like kinases (RLKs) and they share a conserved binding mechanism, which may account for their promiscuous interaction with several RLKs. In order to understand the in vivo binding specificity of CLE peptide family, we have developed a novel set of CLAVATA 3 (CLV3) based peptide tools. After carefully evaluating the CLE peptide binding characteristics, using solid phase synthesis process, we have modified the CLV3 peptide and attached a fluorophore and a photoactivable side group. We observed that the labeled CLV3 shows binding specificity within CLAVATA1 clade of RLKs while avoiding the distantly-related PEP RECEPTOR clade, thus resolving the contradictory results obtained previously by many in vitro methods. Furthermore, we observed that the RLK-bound CLV3 undergoes clathrin-mediated endocytosis and gets trafficked to vacuole via ARA7-labeled endosomes. Additionally, modifying CLV3 for light-controlled activation enabled spatial and temporal control over CLE signalling. Hence our CLV3 macromolecular toolbox can be used to study rapid cell specific down-stream effects. Given the conserved binding properties, in the future our toolbox can also be used as a template to modify other CLE peptides. HighlightA macromolecular tool box consisting of modified CLE peptide with fluorescent molecule and photoactivable group offers reliable insights into its in vivo binding characteristics, localization and signaling.

cell biology↗

bioRxiv2022

SH3Ps recruit auxilin-like vesicle uncoating factors into clathrin-mediated endocytosis

Clathrin-mediated endocytosis (CME) is an essential process of cellular cargo uptake operating in all eukaryotes. In animal and yeast, CME involves BAR-SH3 domain proteins, endophilins and amphiphysins, which function at the conclusion of CME to recruit factors for vesicle scission and uncoating. Arabidopsis thaliana contains BAR-SH3 domain proteins SH3P1-3, but their role is poorly understood. We identify SH3P1-3 as functional homologues of endophilin/amphiphysin. SH3P1-3 bind to discrete foci at the plasma membrane (PM), and colocalization indicates late recruitment of SH3P2 to a subset of clathrin-coated pits. PM recruitment pattern of SH3P2 is nearly identical to its interactor, a putative vesicle uncoating factor AUXILIN-LIKE1, and SH3P1-3 are required for most of AUXILIN-LIKE1 PM binding. This indicates a plant-specific modification of CME, where BAR-SH3 proteins recruit auxilin-like uncoating factors, rather than the uncoating phosphatases synaptojanins. Furthermore, we identify an unexpected redundancy between SH3P1-3 and a plant-specific endocytic adaptor, TPLATE complex, showing a contribution of SH3P1-3 to gross CME.

plant biology↗

bioRxiv2019

Evolutionary unique mechanistic framework of clathrin-mediated endocytosis in plants

In plants, clathrin mediated endocytosis (CME) represents the major route for cargo internalisation from the cell surface. It has been assumed to operate in an evolutionary conserved manner as in yeast and animals. Here we report characterisation of ultrastructure, dynamics and mechanisms of plant CME as allowed by our advancement in electron microscopy and quantitative live imaging techniques. Arabidopsis CME follows the constant curvature model and the bona fide CME population generates vesicles of a predominantly hexagonal type; larger and with faster kinetics than in other models. Contrary to the existing paradigm, actin is dispensable for CME events at the surface but plays a unique role in collecting endocytic vesicles, sorting of internalised cargos and directional endosome movement that itself actively promote CME events. Internalized vesicles display a strongly delayed and sequential uncoating. These unique features highlight the independent evolution of the plant CME mechanism during the autonomous rise of multicellularity in eukaryotes.

plant biology↗