Biology subjects

Akella, J. S.

Publications and source records attributed to Akella, J. S..

5 recordsLinked to original sources

bioRxiv2023

Cell-specific alpha-tubulin TBA-6 and pan-ciliary IFT cargo RAB-28 generate a non-canonical transition zone

The transition zone (TZ) regulates cilia composition and function. Canonical TZs with 9 doublet microtubules (MTs) are common but non-canonical TZs that vary from 9 MT symmetry also occur and arise through unknown mechanisms. Cilia on the quadrant inner labial type 2 (IL2Q) neurons of C. elegans have a specialized non-canonical TZ with fewer than 9 doublet MTs. We previously showed that non-canonical TZs in IL2Q cilia arise via MT loss and reorganization of canonical TZs. Here, we identify structural events and mechanisms that generate non-canonical TZs. Cell-specific -tubulin TBA-6 and pan-ciliary IFT cargo RAB-28 regulate IL2QTZ MT loss without affecting ciliary assembly. Our results reveal a role for the tubulin code in generating non-canonical TZs and contribute towards understanding ciliary functional specialization. Author summaryCiliary microtubules are exquisitely diverse in arrangements and composition. Studies on how ciliary ultrastructural diversity is generated are essential to our understanding of cilia function in diverse healthy and pathological contexts. Despite its clinical relevance, the ultrastructural diversity of the transition zone and its microtubules remains understudied. Here, we uncover mechanisms contributing to generating ultrastructural diversity in the transition zone and in cilia. A subset of sensory cilia in C. elegans contain a non-canonical transition zone with 7 and fewer doublet microtubules. We previously showed that this distinct transition zone is generated through microtubule loss in a canonical transition zone with 9 doublet microtubules, a process that occurs asynchronously during animal development. Here, we identify roles for the tubulin code and for an IFT cargo in generating a distinct transition zone. Sculpting of the distinct transition zone occurs in fully assembled cilia and transition zones and is independent of general ciliogenesis mechanisms. Our results demonstrate how specialized transition zones can be generated from canonical transition zones and provide insight into mechanisms of ciliary ultrastructural diversity and post-ciliogenesis restructuring. Such mechanisms hold the key to understanding ciliary function and to restoration of function in ciliopathies with ciliary ultrastructural defects.

cell biology↗

bioRxiv2021

Tracking extracellular vesicle (EV) cargo as a platform for studying EVomics, signaling, and targeting in vivo

Extracellular vesicle (EV)-based signaling is a challenge to study, due to EV small size, heterogeneity, and limited information on cargo content in vivo. We present Caenorhabditis elegans as a discovery platform that allows single EV tracking from source to target tissue in living animals. We enriched ciliary EVs using GFP-tagged PKD-2 cargo followed by mass spectrometry analysis to identify 2,888 cargo candidates. By integrating our dataset with single-cell transcriptomic data, we identified EV cargo produced by individual neurons and other cell and tissue types. A single cilium produces multiple EVs with distinct protein content. Ciliary EVs carry nucleic acid binding proteins. We observed transfer of EV cargo from the male reproductive tract to the hermaphrodite uterus during mating, a direct demonstration of animal-to-animal EV targeting. One-Sentence SummaryHere we present a discovery platform for studying animal extracellular vesicle composition and biogenesis.

cell biology↗

bioRxiv2020

Mutation of NEKL-4/NEK10 and TTLL genes opposes loss of the CCPP-1 deglutamylase and prevents neuronal ciliary degeneration

Ciliary microtubules are subject to post-translational modifications that act as a "Tubulin Code" to regulate motor traffic, binding proteins and stability. In humans, loss of CCP1, a cytosolic carboxypeptidase and tubulin deglutamylating enzyme, causes infantile-onset neurodegeneration. In C. elegans, mutations in ccpp-1, the homolog of CCP1, result in progressive degeneration of neuronal cilia and loss of neuronal function. To identify genes that regulate microtubule glutamylation and ciliary integrity, we performed a forward genetic screen for suppressors of ciliary degeneration in ccpp-1 mutants. We isolated the ttll-5(my38) suppressor, a mutation in the tubulin tyrosine ligase-like glutamylase gene. We show that mutation in ttll-4, ttll-5, or ttll-11 gene suppressed the hyperglutamylation-induced loss of microtubules and kinesin-2 mislocalization in ccpp-1 cilia. We also identified the nekl-4(my31) suppressor, an allele affecting the NIMA (Never in Mitosis A)-related kinase NEKL-4/NEK10. In humans, NEK10 mutation causes bronchiectasis, an airway and mucociliary transport disorder caused by defective motile cilia. C. elegans NEKL-4 does not localize to cilia yet plays a role in regulating axonemal microtubule stability. This work defines a pathway in which glutamylation, a component of the Tubulin Code, is written by TTLL-4, TTLL-5, and TTLL-11; is erased by CCPP-1; is read by ciliary kinesins; and its downstream effects are modulated by NEKL-4 activity. Identification of regulators of microtubule glutamylation in diverse cellular contexts is important to the development of effective therapies for disorders characterized by changes in microtubule glutamylation. By identifying C. elegans genes important for neuronal and ciliary stability, our work may inform research into human ciliopathies and neurodegenerative diseases.

genetics↗

bioRxiv2019

A ciliary BBSome-ARL-6-PDE6D pathway trafficks RAB-28, a negative regulator of extracellular vesicle biogenesis

Cilia both receive and send information, the latter in the form of extracellular vesicles (EVs). EVs are nano-communication devices that cells shed to influence cell, tissue, and organism behavior. Mechanisms driving ciliary EV biogenesis and environment release are almost entirely unknown. Here, we show that the ciliary G-protein RAB28, associated with human autosomal recessive cone-rod dystrophy, negatively regulates EV levels in the sensory organs of Caenorhabditis elegans. We also find that sequential targeting of lipidated RAB28 to periciliary and ciliary membranes is highly dependent on the BBSome and PDE6D, respectively, and that BBSome loss causes excessive and ectopic EV production. Our data indicate that RAB28 and the BBSome are key in vivo regulators of EV production at the periciliary membrane. Our findings also suggest that EVs control sensory organ homeostasis by mediating communication between ciliated neurons and glia, and that defects in ciliary EV biogenesis may contribute to human ciliopathies.

cell biology↗

bioRxiv2018

Cell type-specific structural plasticity of the ciliary transition zone in C. elegans

Background informationThe current consensus on cilia development posits that the ciliary transition zone (TZ) is formed via extension of nine centrosomal microtubules. In this model, TZ structure remains unchanged in microtubule number throughout the cilium life cycle. This model does not however explain structural variations of TZ structure seen in nature, and could also lend itself to the misinterpretation that deviations from nine-doublet microtubule ultrastructure represent an abnormal phenotype. Thus, a better understanding of events that occur at the TZ in vivo during metazoan development is required.\n\nResultsTo address this issue, we characterized ultrastructure of two types of sensory cilia in developing Caenorhabditis elegans. We discovered that, in cephalic male (CEM) and inner labial quadrant (IL2Q) sensory neurons, ciliary TZs are structurally plastic and remodel from one structure to another during animal larval development. The number of microtubules doublets forming the TZ can be increased or decreased over time, depending on cilia type. Both cases result in structural TZ intermediates different from TZ in adult cilia. In CEM cilia, axonemal extension and maturation occurs concurrently with TZ structural maturation.\n\nConclusions and SignificanceOur work extends the current model to include the structural plasticity of metazoan transition zone, which can be structurally delayed, maintained or remodeled in cell type-specific manner.

cell biology↗