Biology subjects

Magescas, J.

Publications and source records attributed to Magescas, J..

5 recordsLinked to original sources

bioRxiv2025

Inactivation of microtubule organizing center function of the centrosome is required for neuronal development and centriole elimination

Cell differentiation is marked by a dramatic reorganization of the microtubule cytoskeleton that enables diverse cell functions. Mitotic precursor cells arrange microtubules around centrosomes, which become activated as microtubule-organizing centers (MTOCs) through the recruitment of pericentriolar material (PCM) and microtubules to build the mitotic spindle. A hallmark of differentiation is the "inactivation" of centrosomal MTOC function through the loss of PCM and microtubules, yet the function of this inactivation is unknown. We developed a GFP-nanobody-based targeting tool to activate centrosomes in C. elegans differentiated cells. Ectopically activating centrosomes in sensory neurons perturbed microtubule polarity, dynein-mediated trafficking, and caused defects in cell morphology and dendrite pathfinding. Ectopic PCM perturbed ciliogenesis and also protected centrioles from elimination, another common feature of differentiation. By forcing centrosome activation in a fully differentiated cell in a developing organism, we show that centrosome inactivation is required for differentiation by directly contributing to cell form and function.

cell biology↗

bioRxiv2025

Reciprocal E-cadherin signaling aligns apical surfaces between neighboring epithelial tissues to complete the C. elegans digestive tract

Epithelial cells form barriers with specialized apical membranes facing the external environment or internal lumens, yet how interconnected epithelial tubular systems form from cystic epithelial primordia is poorly studied. At the boundaries of cystic epithelial primordia, apical surfaces must correctly align to yield functional connections within and between organs. Here, we use the digestive tract of the developing C. elegans embryo to define a crucial two-cell tissue, the rectal valve (vir) cells, that mediate the connection and apical alignment between the posterior intestine and the rectum. Vir cells migrate while attached to the rectal primordium to create an essential connection with the intestinal primordium and complete the digestive tract. Vir contact with the intestine, through E-cadherin signaling, is required for the intestinal apical surface to undergo a transition from a cyst with an inaccessible apical surface to an open tube competent to connect with neighboring tissues. Ablation of vir cell progenitors results in a lethal disconnection between the intestinal and rectal apical surfaces due to failure of this first step in apical accessibility. To resolve the final gap in apical continuity between the intestine and rectum, vir cells develop bipolar apical surfaces, each facing the neighboring tissue. The intestine-facing apical puncta in vir require intestinal E-cadherin signaling to form and accumulate as well as to correctly partition apical proteins within vir cells. Together these results establish E-cadherin-based signaling as the crucial factor aligning apical surfaces across primordia as epithelial cells from different germ layers form a vital connection.

developmental biology↗

bioRxiv2023

MAP9/MAPH-9 supports axonemal microtubule doublets and modulates motor movement

Microtubule doublets (MTDs) are a well conserved compound microtubule structure found primarily in cilia. However, the mechanisms by which MTDs form and are maintained in vivo remain poorly understood. Here, we characterize microtubule-associated protein 9 (MAP9) as a novel MTD-associated protein. We demonstrate that C. elegans MAPH-9, a MAP9 homolog, is present during MTD assembly and localizes exclusively to MTDs, a preference that is in part mediated by tubulin polyglutamylation. Loss of MAPH-9 caused ultrastructural MTD defects, dysregulated axonemal motor velocity, and perturbed cilia function. As we found that the mammalian ortholog MAP9 localized to axonemes in cultured mammalian cells and mouse tissues, we propose that MAP9/MAPH-9 plays a conserved role in supporting the structure of axonemal MTDs and regulating ciliary motors.

cell biology↗

bioRxiv2020

Centriole-less pericentriolar material serves as a microtubule organizing center at the base of C. elegans sensory cilia

During mitosis in animal cells, the centrosome acts as a microtubule organizing center (MTOC) to assemble the mitotic spindle. MTOC function at the centrosome is driven by proteins within the pericentriolar material (PCM), however the molecular complexity of the PCM makes it difficult to differentiate the proteins required for MTOC activity from other centrosomal functions. We used the natural spatial separation of PCM proteins during mitotic exit to identify a minimal module of proteins required for centrosomal MTOC function in C. elegans. Using tissue specific degradation, we show that SPD-5, the functional homolog of CDK5RAP2, is essential for embryonic mitosis while SPD-2/CEP192 and PCMD-1, which are essential in the zygote, are dispensable. Surprisingly, although the centriole is known to be degraded in the ciliated sensory neurons in C. elegans [1-3], we find evidence for "centriole-less PCM" at the base of cilia and use this structure as a minimal testbed to dissect centrosomal MTOC function. Super-resolution imaging revealed that this PCM inserts inside the lumen of the ciliary axoneme and directly nucleates the assembly of dendritic microtubules towards the cell body. Tissue-specific degradation in ciliated sensory neurons revealed a role for SPD-5 and the conserved microtubule nucleator {gamma}-TuRC, but not SPD-2 or PCMD-1, in MTOC function at centriole-less PCM. This MTOC function was in the absence of regulation by mitotic kinases, highlighting the intrinsic ability of these proteins to drive microtubule growth and organization and further supporting a model that SPD-5 is the primary driver of MTOC function at the PCM.

cell biology↗

bioRxiv2018

A two-step mechanism for the inactivation of microtubule organizing center function at the centrosome

SummaryDuring mitosis, the centrosome acts as a microtubule organizing center (MTOC), orchestrating microtubules into the mitotic spindle through its pericentriolar material (PCM). This activity is biphasic, cycling through assembly and disassembly during the cell cycle. Although hyperactive centrosomal MTOC activity is a hallmark of some cancers, little is known about how the centrosome is inactivated as an MTOC. Analysis of endogenous PCM proteins in C. elegans revealed that the PCM is composed of distinct protein territories that are removed from the centrosome at different rates and using different behaviors. Inhibition of PP2A phosphatases stabilized the PCM and perturbation of cortical pulling forces altered the timing and behavior by which proteins were removed from the centrosome. These data indicate that PCM disassembly is a two-step process, beginning with a phosphatase-dependent dissolution of PCM proteins followed by the ejection of ruptured PCM by cortical forces, ultimately inactivating MTOC function at the centrosome.

cell biology↗