Biology subjects

Pickett, M. A.

Publications and source records attributed to Pickett, M. A..

5 recordsLinked to original sources

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↗

bioRxiv2022

E-cadherin/HMR-1 and PAR-3 break symmetry at stable cell contacts in a developing epithelium

Tissue-wide patterning is essential to multicellular development, requiring cells to individually generate polarity axes and coordinate them in space and time with neighbors. Using the C. elegans intestinal epithelium, we identified a patterning mechanism informed by stabilized cell/cell contact and executed via the scaffolding protein PAR-3 and the transmembrane protein E-cadherin/HMR-1. Intestinal cells break symmetry as PAR-3 and HMR-1 recruit apical determinants into micron-scale local polarity complexes (LPCs) at homotypic contacts. LPCs undergo a HMR-1-based migration to a common tissue midline, thereby establishing tissue-wide polarity. Thus, symmetry breaking results from PAR-3-dependent intracellular polarization coupled to HMR-1-based tissue-level communication that occurs through a non-adhesive signaling role for HMR-1. Intestinal cells gain initial asymmetry from differential contact duration as homotypic contacts last longer than heterotypic contacts, thus providing stable platforms for LPC assembly and offering a logical and likely conserved framework for how internal epithelia with no obvious pre-existing asymmetries can polarize.

developmental biology↗

bioRxiv2021

Separable mechanisms drive local and global polarity establishment in the C. elegans intestinal epithelium

Apico-basolateral polarization is essential for epithelial cells to function as selective barriers and transporters, and to provide mechanical resiliency to organs. Epithelial polarity is established locally, within individual cells to establish distinct apical, junctional, and basolateral domains, and globally, within a tissue where cells coordinately orient their apico-basolateral axes. Using live imaging of endogenously tagged proteins and tissue specific protein depletion in the C. elegans embryonic intestine, we found that local and global polarity establishment are temporally and genetically separable. Local polarity is initiated prior to global polarity and is robust to perturbation. PAR-3 is required for global polarization across the intestine but is not required for local polarity establishment as small groups of cells are able to correctly establish polarized domains in PAR-3 depleted intestines in an HMR-1/E-cadherin dependent manner. Despite belonging to the same apical protein complex, we additionally find that PAR-3 and PKC-3/aPKC have distinct roles in the establishment and maintenance of local and global polarity. Together, our results indicate that different mechanisms are required for local and global polarity establishment in vivo. SUMMARY STATEMENTLive-imaging and intestine specific protein depletion reveal that apico-basolateral polarity establishment can be temporally and genetically separated at the local level of individual cells and globally, across a tissue.

cell biology↗

bioRxiv2020

Apical PAR complex proteins protect against epithelial assaults to create a continuous and functional intestinal lumen

Sustained polarity and adhesion of epithelial cells is essential for the protection of our organs and bodies, and this epithelial integrity emerges during organ development amidst numerous morphogenetic assaults. Using the developing C. elegans intestine as an in vivo model, we investigated how epithelial cells maintain integrity through cell division and elongation to build a functional tube. Live-imaging revealed that apical PAR complex proteins PAR-6/Par6 and PKC-3/aPkc remained apical during mitosis while apical microtubules and microtubule-organizing center (MTOC) proteins were transiently removed. Intestine-specific depletion of PAR-6, PKC-3, and the aPkc regulator CDC-42/Cdc42 caused persistent gaps in the apical MTOC as well as in other apical and junctional proteins after cell division and in non-dividing cells that elongated. Upon hatching, gaps coincided with luminal constrictions that blocked food, and larvae arrested and died. Thus, the apical PAR complex maintains apical and junctional continuity to construct a functional intestinal tube.

developmental biology↗

bioRxiv2019

Growth Cone-Localized Microtubule Organizing Center Establishes Microtubule Orientation in Dendrites

A polarized arrangement of neuronal microtubule arrays is the foundation of membrane trafficking and subcellular compartmentalization. Conserved among both invertebrates and vertebrates, axons contain exclusively "plus-end-out" microtubules while dendrites contain a high percentage of "minus-end-out" microtubules, the origins of which have been a mystery. Here we show that the dendritic growth cone contains a non-centrosomal microtubule organizing center (ncMTOC), which generates minus-end-out microtubules along outgrowing dendrites and plus-end-out microtubules in the growth cone. RAB-11-positive recycling endosomes accumulate in this region and are responsible for localizing the microtubule nucleation complex {gamma}-TuRC. The MTOC tracks the extending growth cone by kinesin-1/UNC-116-mediated endosome movements on distal plus-end-out microtubules and dynein-mediated endosome clustering near MTOC. Critically, perturbation of the function or localization of the MTOC causes reversed microtubule polarity in dendrites. These findings unveil the dendritic MTOC as a critical organelle for establishing axon-dendrite polarity.

cell biology↗