Biology subjects

Finegan, T. M.

Publications and source records attributed to Finegan, T. M..

8 recordsLinked to original sources

bioRxiv2026

Fasciclin 2 Cooperates with Discs Large to Maintain Epithelial Architecture

Cell adhesion molecules of the immunoglobulin superfamily (IgCAMs) coordinate adhesive interactions with intracellular organization during tissue morphogenesis. In the Drosophila follicular epithelium, epithelial maintenance depends on reintegration, a process in which mitotically displaced cells reincorporate into the epithelial monolayer. Previous work identified the IgCAMs Fasciclin 2 (Fas2) and Neuroglian (Nrg) as parallel, partially redundant regulators of reintegration, but the intracellular mechanisms linking adhesion to reintegration remained unclear. Here, we show that Fas2 supports reintegration through two mechanistically distinct modes: a transmembrane mode and a GPI-linked mode. Although both contribute to reintegration, the transmembrane mechanism is more effective and depends on stabilization of a cortical Fas2 pool through intracellular coupling. Using yeast two-hybrid screening, genetics, and fluorescence recovery after photobleaching (FRAP), we identify the scaffold protein Discs large (Dlg1) as a functional intracellular partner of transmembrane Fas2. Partial disruption of Dlg1 preferentially sensitizes epithelia in which the parallel Nrg-dependent reintegration mechanism is compromised, consistent with Dlg1 functioning primarily within the Fas2-dependent reintegration arm. While Dlg1 is not required for Fas2 membrane localization, Dlg1 disruption increases the mobile fraction of transmembrane Fas2, indicating that Dlg1 promotes retention of a stabilized cortical Fas2 pool. Together, these findings support a model in which epithelial reintegration depends on coordinated adhesion-scaffold coupling and reveal mechanistic parallels between epithelial reintegration and IgCAM-dependent processes in the developing nervous system.

cell biology↗

bioRxiv2025

Beyond pulling: microtubule pushing forces contribute to robust spindle orientation in regular and irregular cell shapes

Oriented cell division is fundamental to development and tissue organization, requiring precise control of both spindle positioning and orientation. While cortical pulling forces mediated by dynein motor proteins are well-established drivers of spindle dynamics, the contribution of microtubule polymerization-based pushing forces remains unclear. We developed a generalizable computational biophysical model that integrates both pulling and pushing mechanisms to investigate spindle behavior across diverse cell types and geometries. This model successfully recapitulates experimental observations in three well-studied models: Drosophila follicular epithelial cells, Drosophila neuroblasts, and the early C. elegans embryo. Systematic analysis reveals that while pulling forces are the primary drivers of directed spindle orientation, pushing forces play crucial supporting roles by preventing spindle stalling and promoting alignment dynamics, particularly at high initial misalignment angles. We further applied our model to irregularly shaped zebrafish endothelial cells, which present unique challenges due to their non-spherical morphology and dynamic shape changes during mitosis. Our results demonstrate that asymmetric cortical force generator distributions, potentially localized at cell-cell junctions, can account for the observed off-center spindle positioning in these cells. This work provides a unified framework for understanding how the interplay between cell geometry, molecular polarity cues, and competing physical forces determines spindle dynamics, offering new insights into both canonical and non-canonical division orientations across cell types.

biophysics↗

bioRxiv2024

Fas2: A Tale of Two Chromosomes

The cell-cell adhesion molecule Fasciclin II (Fas2) has long been studied for its evolutionarily-conserved role in axon guidance. It is also expressed in the follicular epithelium, where together with a similar protein, Neuroglian (Nrg), it helps to drive the reintegration of cells born out of the tissue plane. Remarkably, one Fas2 protein null allele, Fas2G0336, demonstrates a mild reintegration phenotype, whereas work with the classic null allele Fas2EB112 showed more severe epithelial disorganization. These observations raise the question of which allele (if either) causes a bona fide loss of Fas2 protein function. The problem is not only relevant to reintegration but fundamentally important to understanding what this protein does and how it works: Fas2EB112 has been used in at least 37 research articles, and Fas2G0336 in at least three. An obvious solution is that one of the two chromosomes carries a modifier that either suppresses (Fas2G0336) or enhances (Fas2EB112) phenotypic severity. We find not only the latter to be the case, but identify the enhancing mutation as Nrg14, also a classic null allele.

genetics↗

bioRxiv2023

The Mechanical Influence of Densification on Initial Epithelial Architecture

Epithelial tissues are the most abundant tissue type in animals, lining body cavities and generating compartment barriers. The function of a monolayer epithelium - whether protective, secretory, absorptive, or filtrative -relies on regular tissue architecture with respect to the apical-basal axis. Using an unbiased 3D analysis pipeline developed in our lab, we previously showed that epithelial tissue architectures in culture can be divided into distinct developmental categories, and that these are intimately connected to cell density: at sparse densities, cultured epithelial cell layers have a squamous morphology (Immature); at intermediate densities, these layers develop lateral cell-cell borders and rounded cell apices (Intermediate); cells at the highest densities reach their full height and demonstrate flattened apices (Mature). These observations prompted us to ask whether epithelial architecture emerges from the mechanical constraints of densification, and to what extent a hallmark feature of epithelial cells, namely cell-cell adhesion, contributes. In other words, to what extent is the shape of cells in an epithelial layer a simple matter of sticky, deformable objects squeezing together? We addressed this problem using a combination of computational modeling and experimental manipulations. Our results show that the first morphological transition, from Immature to Intermediate, can be explained simply by cell crowding. Additionally, we identify a new division (and thus transition) within the Intermediate category, and find that this second morphology relies on cell-cell adhesion.

cell biology↗

bioRxiv2022

The spindle orienting machinery requires activation, not just localization

The orientation of the mitotic spindle at metaphase determines the placement of the daughter cells. Spindle orientation in animals typically relies on an evolutionarily conserved biological machine comprised of at least four proteins - called Partner of Inscuteable (Pins), Gi, Mushroom body defective (Mud), and Dynein in flies - that exert a pulling force on astral microtubules and reels the spindle into alignment. The canonical model for spindle orientation holds that the direction of pulling is determined by asymmetric placement of this machinery at the cell cortex. In most cell types, this placement is thought to be mediated by Pins, and a substantial body of literature is therefore devoted to identifying polarized cues that govern localized cortical enrichment of Pins. In Drosophila neuroblasts, for example, this cue is thought to be Inscuteable, which helps recruit Pins to the apical cell surface. In this study we revisit the canonical model. We find that spindle orientation in the follicular epithelium requires not only Pins localization but also activation, which relies on direct interaction between Pins and the multifunctional protein Discs large. This mechanism is distinct from the one mediated by Inscuteable, which we find also has an activating step. Together our results show that the canonical model is incomplete. Local enrichment of Pins is not sufficient to determine spindle orientation; an activation step is also necessary.

cell biology↗

bioRxiv2020

An Axon-Pathfinding Mechanism Preserves Epithelial Tissue Integrity

Dividing cells often move apically within epithelial tissue layers, likely to escape the spatial confinement of their neighbors. Because of this movement, daughter cells may be born displaced from the tissue layer. Reintegration of these displaced cells helps support tissue growth and maintain tissue architecture. In the Drosophila follicular epithelium, reintegration relies on the immunoglobulin-superfamily cell-adhesion molecules (IgCAMs) Neuroglian and Fasciclin 2, which line cell-cell borders1. These molecules have been described in epithelia, but are well-studied for their roles in neural development2-8. We show here that reintegration works in the same way as IgCAM-mediated axon growth and pathfinding; it relies not only on extracellular adhesion but also mechanical coupling between IgCAMs and the lateral Spectrin-Based Membrane Skeleton. Our work indicates that reintegration is mediated by a distinct epithelial cell-cell junction that is compositionally and functionally equivalent to junctions made between axons.

cell biology↗

bioRxiv2019

The tricellular vertex-specific adhesion molecule Sidekick facilitates polarised cell intercalation during Drosophila axis extension

In epithelia, tricellular vertices are emerging as important sites for the regulation of epithelial integrity and function. Compared to bicellular contacts, however, much less knowledge is available. In particular, resident proteins at tricellular vertices were identified only at occluding junctions, with none known at adherens junctions. In a previous study, we discovered that in Drosophila embryos, the adhesion molecule Sidekick (Sdk), well known in invertebrates and vertebrates for its role in the visual system, localises at tricellular vertices at the level of adherens junctions. Here, we survey a wide range of Drosophila epithelia and establish that Sdk is a resident protein at tricellular adherens junctions, the first of its kind. Clonal analysis suggests that pair-wise homophilic adhesion is necessary and sufficient for Sdk tricellular vertex localisation. Super-resolution imaging using structured illumination reveals that Sdk proteins form string-like structures at vertices. Postulating that Sdk may have a role in epithelia where adherens junctions are actively remodelled, we analysed the phenotype of sdk null mutant embryos during Drosophila axis extension, using quantitative methods. We find that apical cell shapes are strikingly abnormal in sdk mutants. Moreover, adhesion at apical vertices is compromised in rearranging cells, with holes forming and persisting throughout axis extension. Finally, we show that polarized cell intercalation is decreased and abnormal in sdk mutants. Mathematical modeling of the cell behaviours supports the conclusion that the T1 transitions of polarized cell intercalation are delayed in sdk mutants. We propose that this delay, in combination with a change in the mechanical properties of the converging and extending tissue, causes the striking cell shape phenotype of sdk mutant embryos.

developmental biology↗

bioRxiv2017

Bimodal Spindle Orientation Drives Tissue Regularity in a Proliferating Epithelium

We investigated the relationship between proliferation and tissue topology in an epithelial tissue undergoing elongation. We found that cell division is not required for elongation of the early Drosophila follicular epithelium, but does drive the tissue towards optimal geometric packing. To increase tissue regularity, cell divisions are oriented in the planar axis, along the direction of tissue expansion. Planar division orientation is governed by apico-cortical tension, which aligns with tissue expansion but not with interphase cell shape elongation. Hertwigs Rule, which holds that cell elongation determines division orientation, is therefore broken in this tissue. We tested whether this observation could be explained by anisotropic activity of the conserved Pins/Mud spindle-orienting machinery, which controls division orientation in the apical-basal axis. We found that Pins/Mud does not participate in planar division orientation. Rather, tension translates into planar division orientation in a manner dependent on Canoe/Afadin, which links actomyosin to adherens junctions. These findings demonstrate that division orientation in different axes - apical-basal and planar - is controlled by distinct, independent mechanisms in a proliferating epithelium.\n\nSummary StatementRegularity in a proliferating epithelium requires cells to divorce division orientation from interphase shape, which they accomplish by using distinct mechanisms to orient divisions in the apical-basal and planar axes.

developmental biology↗