Biology subjects

Holcomb, M. C.

Publications and source records attributed to Holcomb, M. C..

3 recordsLinked to original sources

bioRxiv2024

The role of local and long-range stresses in cephalic furrow formation in the Drosophila melanogaster embryo

Cephalic furrow (CF) is a transient epithelial invagination that forms during early gastrulation in the Drosophila melanogaster embryo. The initial stage of cephalic furrow formation (CFF) involves a shortening of initiator cells, generation of a localized asymmetric protrusion inwards, and then subsequent descent of cells into the yolk sac area. We present an analysis of how local forces associated with cell-membrane tensions and cell pressures interact with the long-range tensile stress developing along the furrow to generate the invagination. We propose two numerical models which capture different aspects of CFF. First, we formulate a force-center model of CF to show how the spatiotemporal heterogeneity of initiator-cell activation observed in vivo is a result of tensile-stress-feedback-based intercellular coordination. We also argue that this kind of mechanical stress-based activation mechanism likely contributes to robustness of the overall process. Second, we use our multi-node lateral vertex model to analyze the mechanical dynamics of the anterior-posterior cross-section of CF. This approach allows us to quantify the balance between cortical membrane tension forces, cellular pressures, and the inward force produced by the tension along the curved apical surface of the embryo. Comparing our simulations to experimental images, we discuss the crucial and indispensable role of the tension-induced inward force, especially during the initial stages of CFF where the localized asymmetric protrusion is formed. We argue that without this inward force the initial descent of the initiator cells into the furrow would not be possible, and that at later stages the inward force provides redundancy to this process and thus aids CFF robustness.

biophysics↗

bioRxiv2023

The mechanics of cephalic furrow formation in the Drosophila embryo

Cephalic furrow formation (CFF) is a major morphogenetic movement during gastrulation in Drosophila melanogaster embryos that gives rise to a deep, transitory epithelial invagination. Recent studies have identified the individual cell shape changes that drive the initiation and progression phases of CFF; however, the underlying mechanics of these changes are not yet well understood. During the progression phase, the furrow deepens as columnar cells from both the anterior and posterior directions fold inwards rotating by 90{degrees}. To analyze the mechanics of this process, we have developed an advanced 2D vertex model, which introduces multi-node representation of cellular membranes and allows us to capture the membrane curvature associated with pressure variation. Our investigations reveal some key mechanical features of CFF. As cells begin to roll over the cephalic furrow cleft, they become wedge-shaped as their apical cortices and overlying membranes expand, lateral cortices and overlying membranes release tension, internal pressures drop, and basal cortices and membranes contract. Cells then reverse the process by shortening apical cortices and membranes, increasing lateral tension, and causing internal pressures to rise. Since the basal membranes expand, the cells recover a rotated columnar shape at the end of this process. Interestingly, our findings indicate that the basal membranes may be passively reactive throughout the progression phase. We also find that the smooth rolling of cells over the cephalic furrow cleft necessitates that internalized cells provide a solid base through high membrane tensions and internal pressure levels, which allows transmission of tensile force that pulls new cells into the furrow. These results lead us to suggest that CFF may help establish a baseline tension across the apical surface of the embryo that would facilitate cellular coordination of other morphogenetic movements via mechanical stress feedback mechanisms. SIGNIFICANCEMechanical forces and stress feedback are essential for the development of morphology and structure in the embryo. Although great progress has been made in understanding the genetic control of patterning and cell fate, mechanical stress contributions are not as well understood. Mechanical analyses of the apical constrictions initiating ventral furrow formation and subsequent invagination dynamics in Drosophila have shed considerable light on these processes; however, ventral furrow formation is only one of many morphogenetic movements. Cephalic furrow formation occurs simultaneously with ventral furrow formation, but its cell shape changes and invagination dynamics are radically different. This study shows that mechanical forces and feedback operating in cephalic furrow formation also differ considerably from those in ventral furrow, demonstrating a potentially wide array of mechanical processes in morphogenesis.

biophysics↗

bioRxiv2019

Mechanical Feedback and Robustness of Apical Constrictions in Drosophila Embryo Ventral Furrow Formation

Formation of the ventral furrow in the Drosophila embryo relies on the apical constriction of cells in the ventral region to produce bending forces that drive tissue invagination. Recently [J Phys Condens Matter. 2016;28(41):414021], we observed that apical constrictions during the initial phase of ventral furrow formation produce elongated patterns of cellular constriction chains prior to invagination, and argued that these are indicative of tensile stress feedback. Here, we quantitatively analyze the constriction patterns preceding ventral furrow formation and find that they are consistent with the predictions of our active-granular-fluid model of a monolayer of mechanically coupled stress-sensitive constricting particles. Our model shows that tensile feedback causes constriction chains to develop along underlying precursor tensile stress chains that gradually strengthen with subsequent cellular constrictions. As seen in both our model and available optogenetic experiments, this mechanism allows constriction chains to penetrate or circumvent zones of reduced cell contractility, thus increasing the robustness of ventral furrow formation to spatial variation of cell contractility by rescuing cellular constrictions in the disrupted regions.

biophysics↗