Internal and external factors controlling cell shape

March 24, 2025 @ 12:15 pm to 01:15 pm

Magdalena Bezanilla, Dartmouth College

108 Wartik Laboratory
University Park

Abstract:
In multicellular organisms, often cell shape stems from restrictions imposed by the extracellular environment. Eukaryotes control this by building a wide variety of extracellular structures, ranging from bone and shell in animals to the silica-based cell walls in diatoms. These structures, which are often patterned over macroscopic scales, impose constraints on morphology. Yet, individual cells are responsible for depositing extracellular matrix. Thus, how organisms control large-scale patterning of their extracellular matrices is an open question. To tackle this question, my lab uses the highly polarized filamentous juvenile tissue of the model plant P. patens. This tissue is two dimensional and comprised of elongated cells. The apical cell in each filament actively divides giving rise to an apical and a differentiated subapical cell. Some subapical cells re-enter the cell cycle, generating a side-branch initial and forming a daughter filament. Growth and development of this tissue is easily continuously imaged over days and weeks in the microscope. Furthermore, genetic manipulation is routine allowing for the rapid generation of mutant plants as well as endogenous gene tagging resulting in lines that have fluorescently labeled proteins. We have found that disruption of the cytoskeleton, spatial cytosolic calcium gradients, master polarity regulators, and trafficking impact cell and tissue patterning. As an example, ROP, which is a small GTPase, is essential for polarized growth, branch formation, and development of adult tissues. ROP enrichment at the cell cortex predicts the site of cell expansion. Ongoing work aims to determine the molecular machinery that enables ROP to recruit the cytoskeleton and cell wall synthases to the active growth site, ultimately properly patterning the tissue and enabling development of adult tissues.

About the Speaker:
Magdalena Bezanilla is the E.E. Just Professor in the Biological Sciences Department at Dartmouth. She completed a BS degree in physics at UC Santa Barbara and a PhD at Johns Hopkins University where she worked with Tom Pollard to characterize the role of myosin II in cytokinesis in fission yeast. She transitioned to plant cell biology as a postdoctoral fellow working with Ralph Quatrano at Washington University. Dr. Bezanilla has pioneered the use of the moss Physcomitrium patens as a model system to interrogate how proteins within the cell direct and regulate extracellular matrix deposition ultimately impacting cell growth and morphogenesis. She has particularly focused on the regulation of the filamentous actin cytoskeletal network. The Bezanilla laboratory has developed such tools as RNA interference (RNAi), quantitative complementation analyses, rapid quantitative growth assays, CRISPR-Cas9 genome editing, and advanced imaging for use in P. patens to characterize cell growth and development. Using a multi-disciplinary approach, recent work has led to detailed models for polarized cell expansion, the influence of calcium, and the integration of cytoskeletal systems for directional persistence in growth. Current and future work aims to bring together multiple cell biological fields to determine how the extracellular matrix is patterned culminating in understanding how single cells shape organisms.

Contact

Alisa Chernikova
azc6415@psu.edu