Abstract

Name: Margot Smit Affiliation: ZMBP , Tuebingen University, Germany

Title: Arrested Development: temporal regulation of cell identity during plant embryogenesis

Abstract:

Multicellularity allows organisms such as plants to form complex structures but these need to be carefully controlled in both space and time. What determines the relative timing of cell fate acquisition, progression, and differentiation along a cellular trajectory, and when/how is development slowed down or sped up? In our group, we investigate the mechanisms the plant uses to control the timing of two main cell fate transitions in the embryo: stomatal fate acquisition and differentiation.

Stomatal fate acquisition during embryogenesis is delayed: The stomatal initiator SPCH is present as soon as the embryonic cotyledon epidermis exists but does not induce stomatal fate acquisition for several days. This delay does not exist after germination: both in true leaves and in expanding cotyledons SPCH induces stomatal fate acquisition on the scale of hours rather than days. These findings indicate that currently unknown factors prevent initial stomatal lineage progression in the embryo. We are studying how stomatal regulation is differently wired during embryogenesis.

In addition to fate acquisition, stomatal differentiation is also delayed during embryogenesis. No cell types differentiate in the Arabidopsis embryo, but I found that factors that normally drive stomatal differentiation cannot do so during embryogenesis. We have now identified several mutants where stomatal cells undergo either full or partial differentiation and are trying to understand the underlying mechanisms responsible.

TALK 2 Name: Susan Wopat

Affiliation: UC Santa Barbara, CA, USA

Title: The zebrafish gastrula is shaped by stationary and germ layer–specific tissue flows

Abstract:

During gastrulation, cells collectively move to transform the blastula into a multilayered embryo. While genetic signaling pathways that establish body axes and cell fates are well characterized, how these programs coordinate the motion of tens of thousands of cells in vertebrate embryos remains unclear. To address this, we combine in toto live imaging, tissue-specific markers, and quantitative analyses to study germ layer dynamics in zebrafish embryos. By applying a user-friendly tissue cartography pipeline, we computationally separate the enveloping layer (EVL), epiblast, and mesoderm to analyze global shapes and cell flows in a tissue-specific manner. Examining tissues individually shows that each layer exhibits distinct, hours-long flow configurations that remain remarkably stable over time. This suggests that a sequence of stationary tissue flow modules transports cells to their destinations to build the unique tissue morphologies of the zebrafish gastrula. Mathematical decomposition further suggests that epiblast flow is strongly influenced by a superposition of convergent flow in the mesoderm and expansion flow in the EVL . Together, these results indicate that, despite the molecular complexity of development, vertebrate gastrulation is governed by emergent simplicity arising from robust physical principles, setting the stage for linking genetic signaling to tissue-scale dynamics.