Konkol, A. | bioRxiv Science

bioRxiv2023

Swimming, Feeding and Inversion of Multicellular Choanoflagellate Sheets

The recent discovery of the striking sheet-like multicellular choanoflagellate species Choanoeca flexa that dynamically interconverts between two hemispherical forms of opposite orientation raises fundamental questions in cell and evolutionary biology, as choanoflagellates are the closest living relatives of animals. It similarly motivates questions in fluid and solid mechanics concerning the differential swimming speeds in the two states and the mechanism of curvature inversion triggered by changes in the geometry of microvilli emanating from each cell. Here we develop fluid dynamical and mechanical models to address these observations and show that they capture the main features of the swimming, feeding, and inversion of C. flexa colonies.

biophysics↗

bioRxiv2020

LEAFY is a pioneer transcription factor and licenses cell reprogramming to floral fate

Master transcription factors reprogram cell fate in multicellular eukaryotes. Pioneer transcription factors have prominent roles in this process because of their ability to contact their cognate binding motifs in closed chromatin. Reprogramming is pervasive in plants, whose development is plastic and tuned by the environment, yet no bonafide pioneer transcription factor has - been identified in this kingdom. Here we show that the master transcription factor LEAFY (LFY), which promotes floral fate through upregulation of the floral commitment factor APETALA1 (AP1), is a pioneer transcription factor. In vitro, LFY binds in a sequence-specific manner and with high affinity to the endogenous AP1 target locus DNA assembled into a nucleosome. In vivo, LFY associates with nucleosome occupied binding sites at the majority of its target loci, including AP1, where it co-occupies DNA with histones. Moreover, the LFY DNA contact helix shares defining properties with those of strong nucleosome binding pioneer factors. At the AP1 locus, LFY unlocks chromatin locally by displacing the H1 linker histone and by recruiting SWI/SNF chromatin remodelers, but broad changes in chromatin accessibility occur later and require activity of additional, non-pioneer transcription, factors. Our study provides a mechanistic framework for patterning of inflorescence architecture and uncovers striking similarities between plant and animal pioneer transcription factors. Further analyses aimed at elucidating the defining characteristics of pioneer transcription factors will allow harnessing these for enhanced cell fate reprogramming.

plant biology↗