(68) RNA Phase Transition Regulating Vertebrate Oocyte-to-Embryo Transition

Meng Ma¹; Sijie Chen¹ ; Hao-Chun Fan³ ; Jing Yang^1,2

1 Department of Comparative Biosciences, University of Illinois at Urbana-Champaign, Urbana, IL.
2 Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, IL.
3 Department of Animal Science, University of Illinois at Urbana-Champaign, Urbana, IL

Abstract Text:

During development, a fertilized egg develops into a multicellular organism that consists of a wide variety of types of cells. The organization and abundance of cellular machinery and organelles vary across different cell lineages, which enable cells to perform specialized functions. The dogma in the field is that the specific arrangement of the intracellular machinery is established gradually as the consequence of cellular differentiation. Currently, it is unclear if remodeling of the ER may facilitate cell fate determination and differentiation during development.

Our recent results reveal that remodeling of the ER during the oocyte-to-embryo transition is crucial for the asymmetric localization of RNAs in Xenopus oocytes. As asymmetric RNAs localization is essential for cell fate determination during early embryonic patterning, we hypothesized that remodeling of the ER may play an instructive role during cell fate determination and cellular differentiation. To test this hypothesis, we first analyzed the lineage specific-signature of the ER in early embryos. We found that the ER is uniquely associated with plasma membrane in the epidermis in early embryos. To determine if this ER-plasma membrane association is important for epidermal development, we asked if forced ER-plasma membrane association in non-epidermal tissue could promote epidermal development. To achieve this goal, we first screened for ER regulators using the Xenopus Tropicalis full-length clone set. Cracr2b was identified from this screen for its activity to induce ER-plasma membrane association. Overexpressing Cracr2b in meso-endodermal cells, where the ER is not associated with plasma membrane, caused abnormal gastrulation and patterning defects, including malformation of the head and shortened anterior-posterior axis. These findings suggest that ER remodeling might facilitate cell fate determination during early embryonic development.