1 CHAPTER 9 LATROPHILIN SIGNALLING IN TISSUE POLARITY AND MORPHOGENESIS Tobias Langenhan* and Andreas P. Russ* Abstract: Understanding the mechanisms that coordinate the polarity of cells and tissues during embryogenesis and morphogenesis is a fundamental problem in developmental biology. We have recently demonstrated that the putative neurotoxin receptor lat-1 defines a mechanism required for the alignment of cell division planes in the early embryo of the nematode C. elegans. Our analysis suggests that lat-1 is required for the propagation rather than the initial establishment of polarity signals. Similar to the role of the flamingo/CELSR protein family in the control of planar cell polarity, these results implicate an evolutionary conserved subfamily of adhesion-GPCRs in the control of tissue polarity and morphogenesis. INTRODUCTION A fundamental requirement in all multicellular organisms is a robust program to achieve the correct spatial arrangement of cells. Cell fate decisions, the orientation of mitotic divisions, the migration of individual cells and morphogenetic movements of cell groups have to be tightly coordinated. While our understanding of the molecular mechanisms controlling asymmetric cell fate decisions and mitotic spindle orientation in certain types of cell-cell interaction is advanced (reviewed in refs. 1,2), it is less well understood how signals are propagated in larger groups of cells to align cell polarity and division plane orientation and how tissue polarity is coordinated with morphogenetic movements. The analysis of planar cell polarity (PCP) in epithelial sheets and the study of convergence and extension (C and E) movements during gastrulation in vertebrates have implicated signalling by the Wnt/PCP, Fat/Dachsous/Four-jointed (Fat/Ds/Fj) and *Corresponding Author: Tobias Langenhan—Institute of Physiology, University of Würzburg, 97070 Würzburg, Germany. Email: tobias.langenhan@uni-wuerzburg.de *Corresponding Author: Andreas Russ—Department of Biochemistry, University of Oxford, OX1 3QU, Oxford, UK. Email: andreas.russ@bioch.ox.ac.uk Adhesion-GPCRs: Structure to Function, edited by Simon Yona and Martin Stacey. ©2010 Landes Bioscience and Springer Science+Business Media.