Biology

Dr. Muriel Grammont
Ecole Normale Supérieure de Lyon, France

Epithelial cell morphogenesis is an essential process for animal development. Epithelia are composed of polarized cells with a basal side interacting through Integrins with a basement membrane (BM) and a lateral side containing cadherin-based junctional complexes. Integrins and Cadherins are both linked to actin filaments and are thus involved in cell shape regulation. The model we are using to study epithelial morphogenesis is the follicular epithelium in Drosophila melanogaster. It consists of a monolayer of 800 epithelial cells that surround an internal cluster of 16 germline cells (15 nurse cells and one posteriorly-localized oocyte), and that are covered by an external BM. During follicle development, the epithelial cells undergo a cuboidal-to-squamous transition around the nurse cells. Others and we have previously shown that cell flattening depends on Cadherin-based adherens junction remodelling and depends on the growth of the germline. Our aim is to define the genetic and mechanical processes driving cell flattening by looking at the contribution of the germline, of the BM and of the epithelial cells. To analyse the role of the germline growth, we are measuring the osmotic pressure within the germline in WT and in mutants with altered growth by using an atomic force microscope (AFM), and analyse the impacts of these mutants on the flattening of the squamous cells. To analyse the role of the BM, we also use an AFM to determine its mechanical properties, and analyse the consequence of lack of Collagen and/or Integrins signalling on cell flattening. Altogether, our results demonstrate the importance of mechanical properties of tissues interacting with epithelial cells for their morphogenesis.