Abstract
Microvilli are actin-filled membranous extensions common to epithelial cells. Several proteins have been identified that localize to microvilli. However, most of these proteins are dispensable for the normal morphogenesis of microvilli. Here, we show by immunoelectron microscopy that the non-classical cadherin Cad99C localizes to microvilli of Drosophila ovarian follicle cells. Loss of Cad99C function leads to disorganized and abnormal follicle cell microvilli. Conversely, overexpression of Cad99C in follicle cells results in large bundles of microvilli. Furthermore, altered microvilli morphology correlates with defects in the assembly of the vitelline membrane, an extracellular layer secreted by follicle cells that is part of the eggshell. Finally, we provide evidence that Cad99C is the homolog of vertebrate protocadherin 15. Mutations in the gene encoding protocadherin 15 lead to the disorganization of stereocilia, which are microvilli-derived extensions of cochlear hair cells, and deafness (Usher syndrome type 1F). Our data suggest an essential role for Cad99C in microvilli morphogenesis that is important for follicle cell function. Furthermore, these results indicate that insects and vertebrates use related cadherins to organize microvilli-like cellular extensions.
Highlights
Microvilli are extensions of the apical plasma membrane that are common to epithelial cells
We show by immunoelectron microscopy that the non-classical cadherin Cad99C localizes to microvilli of Drosophila ovarian follicle cells
Altered microvilli morphology correlates with defects in the assembly of the vitelline membrane, an extracellular layer secreted by follicle cells that is part of the eggshell
Summary
Microvilli are extensions of the apical plasma membrane that are common to epithelial cells. Microvilli contain a bundle of crosslinked actin filaments at their center that extend from the plasma membrane to the cell cortex Microvillar proteins, especially those of the intestinal brush border, have been identified. A normal-sized microvillar brush border can be assembled in the intestine of mice with defects in villin (Ferrary et al, 1999; Pinson et al, 1998). It seems that not all microvillar proteins are essential for microvilli morphogenesis. To understand the morphogenesis and function of microvilli better, it will be important to identify additional microvillar proteins and to test their requirement for the formation of microvilli
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