Filamin is a large, highly versatile structural and signaling scaffold of the cytoskeleton, interacting primarily with filamentous actin and integrins. Filamin is composed of an N-terminal actin-binding domain, and many immunoglobulin (Ig)-like repeats. The C-terminal Ig-like repeats of filamin act as a mechanical sensor by changing conformation under stress, and hence differentially interacting with downstream effectors. The C. elegans genome contains five predicted filamin-like genes (WormBase WS199); however, the predicted filamin-like open reading frames (ORFs) lack one or more features characteristic of filamin. Interestingly, the filamin genes are found in two clusters on chromosome IV (ORFs Y66H1B.2, Y66H1B.5, Y66H1B.3) and chromosome X (ORFs C23F12.2, C23F12.1). Our cDNA sequencing suggests that each cluster encodes a full-length, well-conserved filamin gene, as well as additional splice variants including N- and C-terminal truncations. Our analysis of the filamin mutant Y66H1B.3 (
tm545) and RNAi treated animals suggest Y66H1B filamin is essential for ovulation in C. elegans, and likely acts as a stretch sensor to potentiate dilation of the spermatheca-uterine (sp-ut) valve. Analysis of animals expressing Y66H1B.3p::GFP fusion constructs suggests filamin is expressed in the gonadal sheath cells, spermatheca, and uterus. Y66H1B.3 (
tm545) and Y66H1B RNAi, display a dramatic ovulation defect: oocytes are entrapped in the spermatheca following fertilization due to failure of the sp-ut valve to dilate. The actin cytoskeleton of the spermathecal and uterine cells is disorganized, with predominantly thick, cortical actin filaments. Mosaic analysis of rescued
tm545 animals suggests Y66H1B filamin function is cell-autonomous in the spermatheca. We propose the C. elegans reproductive system as a novel, multicellular, myoepithelial model for study of filamin and mechanosensation that will allow genetic and molecular dissection of the mechanism by which cells respond to physical forces. .