title: A Pak-regulated cell intercalation event leading to a novel radial cell polarity is involved in positioning of the follicle stem cell niche in the Drosophila ovary.
abstract: In the germarium of the Drosophila ovary, germline cysts are encapsulated one at a time by a follicular epithelium derived from two follicle stem cells (FSCs). Ovaries in flies mutant for the serine/threonine kinase Pak exhibit a novel phenotype, in which two side-by-side cysts are encapsulated at a time, generating paired egg chambers. This striking phenotype originates in the pupal ovary, where the developing germarium is shaped by the basal stalk, a stack of cells formed by cell intercalation. The process of basal stalk formation is not well understood, and we provide evidence that the cell intercalation is driven by actomyosin contractility of DE-Cadherin-adhered cells, leading to a column of disk-shaped cells exhibiting a novel radial cell polarity. Cell intercalation fails in Pak mutant ovaries, leading to abnormally wide basal stalks and consequently wide germaria with side-by-side cysts. We present evidence that Pak mutant germaria have extra FSCs, and we propose that contact of a germline cyst with the basal stalk in the pupal ovary contributes to FSC niche formation. The wide basal stalk in Pak mutants enables the formation of extra FSC niches which are mispositioned and yet functional, indicating that the FSC niche can be established in diverse locations.
authors.affiliation: Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Vlachos
authors.affiliation: Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6.
authors.forename: Sharayu
authors.initials: S
authors.lastname: Jangam
authors.affiliation: Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6.
authors.forename: Ryan
authors.initials: R
authors.lastname: Conder
authors.affiliation: Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6.
authors.forename: Michael
authors.initials: M
authors.lastname: Chou
authors.affiliation: Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6 Departments of Anatomy and OB/GYN-RS, University of California, San Francisco, CA 94143, USA.
authors.forename: Todd
authors.initials: T
authors.lastname: Nystul
authors.affiliation: Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6 nharden@sfu.ca.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Harden
mesh_terms: D000818:Animals; D016764:Cell Polarity; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000033:anatomy & histology / Q000166:cytology* / Q000201:enzymology*; D005260:Female; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D006080:Ovarian Follicle / Q000166:cytology* / Q000201:enzymology*; D010063:Ovum / Q000166:cytology / Q000378:metabolism; D010641:Phenotype; D055153:Stem Cell Niche; D054462:p21-Activated Kinases
chemical_list: D029721:Drosophila Proteins; C099277:Pak protein, Drosophila; D054462:p21-Activated Kinases
keywords: Basal stalk; Cell intercalation; Drosophila; Follicle stem cell; Ovary; Pak