title: Innexin7a forms junctions that stabilize the basal membrane during cellularization of the blastoderm in Tribolium castaneum.
abstract: In insects, the fertilized egg undergoes a series of rapid nuclear divisions before the syncytial blastoderm starts to cellularize. Cellularization has been extensively studied in Drosophila melanogaster, but its thick columnar blastoderm is unusual among insects. We therefore set out to describe cellularization in the beetle Tribolium castaneum, the embryos of which exhibit a thin blastoderm of cuboidal cells, like most insects. Using immunohistochemistry, live imaging and transmission electron microscopy, we describe several striking differences to cellularization in Drosophila, including the formation of junctions between the forming basal membrane and the yolk plasmalemma. To identify the nature of this novel junction, we used the parental RNAi technique for a small-scale screen of junction proteins. We find that maternal knockdown of Tribolium innexin7a (Tc-inx7a), an ortholog of the Drosophila gap junction gene Innexin 7, leads to failure of cellularization. In Inx7a-depleted eggs, the invaginated plasma membrane retracts when basal cell closure normally begins. Furthermore, transiently expressed tagged Inx7a localizes to the nascent basal membrane of the forming cells in wild-type eggs. We propose that Inx7a forms the newly identified junctions that stabilize the forming basal membrane and enable basal cell closure. We put forward Tribolium as a model for studying a more ancestral mode of cellularization in insects.
authors.affiliation: Hubrecht Institute for Developmental Biology and Stem Cell Research, Uppsalalaan 8, Utrecht 3584 CT, The Netherlands Institute of Biology, Leiden University, Sylviusweg 72, Leiden 2333 BE, The Netherlands m.van.der.zee@biology.leidenuniv.nl.
authors.forename: Maurijn
authors.initials: M
authors.lastname: van der Zee
authors.affiliation: Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Benton
authors.affiliation: Institute of Biology, Leiden University, Sylviusweg 72, Leiden 2333 BE, The Netherlands.
authors.forename: Tania
authors.initials: T
authors.lastname: Vazquez-Faci
authors.affiliation: Institute of Biology, Leiden University, Sylviusweg 72, Leiden 2333 BE, The Netherlands.
authors.forename: Gerda E M
authors.initials: GE
authors.lastname: Lamers
authors.affiliation: Institute of Biology, Leiden University, Sylviusweg 72, Leiden 2333 BE, The Netherlands.
authors.forename: Chris G C
authors.initials: CG
authors.lastname: Jacobs
authors.affiliation: Hubrecht Institute for Developmental Biology and Stem Cell Research, Uppsalalaan 8, Utrecht 3584 CT, The Netherlands Department of Cell Biology, UMC Utrecht, 3584 CX Utrecht, The Netherlands.
authors.forename: Catherine
authors.initials: C
authors.lastname: Rabouille
mesh_terms: D000818:Animals; D001756:Blastoderm / Q000196:embryology*; D002462:Cell Membrane / Q000502:physiology; D017630:Connexins / Q000235:genetics / Q000378:metabolism*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000196:embryology; D018507:Gene Expression Regulation, Developmental; D007365:Intercellular Junctions / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism; D009024:Morphogenesis / Q000235:genetics; D034622:RNA Interference; D034741:RNA, Small Interfering; D014231:Tribolium / Q000196:embryology*
chemical_list: D017630:Connexins; D029721:Drosophila Proteins; D034741:RNA, Small Interfering; C120023:inx7 protein, Drosophila
keywords: Actin; Armadillo; Flour beetle; Parental RNAi; Time-lapse movie; Transient protein expression