Abstract
Gap junction (GJ) proteins, the primary constituents of GJ channels, are conserved determinants of patterning. Canonically, a GJ channel, made up of two hemi-channels contributed by the neighboring cells, facilitates transport of metabolites/ions. Here we demonstrate the involvement of GJ proteins during cuboidal to squamous epithelial transition displayed by the anterior follicle cells (AFCs) from Drosophila ovaries. Somatically derived AFCs stretch and flatten when the adjacent germline cells start increasing in size. GJ proteins, Innexin2 (Inx2) and Innexin4 (Inx4), functioning in the AFCs and germline respectively, promote the shape transformation by modulating calcium levels in the AFCs. Our observations suggest that alterations in calcium flux potentiate STAT activity to influence actomyosin-based cytoskeleton, possibly resulting in disassembly of adherens junctions. Our data have uncovered sequential molecular events underlying the cuboidal to squamous shape transition and offer unique insight into how GJ proteins expressed in the neighboring cells contribute to morphogenetic processes.
Highlights
In the metazoans, several temporally coordinated interconnected morphogenetic events are instrumental for the transformation of a young embryo into an adult
We demonstrate that heteromeric combination of gap junction proteins, Drosophila Innexin2 and Drosophila Innexin 4, expressed in the soma and germline of fly egg respectively, mediates the shape transition of cuboidal follicle cells to squamous fate
The two gap junction proteins likely participate as constituents of a calcium channel
Summary
Several temporally coordinated interconnected morphogenetic events are instrumental for the transformation of a young embryo into an adult. Depending on the individual cellular and/or developmental context, epithelial cells display distinct cell shape changes ranging from relatively simple ones like invagination, in-folding, and intercalation (convergent extension) to complex transformations including epiboly and branching morphogenesis [2]. One of the less explored aspects of epithelial morphogenesis is how the local intercellular interactions mediate these distinct shape changes during development. How these transitions are globally modulated, at a tissue level, to evolve a complex pattern is relatively unclear. Close physical interactions between the columnar cells of wing imaginal disc proper with the overlying squamous peripodial cells plays an integral role in mediating wing morphogenesis in flies [5]. All organ assemblies including skin, lung, trachea, cervix and cornea are critically dependent on proper interactions and inter-convertibility between the epithelial subtypes [6,7,8,9]
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