Septate junctions (SJs) perform an occluding function in invertebrate epithelia and consist of parallel septa extending across the intercellular space between neighbouring cells. In addition, they are required for several morphogenetic processes in arthropods. The biogenesis of SJs during development is inadequately studied and it was characterised in detail only for various epithelia of Drosophilamelanogaster. This paper provides a detailed analysis of the ultrastructural differentiation of SJs in the epidermis of the terrestrial isopod Porcellioscaber during embryonic and postembryonic development. In this study, mid-stage embryo S13 was the earliest stage in which single septa were observed basally to the adherens junction (AJ). Differentiation of SJs during further development includes gradual elongation of septa arrays and formation of continuous arrays of septa. The enlargement of SJs in the epidermis is most pronounced at the transition from embryonic to postembryonic development and after the release of mancae from the marsupium. SJs of postmarsupial mancae are similar to those of adults, but are not yet as extensive. Comparison of the differentiation of SJs in the epidermis and hindgut of P.scaber, reveals a similar sequence of events. In addition, remodelling of SJs was observed in the epidermis of late marsupial mancae, the stage of cuticle renewal. Common features of SJs' biogenesis in P.scaber and D.melanogaster ectodermal epithelia are indicated.
Keywords: Crustacea; embryo; epithelia; junctional complex; morphogenesis; ultrastructure.
Katja Kunčič, Polona Mrak, Nada Žnidaršič.