Fig. 4. Apical localisation of innexin 2 mRNA. In situ hybridisation using digoxigenin (A-D) or fluorescein-labelled RNA innexin 2 antisense riboprobes (E-G). (A) innexin 2 transcripts are detected in the cytoplasm of the nurse cells (nc) and the oocyte (oc) during oogenesis. Note the localisation of the mRNA in the cortical region of the oocyte and the border cells (arrows). (B) Blastoderm embryo. Transcripts are ubiquitously distributed. (C) Germ band extension stage. mRNA expression occurs in the invaginating stomodeum (st), the anterior midgut primordium (amg) that abuts the involuted foregut tube, in the proctodeum (p) and in segment precursors (Stebbings et al., 2000). (D) During keyhole formation, innexin 2 expression is found in the ectodermal (ec) and endodermal (en) tissue regions of the proventriculus primordium (arrow marks the boundary). Note that the innexin 2 mRNA expression pattern corresponds to the reporter gene expression pattern of the P lines (compare with Fig. 1). (E-G) Double immunostaining of a proventriculus of a stage 16 embryo (marked by the stippled line) using a fluorescein-labelled RNA innexin 2 antisense riboprobe (E; red) and anti-Discs lost antibody (F; green), which marks the apical (ap, shown by arrows) sides of epithelial cells (Bhat et al., 1999). innexin 2 mRNA is localised to the apical sides of the proventricular cells (merge in G).

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