Fig. 4. Embryonic phenotypes of cv-c mutants. Cuticle preparations of late embryos viewed under phase contrast showing the head skeleton (A,B), the posterior spiracles (C,D) and the dorsal cuticle (E,F). Wild-type (A,C,E), cv-c^M62 homozygote (B,D) and cv-c⁷ homozygote (F) embryos. (A) In wild-type embryos, the medial tooth occupies an internal position (arrowhead in A), whereas in 80% of cv-c^M62 embryos (B) the medial tooth is located on the exterior (arrowhead); the mouth hooks, which would normally be in this position, are displaced laterally (mouth hooks in A and B are indicated with asterisks). (C) A wild-type embryo with normal posterior spiracle morphology. The Filzkörper (black arrowhead), a filter formed in the internal tube connecting the spiracle to the tracheal system, is located inside the dome-like stigmatophore (white arrowhead). (D) In 28% of cv-c^M62 posterior spiracles analysed, the cells that form the Filzkörper do not invaginate and instead form a `lawn' on the exterior (black arrowhead). In 67% of posterior spiracles analysed, the Filzkörper cells invaginate but do so aberrantly such that the final Filzkörper is branched (white arrowhead). (E) A wild-type embryo with normal dorsal cuticle morphology. (F) A cv-c⁷ embryo showing puckering of the dorsal cuticle (arrowhead). (G,H) Stage 15 embryos stained with anti-SAS showing the latter stages of dorsal closure. (G) The leading edge cells of the lateral epidermis zip up along the dorsal midline (arrows) during stage 15 in wild-type embryos. (H) In cv-c mutant embryos, this process is delayed and less orderly. Arrows and arrowheads indicate the dorsal midline and regions of delayed closure. (I,J) Midgut morphology of stage 16 embryos visualised with the Fas3 antibody (which marks the visceral muscle overlying the midgut) in wild-type (I) or cv-c^M62 (J) embryos. The anterior-most constriction (1) does not occur in cv-c^M62 embryos, and the posterior-most constriction (3) is variably affected. (K-P) MpT morphology is disrupted in cv-c embryos. (K-N) MpT development visualised by staining with the Cut antibody, in wild-type (K,L) and cv-c^M62 embryos (M,N). Defects in cv-c^M62 embryos become obvious by stage 13 as the MpTs start their convergent extension movements (compare K with M). By stage 16, the wild-type MpTs have formed four long, thin tubules, positioned invariantly within the body cavity (L), whereas the cv-c^M62 MpTs have coalesced into a large cyst-like ball (N). Anterior (arrowhead) and posterior (asterisk) tubules are marked where they can be distinguished. (O,P) Nitrogenous waste products are excreted as urates that precipitate to form uric acid crystals in the acidic environment of the tubule lumen; these can be visualised in stage 17 embryos using polarised light. (O) A wild-type embryo, with normal posterior tubule morphology. (P) A cv-c^M62 homozygous embryo in which the MpTs have formed a cyst-like ball; urates are excreted into a large central lumen. (Q) A stage 16 cv-c mutant embryo in which wild-type cv-c has been expressed in the MpTs. The MpT phenotype is partially rescued. Embryos are shown from lateral (A-E,I,J,O,P) or dorsal (F-H,K-N,Q) perspectives.