Fig. 4. Localization of spn-4 mRNA. Wild-type embryos were analyzed by in situ hybridization with a spn-4 cDNA probe. Anterior is leftwards, posterior is rightwards, dorsal is upwards and ventral is downwards. Scale bar: 10 µm. (A) One-cell embryo. (B) Two-cell embryo. (C) Four-cell embryo. (D) Eight-cell embryo. P3 and C are stained. (E) An embryo just before gastrulation. P4 and D are stained. (F) An embryo beginning gastrulation. Only P4 is stained. (G) An embryo during gastrulation. P4 has divided to produce Z2 and Z3, which are stained. (H) A mid-stage embryo. No staining is observed. The spn-4 mRNA was also detected in adult gonads and in oocytes (data not shown).