Fig. 4. Depiction of vulval induction in the context of the whole animal. (A) A schematic transverse section through a developing hermaphrodite. The dorsal side of the worm is up. Dorsal and ventral nerve cord, blue circles labeled N; body-wall muscles in the four lateral quadrants, red cells labeled Mu; gonadal tissue, inverted U-shaped tissue; anchor cell, green circle labeled AC. Representative vulval precursor cell (grey cell labeled VPC). (B) One model for EGL-30 modulation of LET-23-mediated vulva development. Neurons (blue, N) are directly stimulated by environmental conditions and transduce a signal to muscle (red, Mu) via EGL-30, and possibly the UNC-13 and UNC-64 synaptic transmission proteins. Excitation of muscle by neuronally expressed (and possibly also by muscle-expressed) EGL-30 leads to activation of downstream components that include EGL-19 voltage-gated calcium channels. The muscle cells provide a modulatory signal that may upregulate BAR-1 activity in P6.p (grey cell, VPC) to cooperate with LIN-3 from the anchor cell (green, AC) to facilitate vulval induction. Hyp, hypodermis; Int, intestine.