Figure 1. Pharynx/valve morphogenesis.

Top, differential interference contrast micrograph of a C. elegans larva, false colored to highlight the pharynx, valve and intestine. Bottom, diagram illustrating major stages in the formation of the cyst, and subsequent events as described in this report on the morphogenesis of the valve tube from the cyst; the diagram shows transverse views of all stages. Future pharyngeal and valve cells aggregate into an intermediate structure called the double plate. Laminin (bold black) at the periphery, or basal surface, of the double plate cues the opposite localization of apical proteins (blue), and apical constriction transforms the double plate into a cyst. Two future valve cells (red, called v3D and v3V) dock at the left-right boundary of the intestinal primordium (yellow). Docking begins slightly before, and continues during, apical constriction. The v3 valve cells remain at the left-right boundary until the two intestinal cells divide and form the final, four-cell terminus of the intestine. Valve cells and other cells in the cyst appear to explore their neighbors through actin-rich lamellipodia, and in many cases reposition their cell bodies. pm8 (green) and valve cells wrap partially or completely around the midline, thereby extruding the valve tube from the cyst.