Developmental genetics of the Caenorhabditis elegans pharynx

Advanced Review

Marc Pilon

Published Online: May 23 2014

DOI: 10.1002/wdev.139

Full article on Wiley Online Library: HTML PDF

Can't access this content? Tell your librarian.

The Caenorhabditis elegans pharynx is a rhythmically pumping organ composed initially of 80 cells that, through fusions, amount to 62 cells in the adult worm. During the first 100 min of development, most future pharyngeal cells are born and gather into a double‐plate primordium surrounded by a basal lamina. All pharyngeal cells express the transcription factor PHA‐4, of which the concentration increases throughout development, triggering a sequential activation of genes with promoters responding differentially to PHA‐4 protein levels. The oblong‐shaped pharyngeal primordium becomes polarized, many cells taking on wedge shapes with their narrow ends toward the center, hence forming an epithelial cyst. The primordium then elongates, and reorientations of the cells at the anterior and posterior ends form the mouth and pharyngeal‐intestinal openings, respectively. The 20 pharyngeal neurons establish complex but reproducible trajectories using ‘fishing line’ and growth cone‐driven mechanisms, and the gland cells also similarly develop their processes. The genetics behind many fate decisions and morphogenetic processes are being elucidated, and reveal the pharynx to be a fruitful model for developmental biologists. WIREs Dev Biol 2014, 3:263–280. doi: 10.1002/wdev.139 This article is categorized under: Gene Expression and Transcriptional Hierarchies > Cellular Differentiation Invertebrate Organogenesis > Worms Nervous System Development > Worms

Overview of pharyngeal development. All pharyngeal cells are descendants of the ABa and MS cells which are born after 2 and 3 cell divisions of the zygote, respectively (a). ABa will produce 49 pharyngeal cells while MS will produce 39. These cells are born and migrate during gastrulation (b) to form two plates of cells 6–8 cells deep along the dorsal–ventral axis (c). Many cells then constrict along the midline facing apical surfaces to create an elongated epithelial cyst depicted as a cross section in (d). Reorientation of the cells at the anterior and posterior ends of the primordium create openings toward the mouth and intestine, and retraction of the apical tips of marginal cells create a lumen that runs through the entire pharynx as it elongates; thin cellular processes, such as the axons of the M2 and other neurons, are drawn by cellular elongations such as that of the pm5 muscle cells in the isthmus (e). Pharyngeal cells then complete their differentiation and morphogenesis, including completing growth cone‐driven axon trajectories, to produce a mature pharynx that will grow in size during larval development and of which the muscle cells will gradually become disorganized during aging (f). See text for details. The lineage is from Sulston et al., and the developmental processes shown are mostly from Portereiko and Mango, Rasmussen et al. and Rauthan et al.