Essential for the embryonic synthesis of chitin, a component of the eggshell. [(1->4)-N-acetyl-beta-D-glucosaminyl](n) + UDP-N-acetyl-alpha-D-glucosamine = [(1->4)-N-acetyl-beta-D-glucosaminyl](n+1) + H(+) + UDP egg-1, egg-2 and egg-3 maintain the homogenous distribution of chs-1 at the unfertilized oocyte cell membrane, thus ensuring the formation of a continuous and cohesive eggshell chitin layer (PubMed:20971008, PubMed:17869112). In the fertilized embryo, co-localizes with egg-3 to cytoplasmic foci in an egg-3-dependent manner (PubMed:17869112). Expressed at L3-L4 larval stages and in adults. RNAi-mediated knockdown causes the production of abnormal eggs characterized by a spherical morphology, the absence of the eggshell chitin layer, increased permeability to small molecules and a failure to divide (PubMed:16098962). Loss of polar body formation and loss of egg-3 and mbk-2 cortical localization in oocytes (PubMed:17869112). RNAi-mediated knockdown causes polyspermy in 40 percent of animals and a failure to internalize egg-1 after oocyte fertilization (PubMed:20971008). Simultaneous RNAi-mediated knockdown with mat-1 prevents the formation of the eggshell chitin layer (PubMed:20971008). Belongs to the chitin synthase family. Class IV subfamily.