Required for normal developmental progression throughout all life stages (PubMed:18262516, PubMed:22466039). Specifically required for the molt stage during all larval transitions and morphogenesis (PubMed:18262516, PubMed:17267616, PubMed:22466039). Acts with heterochronic genes, including members of the let-7 family, to regulate larval stage to adult transition (PubMed:18262516, PubMed:28933985). Acts synergistically with acn-1 in let-7 regulated postembryonic cell division of hypodermal seam cells (PubMed:28933985). Acts in multiple pathways to influence daf-12 and daf-16 activity to in turn regulate physiological and reproductive processes such as body size and egg-laying (PubMed:22466039). May play a role in neurotransmission (PubMed:20862215). Interacts (via cytoplasmic domain) with feh-1 (via PID 2 domain). Expressed in the head, pharynx, spermatheca, uterus, vulva, tail and ventral neurons (PubMed:18262516). Specifically expressed in nerve ring interneurons, the ventral cord, socket and amphids in the head, with strong expression in junctional cells, including the pharyngeal intestinal valve and uterine seam junction, and the excretory cell and weak expression in epidermal epithelial cells, including hyp7 cells, vulval cells, rectal valve cells, pharyngeal arcade cells and the tail hypodermis (PubMed:20862215). Similar expression pattern in larval and adult cells with expression in neuronal, muscle, hypodermal and supporting cells (PubMed:17267616). Temporally expressed in seam cells from the middle of larval stage L4 and throughout adult stages (PubMed:18262516, PubMed:28933985). The NPXY motif mediates the interaction with clathrin. Extracellular region is proteolytically cleaved. Larval lethality during the L1 stage, with the formation of vacuoles in syncytial hypoderm, organ morphology defects, and molting defects (PubMed:17267616, PubMed:20862215). RNAi-mediated knockdown results in a reduced body size, transparent appearance, sluggish movement and insensitivity to touch (PubMed:18262516, PubMed:20862215). Delayed development and a molting defect that begins at the L3 to L4 larval stage transition and continues through to transition from the L4 larval stage to the young adult stage (PubMed:20862215). Increased sensitivity to acetylcholine inhibition (PubMed:20862215). Increased pharyngeal pumping (PubMed:11896189). In a let-7 mutant background, partial suppression of the let-7 bursting vulva phenotype (PubMed:28933985). Double RNAi-mediated knockdown with acn-1 in a let-7 mutant background leads to complete suppression of the heterochronic seam cell defects (PubMed:28933985). Lacks conserved metal-binding sites and has only weak affinity for copper in vitro. Belongs to the APP family.