Comparison of the classical model of myeloid cell homeostasis and LC homeostasis. (A) Classical model for cell proliferation and differentiation. Precursors are located in a niche (e.g., the bone marrow), self-renew, and give rise to proliferating committed progenitors and precursors. Precursors with a limited differentiation potential migrate to the peripheral tissue and complete their differentiation. During the life of the animal, when differentiated cells die, new precursors will migrate from the bone marrow to replace them. (B) LC precursors are recruited into the epidermis as a single wave before birth and differentiate in situ, and then proliferate to form a network. No further input from the progenitors is needed. During life, differentiated cells can enter the cell cycle when required.