Adult neurogenesis in crayfish: Identity and regulation of neural progenitors produced by the immune system

Adult-born neurons are incorporated into brain circuits in the crayfish Procambarus clarkii, as in many vertebrate and invertebrate species. Adult neurogenesis depends on several conserved features, including the presence of neurogenic niches housing progenitor cells and the expansion, migration, and differentiation of their daughters, the neural precursor cells. However, in contrast to mammalian species, the progenitors initiating the neurogenic lineage in P. clarkii do not undergo long-term self-renewal. A central question is the mode of replenishment of these cells. Experiments have shown that hemocytes generated by the immune system, and not other cell types, are attracted to and incorporated into the niche. The present studies highlight the interdependency of the immune and nervous systems in the generation of adult-born neurons, by demonstrating that hyaline hemocytes are the probable neural progenitor cells, and that serotonin and the cytokine astakine 1 regulate both immune function and adult neurogenesis.