d -Serine controls epidermal vesicle release via NMDA receptor, allowing tissue migration during the metamorphosis of the chordate Ciona

Abstract

d -Serine, a free amino acid synthesized by serine racemase, is a coagonist of N -methyl- d -aspartate–type glutamate receptor (NMDAR). d -Serine in the mammalian central nervous system modulates glutamatergic transmission. Functions of d -serine in mammalian peripheral tissues such as skin have also been described. However, d -serine’s functions in nonmammals are unclear. Here, we characterized d -serine–dependent vesicle release from the epidermis during metamorphosis of the tunicate Ciona . d -Serine leads to the formation of a pocket that facilitates the arrival of migrating tissue during tail regression. NMDAR is the receptor of d -serine in the formation of the epidermal pocket. The epidermal pocket is formed by the release of epidermal vesicles’ content mediated by d -serine/NMDAR. This mechanism is similar to observations of keratinocyte vesicle exocytosis in mammalian skin. Our findings provide a better understanding of the maintenance of epidermal homeostasis in animals and contribute to further evolutionary perspectives of d -amino acid function among metazoans.