Aplysia mollusk-derived growth factor is a mitogen with adenosine deaminase activity and is expressed in the developing central nervous system

Mollusk-derived growth factor (MDGF), the first growth factor to be characterized in Aplysia, was purified and characterized and has both adenosine deaminase activity and stimulates cell proliferation in vitro. MDGF is structurally related to a new subfamily of adenosine deaminase-related growth factors that require enzymatic activity to stimulate cell proliferation, a unique property of known growth factors. We examined the expression of MDGF protein in the CNS since MDGF mRNA increased in the developing CNS, and recent data suggest that inosine is involved in neuronal reorganization and restoration of essential circuitry after CNS injury. MDGF levels transiently increased during embryonic and post-metamorphic development and in the developing CNS, but was undetectable in adult CNS. No effects on morphology or neurite extension of adult Aplysia neurons were observed.