Insulin-like growth factor actions during development of neural stem cells and progenitors in the central nervous system

Insulin‐like growth factor‐I (IGF‐I) plays a key role in normal development. Recent studies show that IGF‐I exerts a wide variety actions in the central nervous system during development as well as in adulthood. This report reviews recent developments on IGF‐I actions and its mechanisms in the central nervous system, with a focus on its actions during the development of neural stem cells and progenitors. Available data strongly indicate that IGF‐I shortens the length of the cell cycle in neuron progenitors during embryonic life and has an influence on the growth of all neural cell types. The phosphatidylinositol‐3 kinase/Akt and mitogen‐activated protein kinase pathways seem to be the predominant mediators of IGF‐I–stimulated neural cell proliferation and survival. IGF‐I actions, however, likely depend on cell type, developmental stage, and microenvironmental milieu. © 2005 Wiley‐Liss, Inc.