Two growth factors cooperate to maintain a pool of neuron-generating stem cells in the brain, according to a study by researchers at the University of Medicine and Dentistry of New Jersey. Numerous soluble proteins and receptors help to maintain neural stem cells’ (NSCs) in the central nervous system (CNS). Insulin-like growth factors (IGF-I and IGF-II) are essential for the growth and development of the CNS. But although they are abundant in the brain and CSF, it was not clear whether they are required by NSCs. Steven Levison, Teresa Wood and colleagues now show that IGF-I and –II cooperate to maintain NSC levels and the NSCs’ ability to self-renew. IGF-I maintains NSC numbers by promoting cell division, whereas IGF-II drives the expression of proteins essential for NSC self-renewal and “stemness” (via the insulin receptor).