Within the developing neocortex, multiple progenitor cell types contribute to neuronal production, and the properties and relative abundance of these populations help to define the extent of neocortical growth. As well as apically localised radial glial cells (RGCs) that comprise the stem cell compartment, various populations of basal progenitors (BPs) exist - including basal RGCs, with both self-renewal and proliferative capacity, and more restricted progenitors. The stem cell-like properties of RGCs are linked to the fact that these cells are connected to the basal lamina, from which they receive proliferative signals via integrins. Now, Denise Stenzel et al. investigate in rodents the role of integrin αvβ3 in regulating the proliferative capacity of BPs (p. 795). They find that activation of this integrin induces BP proliferation both in hemisphere culture and in vivo, promoting proliferative division at the expense of neurogenic division. Moreover, they show that the αvβ3 ligand thyroid hormone also regulates BP proliferation via this integrin - providing pro-proliferative signals to progenitor cells that are not connected to the basal lamina.