In the developing neocortex, Bcl11b is strongly expressed across layer V in subcerebral projection neurons as well as weakly in layer VI corticothalamic neurons (Arlotta et al., 2005), and specifies their respective laminar identities. Layer V subcerebral neurons are early-born neurons (E12.5-E14.5) which project to targets caudal to the cerebrum, including the brainstem and spinal cord (Killackey et al., 1989; Glickstein et al., 1985; Molnár and Cheung, 2006; Wise and Jones, 1977). Bcl11b deletion affects the later stages of subcerebral axonal outgrowth and refinement, including fasciculation, pathfinding and pruning. In particular, Bcl11b is haploinsufficient for axonal pruning in corticospinal neurons, a subtype of subcerebral neurons that project to the spinal cord (Arlotta et al., 2005). Similarly, in the striatum, Bcl11b is exclusively expressed in postmitotic medium spiny neurons (MSNs) and is required for their maturation, including the expression of MSN markers and organization into patches (Arlotta et al., 2008).
