Predecessor Neurons in Cortical Development

Predecessor cells, a type of embryonic neuron, are unique to humans. In humans, a transient population of large, bipolar neurons has been observed to emerge under the pial surface of the ventro-lateral cerebral wall at the end of the 1st gestational month, before completion of the neural tube closure and before onset of neurogenesis in the proliferative ventricular and subventricular zones of the dorsal telencephalon (Bystron et al., 2006). They are immunoreactive to neuron specific beta III tubulin (TU20) and transcription factor Tbr1, but are Reelin negative, and develop long horizontal processes forming an extensive network under the surface of the human forebrain primordium. The function of predecessor cells is not known but a working hypothesis is that as a transient populations, they may involved in determining the number of functional radial units in the large primate cerebral neocortex. The predecessor neurons, as defined by their position, as well as by morphological and biochemical characteristics, has not been observed in the early embryonic forebrain of any other species examined so far, including rodents and carnivores. However, studies have yet to be carried out in nonhuman primates, so it is currently unclear whether predecessor calls are uniuqe to humans or to a more inclusive primate group.