Inhibition of cell death results in hyperganglionosis: implications for enteric nervous system development

The enteric nervous system (ENS) is derived from vagal and sacral neural crest cells (NCC) that delaminate from the neural tube and undergo extensive migration and proliferation in order to colonize the entire length of the gut and differentiate into many millions of neurons and glial cells. Although apoptotic programmed cell death is an essential physiological process during development of the majority of the vertebrate nervous system, apoptosis within early ENS development has not been comprehensively investigated. The aim of this study was to determine the presence and extent of apoptosis within the vagal NCC population that gives rise to most of the ENS in the chick embryo. We demonstrated that apoptotic cells, as shown by terminal deoxynucleotidyl transferase biotin-dUTP nick end labelling and active caspase-3 immunoreactivity, are present within an electroporated green fluorescent protein (GFP) and human natural killer-1 (HNK-1) immunopositive NCC population migrating from the vagal region of the neural tube to the developing foregut. Inhibition of caspase activity in vagal NCC, by electroporation with a dominant-negative form of caspase-9, increased the number of vagal NCC available for ENS formation, as shown by 3-dimensional reconstruction of serial GFP or HNK-1 labelled sections, and resulted in hyperganglionosis within the proximal foregut, as shown by NADPH-diaphorase whole gut staining. These findings suggest that apoptotic cell death may be a normal process within the precursor pool of pre-enteric NCC that migrates to the gut, and as such it may play a role in the control of ENS formation.