A subpopulation of neural crest termed the cardiac neural crest is required
in avian embryos to initiate reorganization of the outflow tract of the de
veloping cardiovascular system. In mammalian embryos, it has not been previ
ously experimentally possible to study the long-term fate of this populatio
n, although there is strong inference that a similar population exists and
is perturbed in a number of genetic and teratogenic contexts. We have emplo
yed a two-component genetic system based on Cre/lox recombination to label
indelibly the entire mouse neural crest population at the time of its forma
tion, and to detect it at any time thereafter. Labeled cells are detected t
hroughout gestation and in postnatal stages in major tissues that are known
or predicted to be derived from neural crest. Labeling is highly specific
and highly efficient. In the region of the heart, neural-crest-derived cell
s surround the pharyngeal arch arteries from the time of their formation an
d undergo an altered distribution coincident with the reorganization of the
se vessels. Labeled cells populate the aorticopulmonary septum and conotrun
cal cushions prior to and during overt septation of the outflow tract, and
surround the thymus and thyroid as these organs form. Neural-crest-derived
mesenchymal cells are abundantly distributed in midgestation (E9.5-12.5), a
nd adult derivatives of the third, fourth and sixth pharyngeal arch arterie
s retain a substantial contribution of labeled cells. However, the populati
on of neural-crest-derived cells that infiltrates the conotruncus and which
surrounds the noncardiac pharyngeal organs is either overgrown or selectiv
ely eliminated as development proceeds, resulting for these tissues in a mo
dest to marginal contribution in late fetal and postnatal life.