THE DELAYED ENTRY OF THORACIC NEURAL CREST CELLS INTO THE DORSOLATERAL PATH IS A CONSEQUENCE OF THE LATE EMIGRATION OF MELANOGENIC NEURAL CREST CELLS FROM THE NEURAL-TUBE
Mv. Reedy et al., THE DELAYED ENTRY OF THORACIC NEURAL CREST CELLS INTO THE DORSOLATERAL PATH IS A CONSEQUENCE OF THE LATE EMIGRATION OF MELANOGENIC NEURAL CREST CELLS FROM THE NEURAL-TUBE, Developmental biology (Print), 200(2), 1998, pp. 234-246
Neural crest cells migrate along two pathways in the trunk: the ventra
l path, between the neural tube and somite, and the dorsolateral path,
between the somite and overlying ectoderm. In avian embryos, ventral
migration precedes dorsolateral migration by nearly 24 h, and the onse
t of dorsolateral migration coincides with the cessation of ventral mi
gration. Neural crest cells in the ventral path differentiate predomin
antly as neurons and glial cells of the peripheral nervous system, whe
reas those in the dorsolateral path give rise to the melanocytes of th
e skin. Thus, early- and late-migrating neural crest cells exhibit uni
que morphogenetic behaviors and give rise to different subsets of neur
al crest derivatives. Here we present evidence that these differences
reflect the appearance of specified melanocyte precursors, or melanobl
asts, from late- but not early-migrating neural crest cells. We demons
trate that serum from Smyth line (SL) chickens specifically immunolabe
ls melanocyte precursors, or melanoblasts. Using SL serum as a marker,
we first detect melanoblasts immediately dorsal and lateral to the ne
ural tube beginning at stage 18, which is prior to the onset of dorsol
ateral migration. At later stages every neural crest cell in the dorso
lateral path is SL-positive, demonstrating that only melanoblasts migr
ate dorsolaterally. Thus, melanoblast specification precedes dorsolate
ral migration, and only melanoblasts migrate dorsolaterally at the tho
racic level. Together with previous work (Erickson, C. A., and Goins,
T. L., Development 121, 915-924, 1995), these data argue that specific
ation as a melanoblast is a prerequisite for dorsolateral migration. T
his conclusion suggested that the delay in dorsolateral migration (rel
ative to ventral migration) may reflect a delay in the emigration of m
elanogenic neural crest cells from the neural tube. Several experiment
s support this hypothesis. There are no melanoblasts in the ventral pa
th, as revealed by the absence of SL-positive cells in the ventral pat
h, and neural crest cells isolated from the ventral path do not give r
ise to melanocytes when explanted in culture, suggesting that early, v
entrally migrating neural crest cells are limited in their ability to
differentiate as melanocytes. Similarly, neural crest cells that emigr
ate from the neural tube in vitro during the first 6 h fail to give ri
se to any melanocytes or SL-positive melanoblasts, whereas neural cres
t cells that emigrate at progressively later times show a dramatic inc
rease in melanogenesis under identical culture conditions. Thus, the t
iming of dorsolateral migration at the thoracic level is ultimately co
ntrolled by the late emigration of melanogenic neural crest cells from
the neural tube. (C) 1998 Academic Press.