Sm. Leber et Jr. Sanes, MIGRATORY PATHS OF NEURONS AND GLIA IN THE EMBRYONIC CHICK SPINAL-CORD, The Journal of neuroscience, 15(2), 1995, pp. 1236-1248
To study the migration of chick spinal cord neurons, we labeled indivi
dual cells in the ventricular zone with recombinant retroviruses, then
identified their progeny histochemically. First, we analyzed cell mix
ing in the ventricular zone. Some clones labeled at early neural tube
stages spread widely along both the dorsoventral and rostrocaudal axes
. However, clones labeled later were confined to narrow domains along
both axes. These results imply that displacement of cells within the v
entricular zone becomes progressively restricted. Second, we studied t
he migration of cells out of the ventricular zone by infecting embryos
at a fixed stage and varying the time of analysis. At first, most clo
nes consisted of radial arrays of cells, suggesting that the initial m
igration is predominantly radial. In many clones, however, neurons tur
ned orthogonally from parental radial arrays and migrated along the pa
th of circumferentially oriented axons. By hatching, clonally related
cells in the gray matter were usually distributed in narrow transverse
slabs, but some white matter glial cells had migrated longitudinally
for up to several segments. We conclude that the dispersal of clonally
related cells results from(1) early mixing of progenitors within the
neural tube; (2) radial stacking of progeny in the ventricular zone; (
3) migration of progeny from the ventricular zone in spoke-like routes
; (4) circumferential migration of some neurons along axons; (5) short
-distance dispersal of differentiating neurons; and (6) a late, longit
udinal migration of glia through white matter tracts. Finally, we show
that floor plate cells differ from other spinal cord cells in both th
eir lineage and migration patterns.