The role of floor plate contact in the elaboration of contralateral commissural projections within the embryonic mouse spinal cord.
In vertebrate embryos, commissural axons extend toward and across the floor plate (FP), an intermediate target at the ventral midline (VM) of the spinal cord. After decussating, many commissural axons turn into the longitudinal plane and elaborate diverse projections. FP contact is thought to alter the responsiveness of these axons so that they can exit the FP and adopt new trajectories. However, a requirement for the FP in shaping contralateral commissural projections has not been established in higher vertebrates. Here we further analyze to what extent FP contact is necessary for the elaboration of decussated commissural projections both in cultured, FP-excised spinal cord preparations and in gli2-deficient mice, which lack a FP. In FP-lacking spinal cords, we observe a large number of appropriately projecting contralateral commissural projections in vivo and in vitro. Surprisingly, even though gli2 mutants lack a FP, slit1-3 mRNA and their receptors (Robo1/2) are expressed in a wild-type-like manner. In addition, blocking Robo-Slit interactions in FP-lacking spinal cord explants prevents commissural axons from leaving the VM and turning longitudinally. Thus, compared to FP contact, Slit-Robo interactions are more critical for driving commissural axons out of the VM and facilitating the elaboration of a subset of contralateral commissural projections.
Kadison
Stephanie R
SR
Department of Pathology and Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Kennedy Center Rm. 624, 1410 Pelham Parkway South, Bronx, NY 10461, USA. skadison@aecom.yu.edu
Murakami
Fujio
F
Matise
Michael P
MP
Kaprielian
Zaven
Z
D000818:Animals; D001369:Axons / Q000378:metabolism / Q000502:physiology; D046149:Embryo Culture Techniques; D005260:Female; D051741:Kruppel-Like Transcription Factors / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D009434:Neural Pathways / Q000502:physiology; D013116:Spinal Cord / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D000071676:Zinc Finger Protein GLI1
C498520:Gli1 protein, mouse; D051741:Kruppel-Like Transcription Factors; D000071676:Zinc Finger Protein GLI1