Abstracts - Society for Developmental Biology

151
Program/Abstract # 456
Thoracic primary afferents bundle in segmentally distinct patterns during longitudinal extension in the embryonic
avian spinal cord
Ezerman, Elizabeth B.; Forehand, Cynthia, University of Vermont, Burlington, United States
As primary afferents grow into the spinal cord, they extend rostrally and caudally across multiple levels before entering the
grey matter to make segmental connections. We have asked whether the primary afferent projections from different
thoracic segmental levels of the chicken embryo intermingle as they extend longitudinally or remain in separate bundles.
Specifically, do the rostral projections from separate levels bundle together or do all the rostral projections from a single
segment bundle together and remain separate from those of other segments? How do the caudally projecting axons from a
rostral segment relate to the rostrally projecting axons of a caudal segment? What happens at the dorsal root entry zone
(DREZ) where entering fibers encounter those extending longitudinally from other segments? To investigate these
questions, we have used several colors of fluorescent dextran amines to label sequential spinal nerves (SPN) or ganglia
(DRGs). Distinct segmental (color) domains are seen some distance from the DREZ when adjacent segments are labeled.
Closer to the DREZ, there is apparent intermingling of fibers. When projections from two ganglia are labeled and the fiber
associations examined rostral to both ganglia, the rostral projections from the more rostral ganglion reside in a more
ventrolateral position. Conversely, examination of the caudal projections caudal to both ganglia shows that the caudal
projections of the more rostral ganglion are dorsomedial within the bundle. There is intermingling of fibers entering at a
DREZ with both rostrally and caudally projecting axons running longitudinally through the DREZ.
Program/Abstract # 457
Role of zebrafish Vangl2, a Wnt/Planar Cell Polarity pathway component, in cell behaviors underlying
convergence and extension gastrulation movements
Roszko, Isabelle, Washington University School of Medicine, St. Louis, United States; Jessen, Jason R (Vanderbilt
University, Nashville, U.S.A.); Sepich, Diane; Solnica-Krezel, Lilianna (Washington University School of Medicine, St
Louis, United States)
Initially discovered in Drosophila, where it is required for the organization of planar epithelial polarity, the PCP pathway
is evolutionarily conserved in vertebrates. In contrast to its well-described function in the relatively static Drosophila
epithelia, during vertebrate gastrulation, Wnt/PCP pathway is required for the regulation of the highly dynamic
mesenchymal cells behavior. However, how Wnt/PCP pathway functions in this dynamic context remains a challenging
open question. Zebrafish embryos carrying mutations in core PCP genes present characteristic phenotypes with shorter and
wider body axes, a consequence of perturbed convergence and extension movements. During zebrafish gastrulation cell
behaviors change in a stage and domain specific manner. From mid- to late gastrulation stages, mesodermal cell behavior
changes from slow dorsal convergence of individual cells to fast convergence of tightly packed and highly polarized cells.
In the zebrafish Wnt/PCP mutant trilobite, carrying a mutation in the vangl2 gene, the slow dorsal migration of
mesodermal cells is normal. At late gastrulation, mutant cells fail to elongate and their movement is slow and less effective.
We show that Vangl2 protein is recruited at the cell membrane at a specific time during gastrulation, correlating with
modification of cell behavior. Interestingly, our cell behavioral analysis shows that the transition in cell behavior is a
complex process with two independent steps: the cell shape modification and the cell body alignment along the embryonic
axes.
Program/Abstract # 458
The function of Sox11 in neurogenesis
Jin, Jing, Georgetown University, Washington, United States; Kubiak, Jeffrey (University of Pennsylvania, Philadelphia,
United States); Casey, Elena (Georgetown University, Washington, United States)
Sox proteins comprise a sub-family of transcription factors that contain an HMG (high mobility goup) DNA-binding
domain. They have various roles during development, including in chondrogenesis, sex determination and neural
development. Based on the amino acid sequence similarity of the HMG domains, Sox proteins are divided into groups A-
H. Sox11 belongs to the SoxC group of HMG-box transcription factors and recent studies have indicated that the SoxC
group factors function downstream of the proneural bHLH proteins and are necessary for neuronal maturation in the chick
spinal cord. To investigate the role of Sox11 in primary neurogenesis, we analyzed the result of loss-of -Sox11 function in
the frog Xenopus laevis. These studies reveal that loss of Sox11 function decreases the expression of proneural genes and
markers of mature neurons and slightly increases that of neural progenitor markers. Thus Sox11 is required for neuronal
maturation but may function upstream of the proneural proteins. With this information, we will investigate how the level of
Sox11 is controlled such that a population of neural progenitors is maintained for later development and only a subset of
cells differentiate during primary neurogenesis.