Abstracts - Society for Developmental Biology

102
Cdx1 peaks in the distal colon and Cdx2 in the proximal cecum. Moreover, Cdx1 expression is graded along the cryptvillus
axis, with more abundant protein found in the crypts, which house stem cells, and diminishing towards the
differentiated cells in the villi. Cdx2 is expressed uniformly along this crypt-villusaxis, but is differentially phosphorylated.
The functional consequences and mechanisms of regulation of these different expression domains of the Cdx proteins
remain unknown. Herein, we demonstrate that Cdx2 driven by Cdx1 regulatory elements cannot functionally compensate
for loss of endogenous Cdx2. Furthermore, we show evidence that Cdx2 cannot functionally compensate for Cdx1 in the
context ofintestinal homeostasis in the distal colon. This study provides novel in vivo evidence that Cdx1 and Cdx2 have
context dependent functional specificity.
Program/Abstract # 310
Cdx and FGF interactions establish a molecular switch for posterior nervous system specification
Hayward, Albert; Skromne, Isaac, University of Miami, Coral Gables, FL, United States
During development, neural cells can respond to the same signaling factors in remarkably different ways depending on
their molecular context or competence. What determines a cell’s competence and its specific response to signaling inputs
remains unknown. We have investigated issues of neural competence in a simple binary-decision system: the specification
of caudal neural plate cells to hindbrain or spinal cord fates. Hindbrain and spinal cord specification depend on the
signaling activity of FGFs and the caudally restricted transcriptional activity of Cdx. We have examined how molecular
context, presence or absence of Cdx, allows prospective hindbrain cells (Cdx negative) and prospective spinal cord cells
(Cdx positive) to respond in distinctive ways to FGF signaling by activating particular developmental programs in a cellspecific
fashion. Here we show that a network of FGF and Cdx interactions specify and pattern the spinal cord. Using loss
and gain of function strategies, we show that induction of spinal cord fates requires Cdx independently of FGF. However,
subsequent maintenance of spinalcord fates by Cdx requires FGF activity. Similarly, induction of patterning genes (hox)
expression only requires Cdx, but their maintenance requires Cdx and FGF activities. The maintenance of spinal cord
specification and patterning information involves the maintenance of Cdx auto-regulation by FGF. We propose that Cdx
and FGF interactions establish a molecular switch that stabilizes the induction of spinal cord fates and promotes the
patterning of posterior nervous system.
Program/Abstract # 311
Interneuron specification in zebrafish spinal cord
Hilinski, William, SUNY Upstate Medical University, Syracuse, United States; England, Samantha; Jager, Sarah;
Rodriguez-Larrain, Gisella; Lewis, Kate (Syracuse Unviersity, Syracuse, NY, United States)
Most of the neurons in the vertebrate Central Nervous System (CNS) are interneurons and interneurons function in almost
all neuronal circuits and behaviors. However, we still know very little about how specific interneurons with particular
physiological and functional characteristics develop and form functional neuronal circuitry. All of the evidence so far
suggests that the properties of distinct spinal cord interneurons are determined by the transcription factors that the cells
express as they become post-mitotic and start to differentiate. However, in many cases, it is still unclear which
transcription factors specify particular interneuron properties. We also do not know the full complement of transcription
factor sexpressed by any population of spinal interneurons in any vertebrate. To address these critical gaps in our
knowledge we are using and developing several techniques. For example, we are Fluorescence Activated Cell-Sorting
(FACS) and expression profiling specific spinal cord interneuron populations using transgenic zebrafish lines where these
cell types are labeled with fluorescent proteins. This enables us to identify all of the transcriptionfactors expressed by these
different interneuron populations. Furthermore, we are comparing and contrasting expression profiles of interneurons with
similar and different axon trajectories and/or neurotransmitter phenotypes to identify transcriptions factors that are good
candidates for specifying these functional properties. We will then test the functions of these transcription factors using
mutant lines, morpholino oligonucleotides, and dominant-negative constructs. One interneuron population that we are
particularly interested in is V0v spinalcord interneurons. These interneurons are located in the ventral spinal cord and are
part of the CNS circuitry that controls locomotion. They can be identified by their expression of the transcription factor
Evx1, which, within the spinal cord, is uniquely expressed by these interneurons. We are currently identifying all of the
transcription factors expressed by V0v interneurons and inparticular we are examining the functions of different
transcription factors inspecifying V0v axonal and neurotransmitter phenotypes.
Program/Abstract # 312
Specific requirement of floor plate Shh in spinal cord development
Kwanha, Yu, UMDNJ-Piscataway Neuroscience and Cell Biology, Piscataway, United States; Matise, Michael
(Piscataway, NJ, United States)