Congress Abstracts - Society for Developmental Biology

Repulsive guidance molecules (RGM) are ligands for Neogenin receptor which play a number of roles during nervous system
development, including neural tube closure; neuronal and neural crest cell differentiation and axon guidance. RGM molecules were
also implicated in BMP signaling, which regulates a variety of processes during development. Given that new roles for Neogenin
outside the nervous system are recently emerging, and that BMP signaling controls the development of neural as well as non-neural
tissues, we were wondering to which extent RGM molecules may control non-neural developmental processes. Chicken embryos were
used to investigate possible new biological roles for RGM genes in these processes. The current edition of the chicken genome
predicts the existence of only two RGM genes (among the four members of the family) in this species: RGMa and RGMb. The
expression pattern of RGMa and RGMb was determined by in situ hibridization, from gastrulation (HH3) to organogenesis (HH27)
stages of chicken embryonic development. Our data confirmed RGMa expression in the neural plate and neural tube, and RGMb
expression in differentiating neurons and cranial and dorsal root ganglia. New expression patterns were observed for RGMb in the
notochord. Moreover, both RGMa and RGMb were expressed in the somite, with RGMa predominantly labeling muscle precursor and
muscle stem cells and RGMb labeling differentiating muscle. Therefore, our expression pattern data suggested so far unknown roles
for RGM molecules in notochord, somite and skeletal muscle development.
Program/Abstract # 139
The transcription factor cScratch2 is an early marker for post-mitotic neural precursors
Vieceli, Felipe; Kanno, Tatiane (Universidade de São Paulo, Brazil); Simões-Costa, Marcos; Bronner, Marianne (California Institute
of Technology, USA); Yan, Irene (Universidade de São Paulo, Brazil)
The Scratch (Scrt) genes code zinc-finger transcription factors that participate in neural development. Functional studies in different
animal models indicate that Scrt promotes survival of neural cells. In addition, gain-of-function studies in the mouse embryonic cortex
suggest a role in neuronal migration. In this work, we have investigated the embryonic expression of the chicken Scrt2 ortholog
(cScrt2) and its relationship with other neural factors. Sequencing of RACE-PCR products from HH19 and HH24 libraries suggests
the existence of at least four alternate spliced transcripts. In situ hybridization in whole mounts using a probe that should detect all the
identified transcripts show that cScrt2 is first expressed in few cells of the hindbrain and in the nasal placode by HH15, and later in the
hindbrain, spinal cord, cranial ganglia and dorsal root ganglia (DRG). Double labeling in sections indicate that cScrt2-positive cells in
the spinal cord are post-mitotic and express NeuroM, and that cScrt2 is coexpressed with Islet1 in motoneurons and DRG neurons.
Our results suggest that cScrt2 is one of the first genes expressed after cell cycle arrest of spinal cord and DRG neurons, and may act
in conjunction with NeuroM. In silico analysis of genomic sequences to identify potential regulatory non-coding regions revealed the
presence of a conserved intronic element in the cScrt2 locus that contains putative transcription factors binding sites. Additionally, in
silico search for post-translationally regulated sites identified candidate phosphorylation targets in the predicted aminoacid sequence.
These data raise new questions on the different levels of regulation acting on the Scrt2 gene in vertebrates.
Program/Abstract # 140
Cell-type specific analysis of chromatin modifications at the Drosophila shavenbaby gene
Preger-Ben Noon, Ella; Preger-Ben; Lemire, Andrew; Stern, David (Howard Hughes Medical Institute, USA)
Pattern formation involves the integration of multiple inputs from gene regulatory networks through cis-regulatory regions, leading to
cell-type specific gene expression. Many developmental genes possess large regulatory regions composed of many individual
enhancer modules. Each of these modules contributes some features of the expression pattern which together coordinate the overall
pattern. Such modularity allows the formation of complex gene expression patterns as well as the evolution of these patterns. The
drosophila shavenbaby (svb) gene provides a superb model for studying cis-regulatory structure, function, and evolution. The svb gene
encodes a transcription factor that regulates the development of cuticular hair-like projections called trichomes. Svb is expressed in a
complex pattern in the embryonic ectoderm and acts to switch epidermal cells between naked cuticle and trichome bearing cells. At
least six enhancer modules located in the cis-regulatory region of svb together recapitulate the entire svb embryonic expression
pattern. This collection of individual svb enhancers, each regulated in a cell-specific manner, provides an opportunity to examine how
varied transcriptional inputs regulate chromatin structure. To generate a comprehensive view of the regulatory landscape of the svb
gene we have used a new method of cell-type specific analysis of chromatin states. Briefly, embryonic nuclei expressing fluorescent
reporters under the control of different svb enhancers are sorted and histone modification patterns at the svb loci are determined by
ChIP-seq. Here we report the current state of our analysis.
Program/Abstract # 141
Zac1 controls cell cycle exit of neural progenitors through direct regulation of cyclin-dependent kinase inhibitor expression
along the entire rostrocaudal axis of the developing central nervous system
Rraklli, Vilma (Ludwig Institute for Cancer Research, Sweden)
The central nervous system (CNS) is characterized by a sophisticated architecture where different cell types support neuronal
functions. During CNS development neurons, astrocytes and oligodendrocytes are generated from a pool of neural progenitors located
in the ventricular zone (VZ) and subventricular zone (SVZ). Proper development and functionality of CNS is achieved via regulatory
mechanisms that dictate when neural progenitors should proliferate or exit the cell cycle. Despite the crucial importance of
coordination between cell cycle exit and differentiation, such mechanisms remain poorly understood. Here we show that the zinc
finger transcription factor Zac1 regulates cell cycle exit through control of expression of cyclin-dependent kinase inhibitors (CKIs).
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