Congress Abstracts - Society for Developmental Biology

Program/Abstract # 283
Your Inner Inner Fish: Analysis of Pharyngeal Segmentation in Vertebrates
Shone, Victoria; Graham, Anthony (MRC Centre for Developmental Neurobiology, UK)
Pharyngeal arches are bulges found on the lateral surface of the head of vertebrate embryos. They form a segmented series that the
pharynx is built on, and a complex array of tissues and signals are involved in their formation. Arches become segmented when
endodermal pharyngeal pouches develop and elongate along a dorsoventral axis, eventually fusing with the ectodermal pharyngeal
clefts. We aim to determine if a Hox code present within the endoderm is responsible for regionalization of the pouches. We also aim
to characterise the interaction between ectoderm and endoderm when they make contact, and to analyse the differences in pouch
morphology within and across different vertebrate species. To analyse this interaction, ectoderm and endoderm were separately
labelled using various methods including fluorescent immunohistochemistry, CCFSE labelling, and lineage tracing in mouse and
zebrafish reporter lines. This work has revealed how these tissues interact at each of the pouches, generating the unique morphology of
each pouch which is maintained as they mature. Another interesting feature within vertebrates is the varying number of pharyngeal
arches: lamprey have 9, sharks have 7 and chicks have 5. To elucidate how these arches were lost during vertebrate evolution, we have
used neuronal antibody labeling to determine where cranial nerve innervation has been lost and hence where the arches have been lost.
These results will be discussed.
Program/Abstract # 284
In vivo evidence for a novel and direct role of Cdx proteins in trunk neural crest cell development
Sanchez, Oraly; Pilon, Nicolas (UQAM, Montreal, PQ, Canada)
Cdx genes (Cdx1, Cdx2 and Cdx4) encode homeodomain transcription factors critical for development of the posterior chordate
embryo with notable well-known key roles in anterior-posterior (AP) patterning and axial elongation. Cdx members are expressed in
all three germ layers of the caudal embryo from e7.5 to e12.5. However, specific Cdx functions in the neurectoderm are still poorly
understood because of functional redundancy and early embryonic lethality. Moreover, although important emergent roles for Cdx
proteins in neural tube and neural crest formation have been described, it is still unknown whether these roles are tissue-autonomous
or not (via the mesoderm). To circumvent functional redundancy and early embryonic lethality as well as to address a direct role for
Cdx proteins in neural development, we have generated a conditional (Cre-dependent) pan-Cdx loss-of function mouse model
expressing a previously described Cdx dominant negative fusion protein (EnRCdx1; Sanchez-Ferras et al., JBC 2012) under the
control of the ROSA26 promoter. The efficacy of this approach has been validated by crossing our novel line, called R26R EnRCdx1/+ ,
with T-Cre Tg/+ mice. In agreement with the key Cdx role in mesodermal AP patterning as well as the dominant nature of EnRCdx1,
R26R EnRCdx1/+ ::T-Cre Tg/+ double transgenic mice display vertebral patterning defects as severe as those observed in Cdx compound
mutants. Most interestingly, directing expression of EnRCdx1 specifically in the dorsal neural tube and pre-migratory neural crest
cells using the Pax3pro-Cre line results in pigmentation defects that phenocopy those observed in Pax3 Sp/+ mutants. Taken together
with other data describing a direct and crucial regulation of a Pax3 neural crest enhancer by Cdx proteins, our work constitutes the
first in vivo demonstration for a direct role of Cdx proteins in trunk neural crest cell development.
Program/Abstract # 285
Endothelin Signaling Balances Identity of Neural Crest Cells in the First Pharyngeal Arch
Tavares, Andre Luiz Pasqu; Clouthier, David (Univ. of Colorado at Denver, USA)
Endothelin-1 (Edn1)-induced signaling of the endothelin-A receptor (Ednra) is crucial for dorsal-ventral (D-V) patterning of cranial
neural crest cells (CNCCs) within the mandibular pharyngeal arch. Targeted deletion of Edn1 or Ednra in mice causes perinatal
lethality due to severe craniofacial birth defects that include homeotic transformation of mandibular arch-derived structures into more
maxillary-like structures, indicating a loss of NCC identity. CNCCs express Ednra whereas Edn1 is derived from the overlying
ectoderm, core paraxial mesoderm and pouch endoderm. To define the pathways that establish a more dorsal/ ventral fate in the first
pharyngeal arch, we created transgenic mice containing a silent Edn1 expression cassette (CBA-Edn1). When Edn1 was overexpressed
in CNCCs (CBA-Edn1;Wnt1-Cre), the overexpression caused a homeotic transformation of maxillary structures into more
mandibular-like structures. This transformation was preceded by a proximal expansion of distal genes (Dlx3, Dlx5 and Hand2) and
disruption of proximal genes (Dlx2, Twist1, Pou3f3, Six1 and Eya1) in the first arch. We focused on Six1, as it plays roles in
vertebrate development, with mutations in Six1 and/or its partner Eya1 found in patients with branchio-oto-renal syndrome, a
developmental disorder that is characterized by hearing loss, branchial arch defects and renal anomalies. While Six1-null mouse
embryos have facial defects, deletion of one allele of Ednra partially rescued the defect (Six1 -/- ;Ednra +/- ). Together, our results suggest
that proximal first pharyngeal arch is competent to form either a mandible or a maxilla and that inductive/repressive signals that
include Six1 and Edn1 are responsible for driving CNCCs into either fate.
Program/Abstract # 286
Craniofacial Ontogeny in Turtles: putative role of bone morphogenetic proteins in the lack of palatal shelves
Abramyan, John; Leung, Kelvin; Richman, Joy (University of British Columbia, Canada)
Turtles are an enigmatic group of vertebrates whose unique skull morphology is still at the forefront of scientific discussion. While
turtles pass through a conserved stage of primary palate development found in all amniotes, they diverge during secondary palate
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