Congress Abstracts - Society for Developmental Biology

ontogeny. The typical condition for amniotes is to form outgrowths from the medial sides of the embryonic maxillary prominences
called palatal shelves. In mammals, the shelves fuse in the midline and form a bony hard palate that completely separates the nasal and
oral cavities. In birds and squamates, palatal shelves develop on the lateral sides of the oral roof but remain unfused, leaving a natural
cleft. In our study, we conclusively excluded the presence of vestigial palatal shelves at any time during the ontogeny of the
craniofacial complex in the turtle (Emydura subglobosa). Furthermore, through comparative analysis of avian and testudine
craniofacial gene expression patterns, we have identified a distinct lack of mesenchymal Bone Morphogenetic Protein 2 (BMP2)
expression in the maxillary prominences of E. subglobosa, a protein that is required for proliferation in the face. This lack of
expression was in turn correlated with a lack of proliferation increase expected in the putative palatal shelf outgrowth region when
compared to chicken embryos. In previous work we showed that when BMP signaling is blocked in the chicken embryo maxillary
prominence, a complete loss of palatal shelves occurs. We propose that the absence of BMP expression in the maxillary prominences
is associated with the lack of proliferation and this contributes to palatal shelf loss in turtles. JA is a recipient of an NIH F32 award,
the work was funded by an NSERC operating grant to JMR.
Program/Abstract # 287
Expression timing of Gdf11 reveals positional diversity of the hindlimb in vertebrates
Suzuki, Takayuki; Matsubara, Yoshiyuki (Nagoya University, Japan); Hattori, Ayumi; Ogura, Toshihiko (Tohoku University, Japan);
Se-Jin, Lee (Johns Hopkins Univ, USA); Kuroiwa, Atsushi (Nagoya University, Japan)
Previously, we have reported that Tbx5/Tbx4 specified wing/leg identity in the chick, and they were necessary and sufficient for limb
initiation. In this research, we were looking for upstream molecule of Tbx5/Tbx4. We found that GDF11 could control Tbx4 and Pitx1
expression in the chick lateral plate mesoderm (LPM). Gdf11 knockout mice show homeotic transformation of rostral bone to caudal
bone, including posterior shift of hindlimb position. We studied expression pattern of Gdf11 in the chick embryos. Gdf11 expression
starts suddenly from 10 somite stage at presomitic mesoderm (PSM). After implantation of bead soaked with GDF11, ectopic Pitx1
and Tbx4 expression were induced, compared to inhibition of Tbx5 expression. Further, when we co-implanted FGF8 expressing cells
with GDF11, only Tbx4 was induced in extra limb bud. This extra limb had leg type structure morphologically. We also found that
ALK4 receptor signaling is involved in GDF11 signaling at LPM by mouse whole embryo culture. We conclude that expression
timing of Gdf11 at PSM determines hindlimb position through Pitx1 and Tbx4 expression at LPM. In this conference, we will also
show expression timing of Gdf11 in several tetrapod species and discuss how leg field starts to develop in vertebrates.
Program/Abstract # 288
The participation of Wnt/Ca+ signaling and the Wnt antagonists DKK and SFRP in digit formation during limb development.
Farrera Hernandez, Alejandro ; Bustamante, Marcia; Flores-Hernández, Erick; Robles-Flores, Martha; Orozco-Hoyuela, Gabriel;
Chimal-Monroy, Jesús (UNAM, Mexico)
During limb embryogenesis, mesenchymal cells condense to give rise to chondrogenic blastema that prefigures the skeletal elements.
Limb chondrogenesis begins once Sox9 is expressed, promoting the formation of precartilage condensations and the subsequent
differentiation. It is known that WNT/β-catenin induces proliferation in the distal zone of the limb and inhibits chondrogenesis.
However, has been proposed that the non-canonical Wnt pathways oppose Wnt/β-catenin pathway. On the other hand, albeit Wnt5a
promotes to Sox9 expression and chondrogenesis, in vitro promotes by stimulating calcium signaling by CAMKII and NFAT
activation, its role in limb development is poor known. The aim of this work was if Wnt/Ca+ participate in the Digit Crescent (DC),
for this purpose, we determine the presence of intracellular calcium with FURA 2AM. Results showed calcium staining near the DC.
To see differences in Wnt signaling, we implanted presoaked beads with antagonists and put them in the tip of the digits, we used two
types of Wnt antagonist; DKK1, a specific Wnt/β-catenin antagonist and SFRP1 a general Wnt antagonist. In both treatments we
observed absence of phalanges by cartilage staining; also the treatment with the NFAT inhibitor 11R-VIVIT blocks the
chondrogenesis at the distal zone of the limb, reducing the size of phalanges or with the complete loss of the cartilage. We observed
differences of Sox9 expression between both WNT antagonists; while Dkk1 increased Sox9 expression in the first 12 hours, SFRP1
reduce Sox9 expression in the first 8 hours. This data suggest that Wnt/Ca+ signaling may participate in DC chondrogenesis. Support:
CONACyT grant 53484 and 168642, DGAPA-UNAM grant IN214511 and IN220808.
Program/Abstract # 289
The Origin of the Thumb Patterning System
Tanaka, Mikiko; Onimaru, Koh (Tokyo Institute of Technology, Japan)
Evolution of gene regulatory networks is regarded as a driving force of morphological evolution. Recent molecular studies for
vertebrate fin-to-limb transformation suggests that autopod-related gene regulation predate the acquisition of autopod structures.
However, the mechanism of how gene regulatory changes led to fin-to-limb transformations remains unknown. Here, we examined fin
development of a dogfish Scyliorhinus canicula, and provide evidence suggesting that anterior-posterior patterning changes in fins
could have triggered anatomical transformations such as digit acquisition and reduction of fin radials. Anterior radials of S. canicula
fins expressed a gene set shared with the anterior elements of mouse limbs such as digit I, radius and deltoid process. Nevertheless, a
homologous element of Gli3 anterior limb enhancer from chondrichthyan drove reporter expression throughout the limb buds of chick
embryos. Thus the anterior-posterior patterning system may have been modified through alteration of the cis-element of Gli3,
resulting in transformation of anterior fin radials into the digit I, radius, and deltoid process of tetrapod limbs.
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