Congress Abstracts - Society for Developmental Biology

Program/Abstract # 375
Identification of Cell Motility Genes Specific to Primitive Myeloid Linieage in Xenopus laevis
Kenny, Alan; Jagpal, Amrita; Allbee, Andrew; Prewitt, Allison; Shifley, Emily; Zorn, Aaron (Cincinnati Children's Hospital, USA)
Vertebrate blood development occurs in 2 conserved spatially and temporally distinct waves: primitive and definitive hematopoiesis.
In Xenopus neurula and tail bud stages, spib-expressing primitive myeloid cells emerge in the anterior ventral blood islands (aVBI),
the equivalent of the mammalian yolk sac. Over time these cells later migrate throughout the embryo. Despite gains in understanding
myeloid development, an important question remains: what genes are induced specific to the primitive myeloid lineage allowing it to
differentiate and migrate. The aims of this research are to: (1) identify the genes from the developing myeloid lineage and (2)
determine the dynamic expression profiles of these genes during myeloid differentiation and migration. We examined expression of
selected genes from 3 anterior ventral explant microarray sets in relation to myeloid-specific expression through neurula and early
tailbud stages and compared their expression to spiba, a myeloid marker. We also used morpholino to generate aVBI-targeted spiba
loss-of-function and examined the loss-of-function effect on these genes’ expression by in situ. Compiled microarray experiments
identified 10 genes specifically expressed in the aVBI-derived myeloid cells, all of which are implicated in cell migration. Dorsaltargeted
Morpholino knockout of spib specifically in the foregut area produced a decrease in the expression of actin-binding proteins
coronin and cofilin consistent with them being downstream of myeloid-specific spiba transcriptional regulation. Together, these
results suggest a number of genes involved in cell motility including are specifically expressed in differentiating primitive myeloid
cells regulated by spiba.
Program/Abstract # 376
The Role of BMPs in Digit Number Regulation
Norrie, Jacqueline; Li, Qiang (University of Texas-Austin, USA); Bouldin, Courtney; Harfe, Brian (University of Florida, USA);
Vokes, Steven (University of Texas-Austin, USA)
Bone morphogenetic proteins (BMPs) are essential for many aspects of limb development including limb bud outgrowth, axial
specification, and skeletogenesis. The collective temporal roles of BMPs have been difficult to determine because there are multiple,
partially redundant ligands. To observe how and when BMPs regulate digit formation, we generated a mouse model that drives Creinducible
transcription of the BMP inhibitor Gremlin, allowing temporal regulation of BMPs. Activation of Gremlin throughout the
limb bud mesenchyme results in the generation of polydactylous hindlimbs and nearly absent forelimbs. By inhibiting BMPs at
various timepoints we demonstrate that they are essential for restricting digit number during an interval between E10 and E11. The
ectopic expression of Gremlin reduces but does not eliminate endogenous BMP signaling. This inhibition results in increased and
sustained Fgf and Shh activity. Our current efforts are focused on elucidating the role of BMP inhibition in regulating cell growth.
Program/Abstract # 377
Transient Inhibition of FGFR2b Signaling Leads to Irreversible Loss of Cellular Beta-Catenin Organization and Signaling in
AER During Mouse Limb Development
Danopoulos, Soula; Al Alam, Denise; Parsa, Sara; Tabatabai, Reza; Bellusci, Saverio (USC/CHLA, USA)
The vertebrate limbs develop through coordinated series of inductive, growth and patterning events. Fibroblast Growth Factor receptor
2b (FGFR2b) signaling controls the induction of the Apical Ectodermal Ridge (AER) but its putative roles in limb outgrowth and
patterning, as well as in AER morphology and cell behavior have remained unclear. We have investigated these roles through graded
and reversible expression of soluble dominant-negative FGFR2b molecules at various times during mouse limb development, using a
doxycycline/transactivator/ tet(O)-responsive system. Transient attenuation (≤24 hours) of FGFR2b signaling at E8.5, prior to limb
bud induction, leads mostly to the loss or truncation of proximal skeletal elements with less severe impact on distal elements.
Attenuation from E9.5 onwards, however, has an irreversible effect on the stability of the AER, resulting in a progressive loss of distal
limb skeletal elements. The primary consequences of FGFR2b attenuation is a transient loss of cell adhesion and down-regulation of
P63, beta 1-integrin and E-cadherin, and a permanent loss of cellular beta-catenin organization and WNT signaling within the AER.
Combined, these effects lead to the progressive transformation of the AER cells from pluristratified to squamous epithelial-like cells
within 24 hours of doxycycline administration. These findings show that FGFR2b signaling has critical stage-specific roles in
maintaining the AER during limb development.
Program/Abstract # 378
De-coupling the Hox-Shh-Fgf interaction reveals multiple inputs of Hox genes on pathways ensuring limb growth.
Sheth, Rushikesh; Grégoire, Damien; Dumouchel, Annie; Scotti, Martina; My Trang Pham, Jessica; Nemec, Stephen (Institut de
Recherches Cliniques de Montréal Canada); Bastida, Maria Félix; Ros, Marian (Instituto de Biomedicina y Biotecnología de
Cantabria (CSIC-UC-IDICAN) and University of Cantabria, Spain); Kmita, Marie (Institut de Recherches Cliniques de Montréal,
Canada)
One of the most intriguing questions in developmental biology is how organ growth and patterning are coordinated during
embryogenesis. Limb development relies on an exquisite coordination between growth and patterning but the underlying mechanisms
remain elusive. Previous studies showed that A-P and P-D limb bud growth and patterning relies on a positive feedback loop between
Sonic Hedgehog (Shh), the BMP antagonist Gremlin1 (Grem1), both expressed in mesenchymal cells, and Fibroblast growth factors
(Fgfs) produced in the Apical Ectodermal Ridge (AER). In addition, the collinear expression of HoxA and HoxD genes has a key role
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