Abstracts - Society for Developmental Biology

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disrupts ovary development even more severely than vasa-null. We propose that this effect is associated with a decreased
specificity of the protein, essentially blocking some other proteins from their mRNA targets. To confirm this, we will use
deep sequencing analysis to compare RNAs bound to different Vasa truncates used in this study.
Program/Abstract # 405
Understanding the craniofacial defects produced by inhibition of folic acid metabolism
Ahlgren, Sara C., Northwestern Univ Feinberg Sch of Med, Chicago, United States; Erhard, Stephanie (Children's
Memorial Research Center, Chicago, U.S.A.)
It has been demonstrated that women who take folic acid prior to and during pregnancy reduce their chance of a number of
structural birth defects, primarily neural tube defects but also facial defects including. The mechanisms by which folic acid
reduces birth defects, and conversely, the mechanisms by which a reduction of folic acid and folate one-carbon metabolism
contribute to birth defects, are not fully understood. The developmental consequences of reduced folate one-carbon
metabolism have been studied for the neural tube and heart but less well understood for craniofacial regions. The zebrafish
embryo can be studied in large numbers and have been demonstrated to have similar folate related one-carbon pathways as
mammals and can provide insight into the mechanisms by which folate deficiency can impact human birth defects. We
have determined that, by using the antifolate drug methotrexate (MTX) during early gastrulation through early neural crest
migration stages, there is a dose-dependent effect on the size but not the patterning of cartilage elements when analyzed
later in the developing larva. We seek to interrogate the neural crest to determine what developmental process is primarily
disrupted in this model system.
Program/Abstract # 406
Hypertrophic chondrocytes contribute directly to the osteoblast and osteocyte lineage in endochondral bones in
vivo
Cheah, Kathryn S.; Yang, Liu; Tang, Tiffany; Tsang, Kwok Yeung; Dung, Nelson WF; Chan, Danny, University of Hong
Kong, Hong Kong
It is widely accepted that in vertebrates, bone formation occurs via one of two processes - membranous bone formation in
which osteoblasts directly differentiate from mesenchymal cells or via endochondral ossification (EO), a multistep process
wherein chondrocytes differentiate from mesenchymal condensations, to form a cartilaginous template, proliferate, exit the
cell cycle to undergo hypertrophy and terminal differentiation. Vascular invasion occurs, and hypertrophic chondrocytes
(HCs) are thought to undergo apoptosis, while bone is laid down by osteoblasts from the periosteum and bone collar
surrounding the hypertrophic zone, replacing cartilage. However whether in vivo, all HCs undergo apoptosis in EO or can
become osteoblasts has been a subject of considerable controversy. To address this controversy we have followed the fate
of HCs using the Cre-loxP system in mice. We used homologous recombination to generate two cre lines, Col10a1-cre and
Col10a1-creER TM , which express Cre recombinase under the control of HC-specific Col10a1 gene. We genetically tagged
HCs by crossing Col10a1-cre mice to Cre-reporter mice (Rosa-26R-LacZ or Rosa-26R-YFP) and performed cell-lineage
analyses to track the fate of HCs in fetal and postnatal stages. These experiments in combination with pulse-chase
experiments using tamoxifen induction of Cre activity in Col10a1-creER TM ; Rosa-26R-LacZ mice, show that in vivo, HCs
contribute directly to the osteoblast and osteocyte lineage of ALL endochondral bones. These osteoblasts of HC origin
(HCObs) contribute to about a third of bone cells in long bones. In a bone-injury model we further show that HCObs
contribute to new bone formation in the healing process. These discoveries impact on our current understanding of the
origin of bone cells and have translational implications for regenerative medicine.
Program/Abstract # 407
Development of the autopod, but not of proximal skeletal elements, is impaired by misexpression of the BMPbinding
molecule Chordin-like 1 in the chick limb
Allen, Justin, Boston Children's Hospital, Brookline, United States; McGlinn, Edwina; Tabin, Cliff; Warman, Matthew
(Boston, United States)
The BMP-binding molecule Chordin-like 1 (Chrdl1) is expressed in mesenchymal lineages, including progenitors of
skeletal tissues, but its role in skeletal development has not been examined in detail. We report that Chrdl1 is strongly
expressed in limb buds and in somites of chick embryos. To further investigate the function of Chrdl1 in skeletal
development, we utilized a gain-of-function approach using the RCAS viral expression system to misexpress Chrdl1 in
developing limbs. Overexpression of Chrdl1 in the chick limb resulted in a severe oligodactyly phenotype, with a loss of
anterior digits and of distal phalanges, although skeletal elements proximal to the autopod developed normally. Whole
mount in situ hybridization analysis of genes important for limb development revealed that Shh and FGF signaling were
upregulated, and FGF signaling from the apical ectodermal ridge persisted later in development in Chrdl1-overexpressing