Dandy Walker Malformation, the most common human cerebellarbirth defect, is caused by heterozygous deletion of Zic1 and Zic4. InZic1/4 single and double null mice, cerebellar phenotypes range frommildly reduced size with normal folial patterning, to severely smalland mispatterned cerebella. The developmental basis of thesephenotypes remains unknown and little is understood regarding themolecular pathways regulated by the Zic genes. We observe reducedgranule cell (GC) proliferation in Zic1−/−;Zic4−/− mice at post-natalday one. Shh drives GC proliferation during early neonatal develop-ment, suggesting the hypothesis that Zic1 and Zic4 may act in the Shhpathway. At embryonic day 17.5, Zic1−/−;Zic4−/− cerebella demon-strate 2–4 fold reduction in expression of several Shh target genes,including Gli1 and Ptch1, supporting a role for Zic1 and Zic4 in the Shhpathway. Several members of the Eph/Ephrin family also have reducedexpression, although these genes have not been implicated in Shhdependent proliferation. This may indicate that adult cerebellarfoliation defects have a Shh independent component. In situ hybrid-ization at e17.5 shows that, in Zic mutants, EphA4 and EphA7 ex-pression patterns are altered in the anterior medial domain of thedeveloping cerebellum. This altered expression presages abnormalpositioning of anterior folia, suggesting that Zic function is critical fordetermining the placement of the initial cardinal folia of the anteriorcerebellum. Further experiments are underway to determine if sizeand foliation defects are related.

doi:10.1016/j.ydbio.2008.05.506

Program/Abstract # 430Genetic and functional interaction between transcription factorsMEF2C and Dlx5/6 is required for craniofacial developmentPooja Agarwal, Michael P. Verzi, Brian L. BlackCVRI, University of California, San Francisco, CA, USA

Congenital craniofacial anomalies are among the most commoncause of birth defects in infants, signifying the importance ofunderstanding the molecular basis of craniofacial development. Ourstudy focuses on the genetic and functional interaction between theMADS domain transcription factor MEF2C and two Dlx home-odomain transcription factors, Dlx5 and Dlx6. Neural crest-specificinactivation of Mef2c causes craniofacial lethality in mice. MEF2C isrequired for Dlx5 and Dlx6 expression in the craniofacial mesench-yme during development, and can transcriptionally synergize withDlx5. We hypothesize that MEF2C and Dlx5 form a transcriptionalcomplex essential for craniofacial development. Our current studiesfocus on elucidating the biochemical basis of the Dlx5–MEF2Cinteraction and identifying genes that are exquisitely sensitive tothe dosage of these two factors. We show a genetic interactionbetween the Mef2c and Dlx5/6 loci where heterozygosity at eitherlocus (Dlx5/6+/− or Mef2c+/−) results in viable mice with no obviousphenotype but heterozygosity at both loci (Dlx5/6+/−;Mef2c+/−) resultsin perinatal lethality. Dlx5/6+/−;Mef2c+/− mice have defective man-dibular outgrowth resulting in micrognathia and a posterior cleft ofthe palate. This mandibular defect is highly reminiscent of thePierre Robin sequence (PRS) in humans and Dlx5/6+/−;Mef2c+/− micecould serve as a mouse model for PRS. Understanding the inter-action between Dlx5/6 and MEF2C will contribute to our under-standing of craniofacial development and how interactions bet-ween MADS box and homeodomain transcription factors regulateorganogenesis.

doi:10.1016/j.ydbio.2008.05.507

Program/Abstract # 431Functional equivalence between Osr1 and Osr2 in mousedevelopmentYang Gao, Yu Lan, Catherine E. Ovitt, Rulang JiangDepartment of Biomedical Genetics, University of Rochester, Rochester,NY, USACenter for Oral Biology, University of Rochester, Rochester, NY, USA

The Odd-skipped gene was originally identified in Drosophila asan essential regulator of embryonic development and patterning.Two mouse homologs, odd-skipped related 1 (Osr1) and odd-skippedrelated 2 (Osr2) have been identified. Interestingly, whereas theDrosophila odd-skipped gene encodes a protein with four C2H2-typezinc finger motifs, mouse Osr1 encodes a protein with three zincfingers and Osr2 encodes both a three-finger and a five-finger proteindue to alternative splicing of the pre-mRNA. Targeted disruption ofeither gene caused distinct developmental defects that largelycorrelate with their distinct expression patterns. To investigatewhether the two genes have evolved distinct functions at themolecular level and whether the two Osr2 isoforms functiondifferently during mouse development, we replaced the endogenousOsr2 coding region with either the Osr1 cDNA encoding for the three-finger Osr1 protein or the Osr2-5F cDNA encoding the five-fingerOsr2 protein isoform. Expression of either Osr1 or Osr2-5F from theOsr2 locus similarly rescued cleft palate phenotype of the Osr2 nullmutants. These data indicate that the distinct functions of Osr1 andOsr2 during mouse embryonic development result from differentialexpression rather than distinct molecular function and that the twoisoforms of Osr2 protein likely function redundantly during palatedevelopment.

doi:10.1016/j.ydbio.2008.05.508

Program/Abstract # 432The role of Dlx3 in hair developmentJoonsung Hwang a, Taraneh Mehrani a, Sarah E. Millar b,Maria I. Morasso a

a Developmental Skin Biology Unit, NIAMS, NIH, Bethesda,MD 20892, USAb Department of Dermatology and Cell and Developmental Biology,University of Pennsylvania School of Medicine, Philadelphia,PA 19104, USA

The Dlx3 homeodomain transcription factor is crucial for develop-mental processes including tissue differentiation and organ formation.Tricho-Dento-Osseous Syndrome (TDO) is an ectodermal dysplasialinked to a 4 bp deletion immediately downstream of the DNA-bindinghomeodomain in the Dlx3 gene and that is characterized byabnormalities in hair, teeth, and intramembranous and ectochondralbones. To examine Dlx3 gene expression throughout development, wegenerated a knockin mouse line carrying the reporter gene beta-galactosidase (lacZ) under the control of the endogenous Dlx3promoter. Dlx3 expression is detected in tissues and organs derivedfrom epithelial-mesenchymal interactions such as hair follicles, teethand limbs, and in craniofacial bones and interfollicular epidermis. Wehave characterized Dlx3 expression through hair differentiation andgrowth cycle. Dlx3 expression was initially detected in the matrix ofhair follicles directly adjacent to dermal papilla, and then graduallyextended to inner root sheath (IRS), cortex, medulla, and cuticle of thedifferentiating hair. The role of Dlx3 in hair development is beinginvestigated intensively using a Cre-mediated knockoutmousemodel.The most striking defect in those mice was alopecia due to a failurein hair follicle differentiation. Taken together with pathological

595ABSTRACTS / Developmental Biology 319 (2008) 587–598