ABSTRACT
The Hedgehog signaling pathway is critical for a significant number of developmental patterning events. In this study, we focus on the defects in pharyngeal arch and cardiovascular patterning present in Sonic hedgehog (Shh) null mouse embryos. Our data indicate that, in the absence of Shh, there is general failure of the pharyngeal arch development leading to cardiac and craniofacial defects. The cardiac phenotype results from arch artery and outflow tract patterning defects, as well as abnormal development of migratory neural crest cells (NCCs). The constellation of cardiovascular defects resembles a severe form of the human birth defect syndrome tetralogy of Fallot with complete pulmonary artery atresia. Previous studies have demonstrated a role for Shh in NCC survival and proliferation at later stages of development. Our data suggest that SHH signaling does not act directly on NCCs as a survival factor, but rather acts to restrict the domains that NCCs can populate during early stages (e8.5-10.5) of cardiovascular and craniofacial development.
Subject(s)
Arteries/embryology , Body Patterning , Neural Crest/embryology , Trans-Activators/genetics , Animals , Branchial Region/embryology , Cell Death , Cell Proliferation , Endoderm/physiology , Female , Heart/embryology , Hedgehog Proteins , Intracellular Signaling Peptides and Proteins , Male , Membrane Proteins/biosynthesis , Mice , Mice, Knockout , Neural Crest/cytology , Neural Crest/metabolism , Patched Receptors , Receptors, Cell Surface , Signal TransductionABSTRACT
Development of the vertebrate limb bud depends on reciprocal interactions between the zone of polarizing activity (ZPA) and the apical ectodermal ridge (AER). Sonic hedgehog (SHH) and fibroblast growth factors (FGFs) are key signalling molecules produced in the ZPA and AER, respectively. Experiments in chicks suggested that SHH expression in the ZPA is maintained by FGF4 expression in the AER, and vice versa, providing a molecular mechanism for coordinating the activities of these two signalling centres. This SHH/FGF4 feedback loop model is supported by genetic evidence showing that Fgf4 expression is not maintained in Shh-/- mouse limbs. We report here that Shh expression is maintained and limb formation is normal when Fgf4 is inactivated in mouse limbs, thus contradicting the model. We also found that maintenance of Fgf9 and Fgf17 expression is dependent on Shh, whereas Fgf8 expression is not. We discuss a model in which no individual Fgf expressed in the AER (AER-Fgf) is solely necessary to maintain Shh expression, but, instead, the combined activities of two or more AER-Fgfs function in a positive feedback loop with Shh to control limb development.
Subject(s)
Fibroblast Growth Factors/genetics , Fibroblast Growth Factors/metabolism , Gene Expression Regulation, Developmental , Limb Buds/embryology , Proto-Oncogene Proteins/genetics , Proto-Oncogene Proteins/metabolism , Receptors, Cell Surface , Signal Transduction/genetics , Trans-Activators , Viral Proteins , Animals , DNA-Binding Proteins/genetics , Ectoderm/metabolism , Ectoderm/physiology , Egg Proteins/genetics , Feedback/physiology , Fibroblast Growth Factor 4 , Genes, Lethal , Hedgehog Proteins , Homeodomain Proteins , Integrases/genetics , Membrane Glycoproteins/genetics , Mice , Mice, Inbred C57BL , Mice, Knockout , Mice, Transgenic , Proteins/genetics , Zona Pellucida/physiology , Zona Pellucida GlycoproteinsABSTRACT
A molecular pathway leading to left-right asymmetry in the chick embryo has been described, in which FGF8 is a right determinant and Sonic Hedgehog a left determinant. Here evidence is presented that the Fgf8 and Sonic Hedgehog genes are required for left-right axis determination in the mouse embryo, but that they have different functions from those previously reported in the chick. In the mouse FGF8 is a left determinant and Sonic Hedgehog is required to prevent left determinants from being expressed on the right.
Subject(s)
Body Patterning , Chick Embryo/growth & development , Embryonic Induction , Embryonic and Fetal Development , Fibroblast Growth Factors/physiology , Nuclear Proteins , Proteins/physiology , Trans-Activators , Animals , Chick Embryo/metabolism , Embryo, Mammalian/metabolism , Fibroblast Growth Factor 8 , Fibroblast Growth Factors/genetics , Gene Expression Regulation, Developmental , Heart/embryology , Heart Defects, Congenital/embryology , Hedgehog Proteins , Homeodomain Proteins/genetics , Homeodomain Proteins/physiology , Left-Right Determination Factors , Lung/abnormalities , Lung/embryology , Mesoderm/metabolism , Mice , Mutation , Nodal Protein , Paired Box Transcription Factors , Proteins/genetics , Recombinant Proteins/metabolism , Transcription Factors/genetics , Transcription Factors/physiology , Transforming Growth Factor beta/genetics , Transforming Growth Factor beta/physiology , Homeobox Protein PITX2ABSTRACT
Fgf8 and Fgf4 encode FGF family members that are coexpressed in the primitive streak of the gastrulating mouse embryo. We have analyzed the phenotype of Fgf8(-/-) embryos and discovered that they fail to express Fgf4 in the streak. In the absence of both FGF8 and FGF4, epiblast cells move into the streak and undergo an epithelial-to-mesenchymal transition, but most cells then fail to move away from the streak. As a consequence, no embryonic mesoderm- or endoderm-derived tissues develop, although extraembryonic tissues form. Patterning of the prospective neuroectoderm is greatly perturbed in the mutant embryos. Anterior neuroectoderm markers are widely expressed, at least in part because the anterior visceral endoderm, which provides signals that regulate their expression, is not displaced proximally in the absence of definitive endoderm. Posterior neuroectoderm markers are not expressed, presumably because there is neither mesendoderm underlying the prospective neuroectoderm nor a morphologically normal node to provide the inductive signals necessary for their expression. This study identifies Fgf8 as a gene essential for gastrulation and shows that signaling via FGF8 and/or FGF4 is required for cell migration away from the primitive streak.
Subject(s)
Cell Movement/genetics , Fibroblast Growth Factors/genetics , Gastrula/cytology , Animals , Base Sequence , DNA Primers , Embryonic and Fetal Development/genetics , Gene Expression Regulation, Developmental , Homozygote , Mice , Signal TransductionABSTRACT
We describe a strategy for generating an allelic series of mutations at a given locus that requires the production of only one targetted mouse line. The 'allelogenic' mouse line we produced carries a hypomorphic allele of Fgf8, which can be converted to a null allele by mating to cre transgenic animals. The hypomorphic allele can also be reverted to wild-type by mating the allelogenic mice to flp transgenic animals, thereby generating a mouse line suitable for Cre-induced tissue-specific knockout experiments. Analysis of embryos carrying different combinations of these alleles revealed requirements for Fgf8 gene function during gastrulation, as well as cardiac, craniofacial, forebrain, midbrain and cerebellar development.
Subject(s)
Congenital Abnormalities/genetics , DNA Nucleotidyltransferases/metabolism , Fibroblast Growth Factors , Growth Substances/genetics , Integrases/metabolism , Recombination, Genetic , Viral Proteins , Actins/genetics , Alleles , Animals , Congenital Abnormalities/embryology , Crosses, Genetic , Embryonic and Fetal Development , Fibroblast Growth Factor 8 , Gene Library , Growth Substances/biosynthesis , Humans , Mice , Mice, Transgenic , Polymerase Chain Reaction , Promoter Regions, GeneticSubject(s)
Embryonic Induction/physiology , Embryonic and Fetal Development/physiology , Fibroblast Growth Factors/biosynthesis , Gene Expression Regulation, Developmental , Vertebrates/embryology , Animals , Body Patterning , Brain/embryology , Fibroblast Growth Factor 8 , Mice , Models, Biological , Receptors, Fibroblast Growth Factor/biosynthesis , Receptors, Fibroblast Growth Factor/physiologyABSTRACT
Pigmented villonodular synovitis (PVNS) rarely occurs in the temporomandibular joint. The bony changes are easily assessed by tomography. Pluridirectional tomography cannot, however, evaluate the soft tissue component of the lesion especially that medial to the mandibular condyle. This area is accessible to CT scan evaluation. A case is presented in which the medial extent of the lesion was determined by CT scan. The radiologic findings of PVNS of the temporomandibular joint are discussed.