What Do Animal Models Teach Us About Congenital Craniofacial Defects?

The formation of the head and face is a complex process which involves many different signaling cues regulating the migration, differentiation, and proliferation of the neural crest. This highly complex process is very error-prone, resulting in craniofacial defects in nearly 10,000 births in the United States annually. Due to the highly conserved mechanisms of craniofacial development, animal models are widely used to understand the pathogenesis of various human diseases and assist in the diagnosis and generation of preventative therapies and treatments. Here, we provide a brief background of craniofacial development and discuss several rare diseases affecting craniofacial bone development. We focus on rare congenital diseases of the cranial bone, facial jaw bones, and two classes of diseases, ciliopathies and RASopathies. Studying the animal models of these rare diseases sheds light not only on the etiology and pathology of each disease, but also provides meaningful insights towards the mechanisms which regulate normal development of the head and face.

The 14-3-3 Protein Homolog ArtA Regulates Development and Secondary Metabolism in the Opportunistic Plant Pathogen Aspergillus flavus.

The opportunistic plant-pathogenic fungus Aspergillus flavus produces carcinogenic mycotoxins termed aflatoxins (AF). Aflatoxin contamination of agriculturally important crops, such as maize, peanut, sorghum, and tree nuts, is responsible for serious adverse health and economic impacts worldwide. In order to identify possible genetic targets to reduce AF contamination, we have characterized the artA gene, encoding a putative 14-3-3 homolog in A. flavus The artA deletion mutant presents a slight decrease in vegetative growth and alterations in morphological development and secondary metabolism. Specifically, artA affects conidiation, and this effect is influenced by the type of substrate and culture condition. In addition, normal levels of artA are required for sclerotial development. Importantly, artA negatively regulates AF production as well as the concomitant expression of genes in the AF gene cluster. An increase in AF is also observed in seeds infected with the A. flavus strain lacking artA Furthermore, the expression of other secondary metabolite genes is also artA dependent, including genes in the cyclopiazonic acid (CPA) and ustiloxin gene clusters, in this agriculturally important fungus.IMPORTANCE In the current study, artA, which encodes a 14-3-3 homolog, was characterized in the agriculturally and medically important fungus Aspergillus flavus, specifically, its possible role governing sporulation, formation of resistant structures, and secondary metabolism. The highly conserved artA is necessary for normal fungal morphogenesis in an environment-dependent manner, affecting the balance between production of conidiophores and the formation of resistant structures that are necessary for the dissemination and survival of this opportunistic pathogen. This study reports a 14-3-3 protein affecting secondary metabolism in filamentous fungi. Importantly, artA regulates the biosynthesis of the potent carcinogenic compound aflatoxin B1 (AFB1) as well as the production of other secondary metabolites.

Injection of human neuroblastoma cells into neural crest streams in live zebrafish embryos.

Cancer cell behavior is highly microenvironment dependent, but we have a limited understanding of malignant cell-microenvironment interactions in vivo. Here, we describe a protocol for xenotransplanting human neuroblastoma (NB) cells into streams of migrating neural crest stem cells in zebrafish embryos, followed by confocal time-lapse imaging and cell tracking. This high-resolution model system facilitates the quantitative spatiotemporal analysis of cancer cell-cell and cell-environment interactions. For complete details on the use and execution of this protocol, please refer to Treffy et al. (2021).

Wnt-Dependent Activation of ERK Mediates Repression of Chondrocyte Fate during Calvarial Development.

Wnt signaling regulates cell fate decisions in diverse contexts during development, and loss of Wnt signaling in the cranial mesenchyme results in a robust and binary cell fate switch from cranial bone to ectopic cartilage. The Extracellular signal-regulated protein kinase 1 and 2 (ERK1/2) and Wnt signaling pathways are activated during calvarial osteoblast cell fate selection. Here, we test the hypothesis that ERK signaling is a mediator of Wnt-dependent cell fate decisions in the cranial mesenchyme. First, we show that loss of Erk1/2 in the cranial mesenchyme results in a diminished domain of osteoblast marker expression and increased expression of cartilage fate markers and ectopic cartilage formation in the frontal bone primordia. Second, we show that mesenchyme Wnt/ß-catenin signaling and Wntless are required for ERK activation in calvarial osteoblasts. Third, we demonstrate that Wnt and ERK signaling pathways function together to repress SOX9 expression in mouse cranial mesenchyme. Our results demonstrate an interaction between the Wnt and ERK signaling pathways in regulating lineage selection in a subset of calvarial cells and provide new insights into Wnt-dependent cell fate decisions.