Msx1 and Dlx5 function synergistically to regulate frontal bone development

The Msx and Dlx families of homeobox proteins are important regulators for embryogenesis. Loss of Msx1 in mice results in multiple developmental defects including craniofacial malformations. Although Dlx5 is widely expressed during embryonic development, targeted null mutation of Dlx5 mainly affects the development of craniofacial bones. Msx1 and Dlx5 show overlapping expression patterns during frontal bone development. To investigate the functional significance of Msx1/Dlx5 interaction in regulating frontal bone development, we generated Msx1 and Dlx5 double null mutant mice. In Msx1^?/?;Dlx5^?/? mice, the frontal bones defect was more severe than that of either Msx1^?/? or Dlx5^?/? mice. This aggravated frontal bone defect suggests that Msx1 and Dlx5 function synergistically to regulate osteogenesis. This synergistic effect of Msx1 and Dlx5 on the frontal bone represents a tissue specific mode of interaction of the Msx and Dlx genes. Furthermore, Dlx5 requires Msx1 for its expression in the context of frontal bone development. Our study shows that Msx1/Dlx5 interaction is crucial for osteogenic induction during frontal bone development. genesis 48:645–655, 2010. © 2010 Wiley‐Liss, Inc.     

Spatio‐temporal dynamics of gene expression of the Edn1‐Dlx5/6 pathway during development of the lower jaw

The morphogenesis of the vertebrate skull results from highly dynamic integrated processes involving the exchange of signals between the ectoderm, the endoderm, and cephalic neural crest cells (CNCCs). Before migration CNCCs are not committed to form any specific skull element, molecular signals exchanged in restricted regions of tissue interaction are crucial in providing positional identity to the CNCCs mesenchyme and activate the specific morphogenetic process of different skeletal components of the head. In particular, the endothelin‐1 (Edn1)‐dependent activation of Dlx5 and Dlx6 in CNCCs that colonize the first pharyngeal arch (PA1) is necessary and sufficient to specify maxillo‐mandibular identity. Here, to better analyze the spatio‐temporal dynamics of this process, we associate quantitative gene expression analysis with detailed examination of skeletal phenotypes resulting from combined allelic reduction of Edn1, Dlx5, and Dlx6. We show that Edn1‐dependent and ‐independent regulatory pathways act at different developmental times in distinct regions of PA1. The Edn1→Dlx5/6→Hand2 pathway is already active at E9.5 during early stages of CNCCs colonization. At later stages (E10.5) the scenario is more complex: we propose a model in which PA1 is subdivided into four adjacent territories in which distinct regulations are taking place. This new developmental model may provide a conceptual framework to interpret the craniofacial malformations present in several mouse mutants and in human first arch syndromes. More in general, our findings emphasize the importance of quantitative gene expression in the fine control of morphogenetic events. genesis 48:362–373, 2010. © 2010 Wiley‐Liss, Inc.     

The avian embryo as a model to study the development of the neural crest: a long and still ongoing story

The aim of this review is to evoke briefly the progress that has been made in our knowledge about the contribution of the neural crest to the vertebrate body since it was discovered by Wilhelm His in 1868. Although first studied essentially in amphibian embryos, a large amount of what is known on this very special structure was gained by experimental work carried out on the avian embryo. The making of chimeras between quail and chick has permitted not only to analyse the normal course of neural crest cell migration and differentiation but also to reveal some of the cellular interactions that regulate these events. Looking to the future, we can foresee that the novel methods, which now allow to manipulate gene activities in definite groups of cells and at elected times in the developing embryo, will make the avian model even more instrumental than ever to approach the developmental problems raised by neural crest cell differentiation.     

Intrinsic differences among spatially distinct neural crest stem cells in terms of migratory properties, fate determination, and ability to colonize the enteric nervous system

We have systematically examined the developmental potential of neural crest stem cells from the enteric nervous system (gut NCSCs) in vivo to evaluate their potential use in cellular therapy for Hirschsprung disease and to assess differences in the properties of postmigratory NCSCs from different regions of the developing peripheral nervous system (PNS). When transplanted into developing chicks, flow-cytometrically purified gut NCSCs and sciatic nerve NCSCs exhibited intrinsic differences in migratory potential and neurogenic capacity throughout the developing PNS. Most strikingly, gut NCSCs migrated into the developing gut and formed enteric neurons, while sciatic nerve NCSCs failed to migrate into the gut or to make enteric neurons, even when transplanted into the gut wall. Enteric potential is therefore not a general property of NCSCs. Gut NCSCs also formed cholinergic neurons in parasympathetic ganglia, but rarely formed noradrenergic sympathetic neurons or sensory neurons. Supporting the potential for autologous transplants in Hirschsprung disease, we observed that Endothelin receptor B (Ednrb)-deficient gut NCSCs engrafted and formed neurons as efficiently in the Ednrb-deficient hindgut as did wild-type NCSCs. These results demonstrate intrinsic differences in the migratory properties and developmental potentials of regionally distinct NCSCs, indicating that it is critical to match the physiological properties of neural stem cells to the goals of proposed cell therapies.