“Highlights” calls attention to exciting advances in developmental biology that have recently been reported in Developmental Dynamics. Development is a broad field encompassing many important areas. To reflect this fact, the section spotlights significant discoveries that occur across the entire spectrum of developmental events and problems: from new experimental approaches, to novel interpretations of results, to noteworthy findings utilizing different developmental organisms.
An eye to the future (Embryonic chick corneal epithelium: A model system for exploring cell-matrix interactions, by Kathy K.H. Svoboda, Donald A. Fischman, Marion K. Gordon, Dev Dyn237:2667–2675) In 1944 Elizabeth D. Hay began her scientific career, and for more than five decades studied the role of the extracellular matrix in cell behavior and tissue development. In a special focus issue, Svoboda, Fischman, and Gordon review the advances made by Dr. Hay and her colleagues. Using electron microscopy, Dr Hay's group painstakingly detailed embryonic chick corneal epithelium responses to extracellular matrix—forming the basis for much future work using this system. Later studies revealed that an interaction between the epithelium and extracellular matrix molecules induce fibrillar collagen production by epithelial sheets, as well as local changes in the epithelial basal actin cytoskeleton. Such findings resulted in highly competitive and ongoing searches to identify molecules mediating these effects. Dr. Hay was a dedicated scientist whose discoveries helped carve out a unique area in the newly emerging field of cell biology. The cornea epithelium and its matrix are likely to be explored long into the future. Additional reviews and research articles in this memorial issue discuss the role of extracellular matrix in skeletal, palate, and corneal development as well as in disease.
Young and complex (Diverse roles of E-cadherin in the morphogenesis of the submandibular gland: Insights into the formation of acinar and ductal structures, by Janice L. Walker, A. Sue Menko, Sheede Khalil, Ivan Rebustini, Matthew P. Hoffman, Jordan A. Kreidberg, Maria A. Kukuruzinska, Dev Dyn237:3128–3141) Epithelial tissues such as salivary gland, lung, and kidney develop from a single bud with few distinguishing characteristics into a mature branched structure. The mature organs contain two important cell types: ductal cells surround the lumen of secondary branches, and acinar cells surround the terminal buds. By closely following development of cultured salivary glands from mice, Walker et al. found that young glands are more complex than previously thought. The authors show that, at the single bud stage, there is an outer layer of columnar cells and an inner layer of multiform cells. Surprisingly, even at this early stage, the outer layer expresses the neonatal acinar cell marker B1, which is now the earliest known marker for this cell fate. Moreover, outer cells have localized expression of the junctional protein E-cadherin, while the protein is diffuse in inner cells. Of interest, as gland development proceeds, E-cadherin becomes localized in inner ductal cell precursors coincident with lumen formation. While inhibition of E-cadherin using siRNA or antibody interference causes no obvious defects in outer acinar cell precursors where it is localized early, it causes apoptosis of inner ductal cell precursors leading to an expansion of the lumen. This study reveals that early salivary gland buds are indeed complex, and this feature is required for normal development.
Time to migrate? (Wnt11r is required for cranial neural crest migration, by Helen K. Matthews, Florence Broders-Bondon, Jean Paul Thiery, Roberto Mayor, Dev Dyn237:3404–3409) Neural crest (NC) is a transient embryonic tissue that gives rise to many diverse cell types, including neurons, glia, smooth muscle, and melanocytes. The NC migrates laterally from the position of its birth, adjacent to the neural tube, and eventually to multiple locations within the body. However, signals responsible for directional migration are not known. One candidate identified in Xenopus is noncononical wnt11, which is expressed in the right location, just lateral of the neural crest, and at the right time, just before migration. In addition, inhibition of wnt11 blocks NC migration, as would be expected for an attractive signal. However, Matthews et al. characterized a second Xenopuswnt11-related molecule, and their study makes this hypothesis less appealing. One reason is that, although wnt11r has a phenotype similar to wnt11 based on morpholino knockdowns, it is expressed in the neural tube, on the opposite side of the neural crest. Thus, the NC is surrounded by two wnt11-like morphogens, both of which appear to have an active role in migration. While it is still possible that wnt11 controls the direction of NC migration, further models should now be considered—for instance, perhaps both molecules are necessary to ensure that all neural crest cells will receive the right level of non-canonical Wnt ligand at the right time.