“Highlights” is a new feature that 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 will spotlight 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.
Absolutely FABAlous (Dev Dyn236:1790–1805) The next generation of staging tables has arrived. Studies using the basal chordate Ciona intestinalis promise to shed light on the evolutionary origins of vertebrates. However, lack of standardized embryonic staging has made interpretation of Ciona research difficult. Here, Hotta et al. present a Ciona staging table based on morphological characteristics with accompanying text that describes developmental milestones in detail. An interactive, Internet-based atlas, called Four-dimensional Ascidian Body Atlas (FABA) (http://chordate.bpni.bio.keio.ac.jp/faba/top.html), richly supplements the table. The atlas displays confocal laser scanning microscopy images of embryos stained with fluorescently labeled phalloidin, a molecule that labels cell membranes and other structures. The viewer can rotate three-dimensional images of a representative embryo from each developmental stage, and scroll through z-sections, allowing visualization of external and internal cellular arrangements. The planned integration of FABA with Ciona intestinalis Protein Database (CIPRO) will be a valuable enhancement.
Now Hear This (Dev Dyn236:1905–1917) Sometimes it is worthwhile to re-examine old data. Over a decade ago, inner ear defects in Fgfr3—/— mice were characterized by morphological analysis. Since then, molecular markers have been identified that distinguish cell types in the organ of Corti, the sensory epithelium of the inner ear. With these tools in hand, Puligilla and colleagues set out to better define the role of fibroblast growth factor receptor-3 (FGFR3) in this organ. They find that, in Fgfr3—/— cochlea, a reduction in inner pillar cell (IPC) number is accompanied by an increase in outer hair cell (OHC) and Deiters' cell numbers. However, cell death and overall proliferation are unaffected, suggesting that Fgfr3 commits precursor cells to the IPC fate. Bone morphogenetic protein-4 (BMP4), a known FGFR3 target, is up-regulated in Fgfr3—/— cochlea, and treatment of wild-type cochlear explant cultures with BMP4-soaked beads induces extra OHCs. These data support a model whereby Fgfr3 negatively regulates Bmp4, an interaction that mediates OHC fate choice. In agreement, treatment of Fgfr3—/— cochlear explants with Noggin, a BMP inhibitor, rescues the OHC phenotype. Additional Fgfr3—/— cochlea defects, including cochlear defects including aberrant innervation, and OHC and Dieter's cell differentiation are also described in careful detail.
Why Ascidians? (Dev Dyn236:1732–1747) Aside from having a good excuse to go to the beach, why use sea squirts as a model for developmental biology? This review is one of several in the Ciona Special Focus Issue that presents compelling answers to this question. The ascidian Ciona uses a small set of nonredundant genes to develop into a tadpole composed of approximately 2,500 cells. With a pared down chordate body plan, Ciona and other ascidians are accessible models useful for gaining a foothold on complex developmental events observed in other organisms. Kumano and Nishida's review highlights how these animals have furthered our understanding of cell fate specification. They begin by thoroughly covering the basics of ascidian embryology, including morphogenesis and cell lineage. Equipped with this knowledge, one is prepared for the next section, which compares and contrasts vertebrate and ascidian molecular mechanisms that govern cell fate specification. Many familiar players make appearances (β-catenin, Fgf, Notch, Fox, Gata, Ets), promising to keep the reader engaged.