“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.
Finding a niche (Dev Dyn237:592–601) Some need to be in just the right environment, perhaps in the company of cocktails and good friends, before they can be themselves. Blentic and colleagues set out to find just what makes ectomesenchymal neural crest, precursors to bone, cartilage, connective tissue, and dentine, who they are. They find that upon entry to phyaryngeal arches, ectomesenchymal creast cease to transcribe Sox10, as assayed by reorter expression. Unlike other types of migratory crest, they also fail to express Foxd3, but upon entry to pharyngeal arches, crest cease to transcribe Sox10, as assayed by reporter expression. They also fail to express Foxd3, but initiate expression of the ectomesenchymal marker Dlx2. What is it about the arch environment that makes crest enter the ectomesenchymal lineage? Pharyngeal epithelia are a rich source of fibroblast growth factors (FGFs), prompting the authors to test the effect of blocking FGF signaling using pharmacological reagents in zebrafish, and ectopic expression of dominant negative FGF receptors in chick. In both cases, Sox10 and Foxd3 expression are activated, and Dlx2 diminished, suggesting entry into the ectomesenchymal fate is inhibited. Oddly, other sources of FGF encountered by newly emergent crest do not activate downstream FGF effectors nor do they launch Dlx2 expression. This means there must be additional components to a pharyngeal arch elixir that enable ectomesenchymal crest to feel at ease.
The versatile vertebrate (Dev Dyn237:861–882) Twenty years ago, who could have guessed that an aquarium favorite, the zebrafish, would wriggle its way into the research limelight? Originally hailed as a valuable resource for vertebrate forward genetics, its usefulness in reverse genetics is also rapidly coming to the fore. This review is a compendium of reverse genetics techniques that has something for everyone. The zebrafish novice will value thorough coverage of commonly used methods, including procedural overview, advantages and limitations, technical tips, and research applications. The established fish researcher will appreciate reports of obscure techniques, including those that should be easily transferable to the model system. Finally, the simply curious will gain new admiration for the aquatic wonder, and may be tempted to find ways to incorporate it into their work.
History comes alive (Dev Dyn237:953–961) Over 2,000 years ago Aristotle described the developing chicken embryo as seen by the naked eye, “After three days and a night…the heart…beats and moves as if it were alive”. If he thought this sight was impressive, he would be absolutely floored by the beautiful detail depicted in the movies presented here. In the chick, blood is pumped through an endocardial tube: a lumen surrounded by inner endothelium and outer myocardium walls between which lies an extracellular matrix, called cardiac jelly. The authors imaged the pumping heart in cross-section using optical coherence tomography (OCT), which makes possible real-time, high-resolution visualization of small structures in vivo. At diastole (dilation), the tube in cross-section resembles a thick “O”: the myocardium encircles a smaller endothelium circle. At systole (contraction), a smaller myocardial “o” is nearly bisected by a slit-shaped endothelium that closes off the lumen. The observed “eccentric” deformation of the endocardial tube challenges the prevailing 60-year-old model that documents “concentric” deformation, where both walls remain circular. The potential implications of this finding are described. They also note an uneven distribution of cardiac jelly, suggesting it could be the driving force behind the shape change. Within this study, is impressive documentation of the history of this field of research, making it easy to see why this contribution is important.