“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.
Shapely models (Dev Dyn 2006;235:2907–2919) In classic experiments, Spemann and Mangold transplanted dorsal “organizer” cells from one newt to another, creating the unforgettable two-headed embryo. This and later works led to the hypothesis that the Spemann organizer specifies the primary body axes. In this review, Meinhardt eschews convention and proposes that the Spemann organizer plays a secondary role in axis formation. His model states that the head anterior/posterior (AP) axis is specified by the blastopore, and the trunk's by oscillating expression of sequentially posteriorizing genes. The role of the Spemann organizer is to trigger formation of head and trunk midline organizers (prechordal plate and notochord), which specify the dorsal/ventral (DV) axis. Unlike other models, Meinhardt's predicts the correct AP and DV orientation of an induced second axis. This provocative model will surely shape the interpretation of results from both new and old experiments in the field.
Creating boundaries (Dev Dyn 2006;235:3051–3058) Like a border fence between countries, cells with distinct fates need boundaries to keep one population from invading the other. Major and Irvine show for the first time that, in the Drosophila wing disc, Myosin II is a necessary boundary component downstream of Notch signaling. Of interest, Myosin II is required for DV, but not AP compartmentalization, showing that not all boundaries are alike. Building on their previous work, the authors propose that Myosin II creates a contractile force along an F-actin cable, making a physical barrier separating dorsal and ventral wing disc cells.
Navigating theXenopusembryo (Dev Dyn 2006;235:3059–3062). A frustration shared among Xenopus biologists is their inability to visualize individual cells in the depths of the murky, yolk-filled embryo. Finally, Jacobs' group has found a way to navigate through uncharted territory. They report that two dimensional microscopic magnetic resonance imaging (mMRI) successfully images the orientation, timing, and lineage of cell divisions. Ironically, the often-despised yolk benefits this technique. Its uneven distribution in a cell provides imaging contrast, enabling identification of animal and vegetal poles, blastocele, cell nuclei, and membranes without contrast enhancing labeling. This tool will make the already proven Xenopus model system even more powerful.