“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.

Bending the rules (Neuro-Mesodermal Patterns in Artificially Deformed Embryonic Explants: A Role for Mechano-Geometry in Tissue Differentiation by E.S. Kornikova, T.G. Troshina, S.V. Kremnyov, and L.V. Beloussov, Dev Dyn239:885–896) In Embryology 101, students learn that opposing gradients of secreted proteins pattern the gastrula embryo. Here, Kornikova et al. present evidence that an entirely different category of patterning mechanisms have been overlooked—mechano-geometry, or cell shape changes caused by external forces. Xenopus midgastrula suprablastoporal (SBA) ectoderm sandwiches—double cell layers from the marginal zone above the blastopore—were artificially bent by inserting and culturing them in curved beds dug into agarose. After 3 hr, the explants were removed, yet they continued a self-imposed extension of the convex surface and contraction of the concave surface. After at least 20 hr in culture, the anterior–posterior polarity of artificially bent explants varied considerably from controls, despite evidence that there was little cell mixing between the opposite sides of sandwiches. Histology and gene expression analysis showed that, regardless of being parallel or perpendicular to the anterior–posterior polarity bending, neural rudiments in bent explants localized to concave cells while the mesodermal rudiment surrounded it in a horseshoe-like manner. By contrast, in unbent explants, neural rudiments resided at the anterior tip and the mesoderm posterior. The authors cite evidence suggesting that artificial bending mimics native forces exerted by surrounding cells in vivo and suggest that mechano-dependence of gene expression is a force to be reckoned with.

Folate deficiency at fault (High-Affinity Folate Receptor in Cardiac Neural Crest Migration: A Gene Knockdown Model Using siRNA by Thomas H. Rosenquist, Tammy Chaudoin, Richard H. Finnell, and Gregory D. Bennett. Dev Dyn239:1136–1144) Mothers-to-be are taught that folate supplements will reduce the risk of fetal neural tube defects. The study highlighted here addresses mechanisms behind the lesser-known observation that folate supplementation also reduces the risk of outflow tract (conotruncal) heart defects. The folate transporter Folr1 is highly expressed in the developing neural tube (NT) and the cardiac neural crest (CNC), which give rise to specific regions of the heart. To investigate the role of folate in heart development, the authors used electroporation to introduce a Folr1-suppressing short interfering RNA (siRNA) into premigratory chick CNC in vivo. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis demonstrated that Folr1 expression was reduced 1-day after electroporation. Affected embryos had malformed hearts consistent with a lack of CNC that failed to migrate through the pharyngeal arches and to the developing heart. In addition, mitosis was reduced in the electroporated cells, suggesting the defects could arise from a variety of primary causes. Possibilities include a reduced number of NC precursors, an impaired ability of cells to become CNC precursors, and/or aberrant NT-based NC migration cues—any of which are compelling reasons to take prenatal vitamins.

Mapping muscle (Temporal and Spatial Patterning of Axial Myotome Fibers in Xenopus laevis by Vanja Krneta-Stankic, Armbien Sabillo, and Carmen R. Domingo, Dev Dyn239:1162–1177) Where you come from can tell something about who you are. With this in mind, Krneta-Stankic et al., fate mapped the Xenopus gastrula to determine the origin of muscle cells within somites, paired blocks of tissue that develop adjacent to the notochord. They find that upper lateral lip (ULL) and lower lip (LL) circumblastoporal cells mostly contribute to myofibers in distinct domains within somites along much of the axis, such that a single somite can originate from both cell types. Heterotopic transplantations show the cells are interchangeable, suggesting myofiber position is an outcome of gastrulation movements. What s more, when gastrula cells and presomitic mesoderm (PSM) cells are each transplanted to anterior somites, the PSM cells form myofibers, but gastrula cells do not. These results demonstrate that, between the gastrula and PSM, there is a maturation process that enhances their ability to become myofibers. As for many, somite muscle is a product of their ancestors' travels and hard work