“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.
Grape expectations (Fibroblast growth factor 9 signaling inhibits airway smooth muscle differentiation in mouse lung by Lan Yi, Eric T. Domyan, Mark Lewandoski, Xin Sun, Dev Dyn238:123–137) Mammalian lungs have a characteristic “bunch of grapes” morphology: the lungs are stems, its proximal end adjacent to bronchioles, and distal end closest to grape-shaped terminal sacs. Evidence suggests that localization of differentiated airway smooth muscle cells (SMCs) in the proximal, but not distal, lung is critical for organ function. Previous work showed that development of SMCs in the mesenchyme is regulated by FGF9 signaling from inner epithelial and outer mesothelial layers. With the low hanging fruit already picked, Yi and colleagues further tease apart the genetics of SMC development and differentiation. They show that knockout mice lacking Fgf9, or Fgf receptors 1 and 2 (Fgfr1;2) from lung mesenchyme both have ectopic airway SMCs in distal mesenchyme, suggesting FGF9 signals through FGFR1;2 to keep differentiated SMCs from the distal lung. Where do ectopic SMCs come from? Reduced Fgf10 expression in the distal mesenchyme, a marker for SMC precursors, suggests ectopic SMCs arise from precocious differentiation of progenitors. They further present genetic and pharmacological data demonstrating that SHH works in a pathway parallel to FGF9 to promote SMC differentiation. Tell it through the grapevine, their work suggests that FGF9 has dual functions: first to promote SMC precursor proliferation, and second to inhibit SMC differentiation from the distal lung.
Wringing out the truth (Dynamic organization and plasticity of sponge bodies by Mark J. Snee, Paul M. Macdonald, Dev Dyn238:918–930) Sponge bodies, cytoplasmic structures found in Drosophila egg chamber germline cells, are so named for their resemblance to a porous cleaning sponge. These ill-defined structures are thought to be akin to P-bodies, sites of mRNA storage, degradation, and posttranscriptional regulation. This idea is bolstered by Snee and Macdonald's discovery that sponge bodies bear four of six posttranscriptional regulators tested; of these regulators, Bru is enriched in nurse cells, and Orb in the oocyte. Close observation revealed that bodies exchange these components quickly, within 1 min. after entry into the oocyte from interconnected nurse cells. This finding is the first indication that sponge bodies are dynamic. The second indication is the bodies' dramatic morphological transformation under varying environmental conditions. Porous, “dispersed bodies” predominate when females are given food that favor egg-laying, while “reticulated bodies” predominate in virgins, and in females fed more standard fare. The third indication is that photobleaching experiments suggest Stau::GFP, and presumably associated oskar mRNA, moves transiently through sponge bodies as it makes its way to the posterior egg chamber as it matures. While some scrubbing sponges are made from cellulose, these data cleanly show that these sponge bodies are plastic.
Magnetic method (Ex vivo magnetofection: A novel strategy for the study of gene function in mouse organogenesis by Terje Svingen, Dagmar Wilhelm, Alexander N. Combes, Brett Hosking, Vincent R. Harley, Andrew H. Sinclair, Peter Koopman, Dev Dyn238:956–964) Most developmental biologists are familiar with the headaches of mouse transgenics: it is expensive, time-consuming, and technically challenging. Other gene transfer techniques, such as electroporation, can also be impractical or ineffective depending on experimental conditions. Koopman and colleagues have found that magnetofection is a viable alternative for their organ system, explanted genital ridges. With this technique, DNA is bound to magnetic particles, injected into the tissue of interest, and pulled into cells when placed next to a magnetic field. As proof-of-principle, genetic and morphological signs of sex reversal were triggered by magnetofection-induced ectopic expression of Sry in XX genital ridges, and by small interfering RNAs (siRNAs) against Sox9 in XY ridges. Using magnetofection, the authors misexpressed the Sertoli cell–specific Tmem184a in XX genital ridges, which is thought to promote the spermatogonia pathway in germ cells. Germ cells were prevented from entering meiosis—a prerequisite for female germ cell development—providing a mechanism of action for the gene. Although only 20% of genital ridges expressed introduced constructs, efficiency may improve with further experimental refinement. For those seeking a new way to alter gene expression in a developmental system, the pull of magnetofection may be hard to resist.