“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.
Tankyrase is tonic (Tankyrase Is Necessary for Canonical Wnt Signaling During Kidney Development by Courtney M. Karner, Calli E. Merkel, Michael Dodge, Zhiqiang Ma, Jianming Lu, Chuo Chen, Lawrence Lum, and Thomas J. Carroll, Dev Dyn239:2014–2023) Tankyrase (Tnk) 1 and 2 are another of a seemingly ever-growing list of canonical Wnt pathway components. They are poly (ADP ribose) polymerases (PARPs) that destabilize Axin 1 and 2, components of the Wnt pathway destruction complex. Molecular biologists are drunk with excitement about their discovery because they are also targets of the small molecule antagonist IWR1, an inhibitor of canonical Wnt signaling. Here, Karner and colleagues test whether Tnks are general Wnt pathway components that operate during mouse development. Supporting this hypothesis, expression of Tnks1 and 2 mirrors sites of Wnt pathway activation, and application of IWR1 to organ cultures inhibits the β-catenin–dependent processes of lung and kidney branching morphogenesis. The authors also show that, when applied to kidney organ cultures, IWR1 specifically targets the Wnt pathway. IWR1 phenocopies IWP2, a small molecule antagonist that inhibits the essential Wnt pathway component porcupine, IWR1 also blocks expression of known Wnt pathway targets, and effects of IWR1 can be rescued by application of LiCl, a chemical that stabilizes β-catenin. Because porcupine operates in both canonical and noncanonical Wnt signaling, comparing IWR1 and IWP2 effects could aid in differentiating the two pathways. More than a tonic for developmental biologists, IWR1 may also prove to be a valuable reagent for studying β-catenin–related human diseases.
Reinvigorating RNA transfection (A Method for Stabilizing RNA for Transfection That Allows Control of Expression Duration by Toshinori Hayashi, Deepak A. Lamba, Amber Slowik, Thomas A. Reh, and Olivia Bermingham-McDonogh, Dev Dyn239:2034–2040) Compared with DNA and viral transfection, the most common methods for gene overexpression, RNA transfection offers some significant advantages. Because RNA need only enter the cytoplasm, it is easily taken up by cells, and with the transcription step eliminated, protein production is rapid. However, RNA is unstable, making it most useful for brief pulses of gene overexpression. Here, Hayashi et al. take a cue from Venezuelan equine encephalitis virus (VEEV), which has evolved elements in the 3′untranslated region (UTR) that stabilize mRNA. The authors created a modulatable expression system, the StabiLized UTR approach (SLU), where addition of two stabilizing repeats extend an mRNA's lifespan from 6 to 24 hr, and four repeats extend it to 36 hr. The system works in a variety of cell types including embryonic stem cells, and in tissues that are notoriously difficult to transfect, like the organ of Corti. Importantly, they show that transfected Atoh1 mRNA transforms cochlear greater epithelial ridge (GER) cells to hair cells, demonstrating the functionality of SLU. For those looking for ways to boost gene overexpression, it is time to re-think RNA.
Developing diversity (Single-Cell Analysis of Somatotopic Map Formation in the Zebrafish Lateral Line System by Akira Sato, Sumito Koshida, and Hiroyuki Takeda, Dev Dyn239:2058–2065) A single ganglion harbors a diversified workforce, where individual neurons innervate discrete targets, ultimately contributing to the complex circuitry of the nervous system. With an eye toward understanding mechanisms responsible for such diversification, Sato et al. closely examined neuronal behaviors in the accessible zebrafish posterior lateral line (PLL). In the developing PLL, the primordium sequentially deposits six to eight neuromasts—each comprised of 20–30 cells—that become innervated by sensory neurons from the rostrally localized PLL ganglion. Based on close observation of live, labeled single PLL ganglion neurons, the authors identify two types. Growth cones of Type A neurons grow quickly, and have a complex network of extending filopodia relative to Type B. In addition, Type A growth cones comigrate with the primordium whereas Type B lags behind, giving A characteristics of pioneer axons and B of followers. Retrograde labeling also reveals differences in organization of cell bodies in the ganglion. Whereas Type A and B neurons are intermixed, among Type B, cell bodies are arranged such that their order reflects the relative positions of the neuromasts they innervate. This ganglion somatotopy among Type B neurons is organized as early as 54 days postfertilization, just 6 hr after deposition of the last neuromast. The authors discuss possible molecular mechanisms that drive diversity within the PLL ganglion, their next realm of inquiry.