“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 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.
(De)Constructing Cilia (Building it up and taking it down: The regulation of vertebrate ciliogenesis, by Nicole Santos and Jeremy F. Reiter, Dev Dyn237:1972–1981) The primary cilium is a microtubule-based sensory organelle that protrudes from the surface of nearly all cells in the body. By receiving information from outside the cell and relaying that information inside, the cilium helps the cell respond to its neighbors and environment. Multiple disorders are attributable to dysfunctional cilia including polycystic kidney disease, Bardet-Biedl syndrome, and primary ciliary dyskinesia, which is often associated with internal organ reversal. In one of six special focus reviews on the Primary Cilium, Santos and Reiter discuss the cellular processes that regulate cilium assembly and disassembly. Because ciliary microtubules emanate from the cell centriole, which is also involved in organizing the mitotic spindle, particular attention is paid to molecules that help mediate cross-talk between the two. Several proteins that function in cell cycle progression also have a role in cilium construction during G1 or deconstruction just before mitosis. Also discussed are the influence of growth factor signaling and the planar cell polarity pathway—a Wnt signaling pathway that is independent of β-catenin. The importance of primary cilia in everything from development to disease is sure to make this a field to watch.
Signal to Breathe (Role for EphrinB2 in postnatal lung alveolar development and elastic matrix integrity, by George A. Wilkinson, Johannes C. Schittny, Dieter P. Reinhardt, and Rüdigger Klein, Dev Dyn237:2220–2234) When you take a breath, oxygen travels to terminal branches in the lung, which contain millions of small outcroppings called aveoli. These structures are filled with capillaries, allowing airborne oxygen to efficiently enter the blood stream and carbon dioxide to leave. Mouse alveoli primarily develop after birth, and one major step is the formation of tissue folds, or secondary septa, that partition the lung space and eventually become the alveolar wall. How secondary septation occurs is not well understood, but it is thought to require communication between multiple cell types. Wilkinson et al., find that the ephrinB2 signaling ligand is an essential component. Mice engineered with partially functional ephrinB2 have severely disorganized lung extracellular matrix and fail to develop secondary septa and alveoli. The authors show that ephrinB2 is expressed in the developing lung and that prior to secondary septum formation, ephrinB2 expression becomes strong in the capillary beds. Also, ephrin tyrosin kinase receptors. EphB2, B3, and B4, are expressed in neighboring cells during this developmental time. Their data suggest a model whereby Eph-ephrin signaling plays a role in the cellular communication necessary for septation, and thus alveolar development.
A Time for Choosing (Notch-regulated oligodendrocyte specification from radial glia in the spinal cord of zebrafish embryos, by Ho Kim, Jimann Shin, Suhyun Kim, Justin Poling, Hae-Chul Park, and Bruce Appel,Dev Dyn237:2081–2089) During neurogenesis, neuroepithelial cells transform into radial glia, which were long thought to perform a structural function in the nervous system. However, recently it was found in mammals that some radial glia function as neural precursors. Kim et al., demonstrate that zebrafish radial glia, which are present throughout development, similarly function as neural precursors giving rise to motorneurons and myelinating oligodendrocytes in the spinal cord. Moreover, they show that notch signaling is responsible for oligodendrocyte specification and for maintaining the radial glia precursor state at early stages, but not later stages. The authors inhibit notch signaling in two different ways at specific developmental times. When signaling was reduced before oligodendrocyte formation, there was a dramatic decrease in the number of radial glia and oligodendrocyte progenitor cells and an increase in the number of motor neurons. But when notch signaling was reduced later in embryogenesis or during larval stages, there was no change in the resulting cell population. The conclusion—notch is required early, but in time, an unknown pathway takes over.