Editorial highlights

Every organism is a model organism for understanding development, evolution, disease, and regeneration, and we have only begun to scratch the surface of the interdisciplinary genetic, molecular, cellular, and developmental mechanisms that regulate these biological processes. These “Highlights” denote exciting advances recently reported in Developmental Dynamics that illustrate the complex dynamics of developmental biology.

Organogenesis—Lung Biology “Evolving topological order in the postnatal visceral pleura” by Betty Liu, Ali Ali, Stacey Kwan, Jennifer Pan, Willi Wagner, Hassan Khalil, Zi Chen, Maximilian Ackermann, and Steven Mentzer; Dev Dyn 253:8, pp. 711–721. https://doi.org/10.1002/dvdy.688. The surface of a visceral organ is lined by layers of epithelial cells that provide a selective barrier to the surrounding environment. Within these layers, epithelial cells exhibit complex shapes characterized by the number of sides adjoining neighboring cells, and polygonal shapes are associated with optimal cell packing and minimal free surface energy. Proper development of the lung requires rapid growth during the postnatal period with physical interactions between the visceral pleura and subjacent alveoli, which are exposed to both static and dynamic forces that influence cell shape and orientation. In this study, the authors investigated postnatal lung development discovering a high degree of network heterogeneity in which a small number of highly connected nodes, or hubs, play crucial roles in maintaining the network's structural integrity. Furthermore, this facilitated efficient information flow during the challenges of rapid lung growth. Taken together, changes in epithelial cell shape reflect optimal cell packing and the minimization of surface free energy, but also cell–cell interactions, cell proliferation, and cytoskeletal rearrangements, each of which is critical for normal lung development.

Organogenesis—Cochlea Development “Localization of cadherins in the postnatal cochlear epithelium and their relation to space formation” by Holly Beaulac and Vidhya Munnamalai; Dev Dyn 253:8, pp. 771–780. https://doi.org/10.1002/dvdy.692. The cochlea is a fluid-filled spiral cavity within the inner ear, that contains the organ of Corti. Comprised of three rows of outer hair cells and one row of inner hair cells in humans, the organ of Corti produces nerve impulses in response to sound vibrations. The organ of Corti has therefore been called the “temple of hearing” in the inner ear. The sensory epithelium in the organ of Corti consists of mechanosensory hair cells intercalated by epithelial support cells. The support cells are stiff yet compliant enough to withstand and modulate vibrations to the hair cells, and the cell adhesion properties of adjoining cell membranes between cells are flexible to allow the formation of fluid-filled spaces within the cochlea. This study investigated the role of cadherins, typically associated with cytoskeletal remodeling, in cochlea development and discovered that extensive F-actin remodeling occurs within the first week of birth. Furthermore, transient changes in cytoskeletal F-actin influence epithelial morphogenesis, and changes in the strength and properties of cell adhesion drive the formation of fluid-filled spaces in the epithelium that are central for proper hearing.

Neural Development “Requirement of a novel gene, drish, in the zebrafish retinal ganglion cell and primary motor axon development” by Suman Gurung, Nicole Restrepo, Surendra Kumar Anand, Vinoth Sittaramane, and Saulius Sumanas; Dev Dyn 253:8, pp. 750–770. https://doi.org/10.1002/dvdy.694. During nervous system development, a motor neuron's axons traverse the extracellular matrix to make synaptic connections, which are critical for neural circuit function. Zebrafish possess two distinct classes of spinal motor neurons: primary and secondary. This study explores the activity and functional role of a novel putative transmembrane protein, Drish, in zebrafish. Loss-of-function mutant embryos exhibit defects in retinal ganglion cell differentiation, with thinner optic nerves, and abnormal branching of motor neurons. In addition, drish mutant adults exhibit deficiencies in the outer nuclear layer of the retina and consequently display defective light response and locomotory behaviors. Drish may function downstream of Hh signaling, however, the exact role of Drish requires further investigation. This study therefore reveals the important roles of drish in retinal ganglion cell, optic nerve and interneuron development, and in spinal motor axon branching in zebrafish.