Highlights in DD

Abstract

“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. Not too late to remodel (Rapid Remodeling of Airway Vascular Architecture at Birth by Amy Ni, Erin Lashnits, Li-Chin Yao, Peter Baluk, and Donald M. McDonald, Dev Dyn 239:2354–2366) When form ceases to support function, it is time to remodel. Ni et al. discover that the mantra is not limited to kitchens and homes; tracheal vasculature also follows the same principle. Using the trachea as an easily studied representative of the airways, they document that embryonic day (E) 17.5 mice have a web-like primitive tracheal vascular plexus that is reminiscent of vascular architecture in the yolk sac. During postnatal stages P0–P3, an astounding 76% the vascular network is pruned, leaving a skeleton of vasculature that grows horizontally over the ladder-like cartilage rings lining the trachea. At P4, horizontal capillaries re-grow, and arterioles and venules begin to grow vertically between the rings, acquiring most features of adult vasculature by P7. Of interest, the vasculature of kidney, brain, and liver, all fail to undergo a similar overhaul at birth, suggesting that exposure to atmospheric oxygen may contribute to the remodeling phenomenon in the trachea. While the hypothesis remains to be tested, the authors do identify other mechanisms associated with vascular regression and re-growth. Hypoxic regions and hypoxia inducible factor (HIF1-α) correlate with vessel survival after birth, and survival of tracheal vasculature from P0 to P7 is dependent upon vascular endothelial growth factor (VEGF). Future work will focus on the roles of signaling pathways and changes in oxygen tension on vascular remodeling during postnatal development and disease. Smart screen (Essential Genes for Astroglial Development and Axon Pathfinding During Zebrafish Embryogenesis by Michael J.F. Barresi, Sean Burton, Kristina Dipietrantonio, Adam Amsterdam, Nancy Hopkins, and Rolf O. Karlstrom, Dev Dyn 239:2603–2618) Astroglia are the unsung heroes of neural development. Once believed to function solely as scaffold support for neurons, it is now understood that they play wide-ranging roles during neurogenesis such as in forming the blood–brain barrier, neural patterning, and regeneration. Despite their universal importance, little is known about astroglial development. To remedy this oversight, the authors screened an existing zebrafish mutant collection, for which the affected genes were already identified. They describe 25 mutants that are placed into one or more categories: axonal pathfinding, gliogenesis, glial patterning and neurogenesis. One important observation is that defects in glial patterning correlate with perturbed axon pathfinding, suggesting axon–glial interactions are important for axon scaffold formation. Another is the discovery of a new class of mutants affecting cell number of radial glial cells, the main source of neural stem cells in vertebrate embryos. The work also identifies potential novel roles for the affected genes, many of which are familiar signaling pathway components or transcription factors (i.e., chordin, tbx16). These intriguing preliminary findings double as jumping-off points from which to further the understanding of brain development. Green eggs and sperm (The ziwi Promoter Drives Germline-Specific Gene Expression in Zebrafish by David H. Leu and Bruce W. Draper, Dev Dyn 239:2714–2721) Here Leu and Draper unveil a tool that will be of interest to germ cell researchers and the zebrafish community at-large. They show that a 4.8-kb promoter of ziwi, which encodes an Argonaut class protein involved in Piwi-interacting RNA (piRNA) metabolism, can drive germline-specific, heterologous gene expression. Expression of the Tg(ziwi:EGFP) transgene initiates at 7 days postfertilization (dpf) in bipotential gonocytes and continues to be expressed after the onset of sexual differentiation (18–21 dpf) in all testis and ovary germ cells. Demonstrating the utility of the tool as a germ cell marker, Tg(ziwi:EGFP) aids the authors in defining new substages in stage-1A oocytes. What sets this germline-specific transgene apart from others, however, is that it is reliably expressed in premeiotic oocytes. The authors discuss the potential utility of the ziwi promoter in manipulating gene expression in the germline, producing genetic mosaic germlines, and speculate how the tool could propel the future of germ cell related technologies in zebrafish.