“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.
Regulating the regulators' regulators (Epigenetic Regulation of Cardiac Development and Function by Polycomb Group and Trithorax Group Proteins by Q. Tian Wang, Dev Dyn 2012;241:1021–1033). Epigenetics is all about regulating the regulators. Histone modifying proteins, chromatin remodelers, and the like, alter gene expression by making stretches of chromatin accessible or inaccessible to gene regulators. Polycomb Group (PcG) and Trithorax Group (TrxG) proteins are known for maintaining activated or repressed chromatin states for extended periods of time. It may seem surprising, then, that these regulators of “cellular memory” are dynamic regulators. Yet in this review, Wang carefully details the evidence that they do just that in the developing heart. A good example: inactivation of Polycomb Repressor Complex 2 (PRC2) core subunits, Ezh2 or Eed, in various heart cell populations and/or at slightly different times in development triggers complex but distinct defects. The results suggest PRC2 is required for many aspects of heart morphogenesis throughout development. In another case, the TrxG protein Brg can be activated by stress in the adult heart, and is essential for development of induced hypertrophy, suggesting it might play a role in heart disease. Both examples illustrate the flexibility of these chromatin regulators and suggest that PcG and TrxG proteins are poised to alter expression of multiple genes in response to developmental and physiological cues.
Expanding possibilities (Optic Tectum Morphogenesis: A Step-by-Step Model Based on the Temporal–Spatial Organization of the Cell Proliferation. Significance of Deterministic and Stochastic Components Subsumed in the Spatial Organization by Melina Rapacioli, Santiago Duarte, Alejandra Rodríguez Celín, Luciano Fiore, Luisa Teruel, Gabriel Scicolone, Viviana Sanchez, and Vladimir Flores, Dev Dyn 2012;241:1043–1061) During its proliferative phase, the chick optic tectum (OT), as seen in dorsal–ventral sections, grows from a small kidney bean shape to a large heart-like shape, where the rounded side of the bean dives in to divide the lobes of the heart. The work presented here tackles the question of whether cell proliferation in the neuroepithelium (NE) shapes the developing optical tectum. Measurements that document the spatiotemporal profile of mitotic NE cells and their densities demonstrate an asymmetric zone of high mitotic density (zHMD) that shifts over time. At the morphogenic level, the zHMD contributes to an initial dorsal curvature and later lateral protrusion. Statistical analyses of multiple features suggest that these morphogenetic changes are in part based on a long-range deterministic component and on a short-range stochastic component that encompasses local influences such as synchronization between neighboring cells. Together these data demonstrate the power of biomathematical modeling in revealing insights into mechanisms of developmental processes.