“Highlights” is a feature that 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.
Do the Strand (Dev Dyn 2007;236:84–92) In this Special Focus Research Article on the enteric nervous system (ENS), Druckenbrod and Epstein describe behaviors of migratory enteric neural crest-derived cells (ENCCs) as they populate the ENS. ENCCs follow a wavefront where connected chains of cells, or strands, form and extend to the gut mesenchyme. Using time-lapse imaging in chick and mice, the authors document how three cell types, distal, rostral, and anterior cells (DCs, RCs, ACs), influence overall strand dynamics. DCs, the leading cells of strands, are exploratory, extending filopodia and changing trajectories during their rostral to caudal route. RC dynamics vary with respect to distance from the wavefront; they chiefly elongate and maintain the integrity of strands. ACs play a prominent role in colonization of the cecum and proximal colon. Like RCs, they elongate strands, and also influence DC trajectories. Potential mechanisms that guide the intricate strand cell dance are discussed.
Time Is of the Essence (Dev Dyn 2007;236:142–155) Most are familiar with the concept that circadian rhythms dictate when you are prone to feeling sleepy or wakeful. But did you know that the cell cycle in proliferating bone marrow is also synchronized to day–night cycles? These facts and much more are brought to light in this compelling review on circadian rhythm. The article not only covers the molecular bases and physiological outputs of circadian rhythm, but also development of circadian timing and the impact of development on the circadian clock. Is early embryonic development also under the spell of day–night rhythms? Read the review to find out.
Going Gray (Dev Dyn 2007;236:282–289) It is tempting to blame newfound gray hairs on mounting stresses at work. This paper highlights another possible cause, malfunctioning Notch receptors. During hair growth, melanocytes deliver pigment to the hair matrix. As the melanocyte stem cell population is depleted, hair pigmentation decreases, producing gray hair. The authors show that mice with a conditional deletion of Notch 1 or 2 from melanocytes undergo premature graying; eye pigmentation is unaffected. Moreover, graying is dose-dependent; it is accelerated upon deletion of additional Notch1/2 alleles. The underlying defect is precocious depletion of Dct-expressing cells, which labels melanoblasts and melanocytes. This work suggests that Notch 1 and 2 have overlapping functions in regulating self-renewal of hair follicle melanocyte stem cells.