“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.
Growth Spurts (Dev Dyn236:2668–2674) Just when you thought that Generation Y was primarily concerned with iPods, cell phones, and Facebook, a star like 17-year-old Isha Jain comes shining through. Jain is first author of the paper presented here, which helped her earn Grand Prize in the prestigious Siemens Competition in Math, Science, and Technology for US high school students. Zebrafish fins grow by the sequential addition of bony segments at the distal end, but their manner of growth has been under dispute. In collaboration with her colleagues, and mentor M. Kathryn Iovine, PhD, Jain shows that segment growth is achieved by multiple cell proliferation saltations, or pulses. The number of bromodeoxyuridine (S-phase) and H3P (mitosis) -positive mesenchymal cells per segment were counted in 12- to 14-week-old fish, and their distance from the distal end measured. The resulting graphs clearly show jumps in cell numbers at approximately 60-am intervals, a finding supported by statistical analysis. Of interest, cells across segments express the gene-based growth marker fa93e10, suggesting that even periods yielding few dividing cells are part of an overall growth cycle, and saltations are subject to extracellular cues. Jain will be one to watch, particularly if she is in the midst of an intellectual growth cycle.
Beware, Cellular Mimicry (Dev Dyn236:3199–3207) Any ecologist knows that when an individual from one species appears like that of another species, it is called mimicry. In this eye-opening review from the Stem Cells Special Issue, Angie Rizzino, PhD, says it is imperative that developmental biologists also become familiar with the concept. Before a cell can transdifferentiate into a cell type from another developmental lineage, it must overcome several hurdles. The proper battery of genes must be expressed at appropriate levels, while others are silenced or epigenetically “poised” for expression. Rizzino argues that, in many reported studies, rather than bona fide transdifferentiation, it is more likely that cells undergo cellular mimicry: they have the appearance of a desired cell type, but their molecular signature is mosaic. Indeed, identities of “transdifferentiated” cells are rarely verified with comprehensive analysis, including extensive gene and epigenetic profiling, and in vivo functional testing. Whether cells truly transdifferentiate in certain circumstances is a question that must be resolved before they can be used in a therapeutic context.
Quantum Dot Mechanics (Dev Dyn236:3393–3401) Although the term Quantum Dots (QDs) sounds like something out of Star Trek, they are today's reality. The inorganic fluorophores are tiny (b25 nm), exceptionally photostable, have a broad absorption and narrow emission spectra, and can be functionalized by cross-linking bioactive molecules. Slotkin et al. thought this skill set made QDs an ideal candidate for labeling mammalian progenitor cells in vivo, but methods for introducing them directly into the body's stem cells remained elusive. To solve this problem, the authors used two techniques to effectively deliver QDs to neural stem and progenitor cells (NSPCs) in the early mouse embryo in utero: ultrasound guided biomicroscopy (UBM) injection, and electroporation. QD-labeled NSPCs appear to migrate and differentiate normally as wild-type. In vitro experiments demonstrate that cell survival and oxidative stress are also normal. Remarkably they also show that, when embryos were labeled at the one-to two-cell stage, apparently all descendants remain labeled until at least embryonic day 13.5. Methods using QDs, like fluorescence resonance energy transfer (FRET), cell lineage tracing, or delivery of therapeutic molecules will follow on the heels of their successes, bringing mammalian embryology to the 21st (or 23rd?) century.