“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.
Mysterious messages (New Meaning in the Message: Noncoding RNAs and Their Role in Retinal Development by Nicole A. Rapicavoli and Seth Blackshaw, Dev Dyn238:2103-2114) “The notion that a worm with fewer than 1,000 cells would use a scarcely larger number of genes than an organism [humans] with over 1015 cells … would have seemed laughable over a decade ago.” The statement is a compelling start to this review about noncoding RNAs (ncRNAs), which help reconcile the so-called “gene number paradox” through their ability to regulate gene expression, stability, and function. The review combines general and retina-specific information about two main ncRNA classes, microRNAs (miRNAs) and long, mRNA-like ncRNAs, whose mechanisms of action are largely unknown. Particularly intriguing is the retina-enriched miRNA cluster, miR-96/182/183, transcription of which is light-sensitive in the adult. Microphthalmia-associated transcription factor (MITF), required for retinal pigment epithelium development, is under regulation of miR-96 and 182, but additional targets and functional roles await discovery. Another surprising revelation is that ncRNAs Xist and Tsix, well-known regulators of X chromosome inactivation, are expressed dynamically in the developing retina. Based on published works, the authors speculate on possible cell-specific functions. The numerous examples cited in the review illustrate how ncRNAs may achieve developmental- and tissue-specific effects.
Making contacts (Dynamic Cell Shapes and Contacts in the Developing Drosophila Retina Are Regulated by the Ig Cell Adhesion Protein Hibris by Bree K. Grillo-Hill, and Tanya Wolff, Dev Dyn238:2223-2234) Whether you are talking about a businessman or a cell, contacts have undisputed value. They offer stability, open lines of communication, and help an individual to take shape and grow. With this in mind, Grillo-Hill and Wolff carefully depict the complex contacts made between the four cone cells in the developing Drosophila ommatidia. The anterior and posterior (A/P) cone cell pair connects in late larval development, and lose contact in the early pupae. At approximately the same time, the polar and equatorial (Po/Eq) pair makes contact. Roughly accompanying the contact transition, cells change shape from a rounded to ellipsoid morphology, with the A/P pair lagging behind the Po/Eq pair. To understand molecular mechanisms behind cone cell contact negotiations, the authors investigated the role of Hibris (Hbs), a homolog of the Nephrin receptor and part of the immunoglobulin superfamily of cell adhesion molecules. hbs alleles display a variety of phenotypes characterized by abnormal contacts, failure to make or break contacts, and aberrant cell morphology. Mosaic analysis demonstrates that hbs works cell-autonomously to promote wild-type contacts. Other phenotypes are also described, including mispatterning of the interommatidial lattice and thoracic michrochaete, and misaligned wing hairs. The potential significance of contact switching is discussed, and includes resistance to physical stresses and a contribution to overall retina morphogenesis. Breaking contacts can be just as important as making them.
Cherry on top (The Flk1-myr::mCherry Mouse as a Useful Reporter to Characterize Multiple Aspects of Ocular Blood Vessel Development and Disease by Ross A. Poche, Irina V. Larina, Melissa L. Scott, Jennifer E. Saik, Jennifer L. West, and Mary E. Dickinson, Dev Dyn238:2318-2326) Traditionally, analysis of ocular vessels in development and disease has been limited to static, fixed tissue. Here, imaging guru Mary Dickinson and colleagues show how illuminating the expression of Flk1-myr::mCherry in live, transgenic mice can be. The utility of the line, a myristoylated mCherry fluorescent protein expressed in endothelial cells (ECs), is revealed through pilot studies in the eye s three vascular beds: the embryonic hyaloid arterial vessels, which undergo apoptosis in early postnatal stages, retinal vessels, and choroidal vessels that encircle the outer optic cup. Their work shows various ways the line can be used. (1) Clear labeling of diminishing hyaloid vessels and EC debris engulfed by macrophages demonstrate its usefulness in studying vessel apoptosis. (2) High speed imaging successfully captures the flow of green fluorescent protein-labeled blood cells within mCherry-labeled vessels show its effectiveness for analyzing vessel hemodynamics. (3) Three-dimensional confocal analysis of retinal vessels illustrate the line s value for examining vessel morphology. (4) Successful labeling of neovessels induced by vascular endothelial growth factor-releasing hydrogels inserted into the cornea demonstrates a new way to screen for pro- and anti-angiogenic factors. The cherry on top is that the tissue in which all these assays can be performed is easily accessible.