“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.
Taste test (Epibranchial Placode-Derived Neurons Produce BDNF Required for Early Sensory Neuron Development by Danielle E. Harlow, Hui Yang, Trevor Williams, and Linda A. Barlow, Dev Dyn240:309–323) In the developing gustatory system, brain-derived neurotrophic factor (BDNF) is best known for its “main course” role supporting the survival of gustatory neurons and proper innervation of peripheral targets. Here, Harlow et al. test whether BDNF is also a key ingredient for an appetizer that sets the stage for the entree. In support of this hypothesis, they demonstrate that BDNF-LacZ expression initiates in a subset of mouse geniculate ganglia (gVII) neurons at embryonic day 9.5, before previously reported BDNF expression. Within gVII, the BDNF receptor, TrkB, is expressed in placode-derived neurons, and BDNF itself in a subset of these neurons. To determine whether this apparent paracrine or autocrine BDNF signaling is important for gustatory system development, phenotypes of mice where bdnf is selectively eliminated from placodal neuroblasts were compared with bdnf knockout mice. In both cases, significant numbers of pre- and postmitotic neurons display a delay in maturation. These findings demonstrate the importance of BDNF in early gustatory neuronal development. Future work will determine how mother nature—a skilled chef—can use the same ingredients throughout the meal, but to different effects.
Getting to know noncanonical Notch (Noncanonical Notch Function in Motor Axon Guidance Is Mediated by Rac GTPase and the GEF1 Domain of Trio by Jeong K. Song and Edward Giniger, Dev Dyn240:324–332) Noncanonical Notch signaling makes the Notch pathway more nimble, enabling cross-talk with diverse regulators. During axon growth and guidance, Drosophila motor neurons rely on noncanonical Notch signaling to interact with key regulators of actin dynamics, the Rho GTPases. Notch associates with and antagonizes components of the Abl tyrosine kinase signaling pathway, including Trio, a guanine nucleotide exchange factor (GEF) for Rho GTPases. Here, Song and Giniger flesh out downstream steps of this context-dependent pathway. First, rescue experiments demonstrate that Trio's Rac-specific GEF1 domain, but not its Rho-specific GEF2 domain, is required for noncanonical Notch signaling. Consistent with the finding, constitutively active and dominant-negative Rac modulates Notch-mediated axon guidance, but manipulation of the Rho GTPases Cdc42 and Rho1 do not. Not for the faint of heart, the experiments demand only slight alterations to Trio or Rac levels, as tipping the balance too far produces combinatorial effects. The authors hypothesize that the Abl/Rac signaling network bridges Notch to actin cytoskeleton rearrangements that push and pull the axonal growth cone to its target.
Running dry (An Obesogenic Diet Started Before Puberty Leads to Abnormal Mammary Gland Development During Pregnancy in the Rabbit by Cathy Hue-Beauvais, Pascale Chavatte-Palmer, Etienne Aujean, Michéle Dahirel, Patrice Laigre, Christine Péchoux, Stephan Bouet, Eve Devinoy, and Madia Charlier, Dev Dyn240:347–356) Health risks to the obese—frequently caused by high fat, high sugar diets during adolescence—are well established. But the impact of obesity on the next generation is just beginning to be understood. Here, Hue-Beauvais and colleagues investigate physiological reasons behind reports that obese women are less likely to breastfeed, by examining mammary gland development in obese rabbits. At mid-pregnancy, rabbits fed an obesogenic (OD) diet before puberty display precocious development of mammary gland alveolar structures. Electron microscopy and Western analysis further show that ducts are prematurely filled with milk proteins and lipids. The data suggest that the observed premature mammary growth and differentiation potentially leads to dysregulation of post-partum lactation. Of interest, the authors also note that pups from mid-gestation OD mothers are significantly underweight, possibly due to decreased placental efficiency. Follow-up work may substantiate these effects on future generations, fueling the need for putting a stop to childhood obesity.