Neuroscience. Crossing the midline

Diffusion tensor imaging and fiber tractography in brain malformations

Diffusion tensor imaging (DTI) is an advanced MR technique that provides qualitative and quantitative information about the micro-architecture of white matter. DTI and its post-processing tool fiber tractography (FT) have been increasingly used in the last decade to investigate the microstructural neuroarchitecture of brain malformations. This article aims to review the use of DTI and FT in the evaluation of a variety of common, well-described brain malformations, in particular by pointing out the additional information that DTI and FT renders compared with conventional MR sequences. In addition, the relevant existing literature is summarized.

Guidance for life, cell death, and colorectal neoplasia by netrin dependence receptors

This review is focusing on a critical mediator of embryonic and postnatal development with multiple implications in inflammation, neoplasia, and other pathological situations in brain and peripheral tissues. These morphogenetic guidance and dependence processes are involved in several malignancies targeting the epithelial and immune systems including the progression of human colorectal cancers. We consider the most important findings and their impact on basic, translational, and clinical cancer research. Expected information can bring new cues for innovative, efficient, and safe strategies of personalized medicine based on molecular markers, protagonists, signaling networks, and effectors inherent to the Netrin axis in pathophysiological states.

Recognition molecules and neural repair

Neural recognition molecules were discovered and characterized initially for their functional roles in cell adhesion as regulators of affinity between cells and the extracellular matrix in vitro. They were then recognized as mediators or co-receptors which trigger signal transduction mechanisms affecting cell adhesion and de-adhesion. Their involvement in contact attraction and repulsion relies on cell-intrinsic properties that are modulated by the spatial contexts of their expression at particular stages of ontogenetic development, in synaptic plasticity and during regeneration after injury. The functional roles of recognition molecules in cell proliferation and migration, determination of developmental fate, growth cone guidance, and synapse formation, stabilization and modulation have been well documented not only by in vitro, but also by in vivo studies that have been greatly aided by generation of genetically altered mice. More recently, the functions of recognition molecules have been investigated under conditions of neural repair and manipulated using a broad range of genetic and pharmacological approaches to achieve a beneficial outcome. The principal aim of most therapeutically oriented approaches has been to neutralize inhibitory factors. However, less attention has been paid to enhancing repair by stimulating the stimulatory factors. When considering potential therapeutic strategies, it is worth considering that a single recognition molecule can possess domains that are conducive or repellent and that the spatial distribution of recognition molecules can determine the overall function: Recognition molecules may be repellent for neurite outgrowth when presented as barriers or steep-concentration gradients and conducive when presented as uniform substrates. The focus of this review will be on the more recent attempts to study the conducive mechanisms with the expectation that they may be able to tip the balance from a regeneration inhospitable to a hospitable environment. It is likely that a combination of the two principles, as multifactorial as each principle may be in itself, will be of therapeutic value in humans.

Minireview: recent progress in gonadotropin-releasing hormone neuronal migration

Neurons that synthesize GnRH are critical brain regulators of the reproductive axis, yet they originate outside the brain and must migrate over long distances and varied environments to get to their appropriate positions during development. Many studies, past and present, are providing clues for the types of molecules encountered and movements expected along the migratory route. Recent studies provide real-time views of the behavior of GnRH neurons in the context of in vitro preparations that model those in vivo. Live images provide direct evidence of the changing behavior of GnRH neurons in their different environments, showing that GnRH neurons move with greater frequency and with more alterations in direction after they enter the brain. The heterogeneity of molecular phenotypes for GnRH neurons likely ensures that multiple external factors will be found that regulate the migration of different portions of the GnRH neuronal population at different steps along the route. Molecules distributed in gradients both in the peripheral olfactory system and basal forebrain may be particularly influential in directing the appropriate movement of GnRH neurons along their arduous migration. Molecules that mediate the adhesion of GnRH neurons to changing surfaces may also play critical roles. It is likely that the multiple external factors converge on selective signal transduction pathways to engage the mechanical mechanisms needed to modulate GnRH neuronal movement and ultimately migration.

Roles of glia in the Drosophila nervous system

Glial cells have diverse functions that are necessary for the proper development and function of complex nervous systems. Various insects, primarily the fruit fly Drosophila melanogaster and the moth Manduca sexta, have provided useful models of glial function during development. The present review will outline evidence of glial contributions to embryonic, visual, olfactory and wing development. We will also outline evidence for non-developmental functions of insect glia including blood-brain-barrier formation, homeostatic functions and potential contributions to synaptic function. Where relevant, we will also point out similarities between the functions of insect glia and their vertebrate counterparts.

Attraction or repulsion: a matter of individual taste?

Cell migration along the correct paths is critical to normal organogenesis and tissue repair, and goes awry in tumor dissemination. Understanding the molecular cues that control such migration would provide opportunities to control these events. Recent findings in Drosophila highlight the role of the epidermal growth factor receptor (EGFR) in chemotaxis and pathfinding during development. These studies, and others performed in vertebrates, support a central role for EGFR-mediated chemotaxis. However, the signal or signals that then enable cells to further migrate independently of this chemotactic effect are not known. Three possible scenarios are discussed: that EGFR signaling sensitizes cells to new cues, that EGFR signaling is altered so that the cell responds predominantly to other motility signals that are now "unblinded," and that EGFR signaling still provides the motile signal but in a chemokinetic manner with matrix components providing the directionality. There are precedents for all three scenarios, but which one proves true will define the window of opportunity for regulating cell migration.