Dynamic morphogenesis of a pioneer axon in Drosophila and its regulation by Abl tyrosine kinase.

The fundamental problem in axon growth and guidance is to understand how cytoplasmic signaling modulates the cytoskeleton to produce directed growth cone motility. We here dissect this process using live imaging of the TSM1 axon of the developing Drosophila wing. We find that the growth cone is almost purely filopodial, and that it extends by a protrusive mode of growth. Quantitative analysis reveals two separate groups of growth cone properties that together account for growth cone structure and dynamics. The core morphological features of the growth cone are strongly correlated with one another and define two discrete morphs. Genetic manipulation of a critical mediator of axon guidance signaling, Abelson (Abl) tyrosine kinase, shows that while Abl weakly modulates the ratio of the two morphs it does not greatly change their properties. Rather, Abl primarily regulates the second group of properties, which report the organization and distribution of actin in the growth cone and are coupled to growth cone velocity. Other experiments dissect the nature of that regulation of actin organization and how it controls the spatial localization of filopodial dynamics and thus axon extension. Together, these observations suggest a novel, probabilistic mechanism by which Abl biases the stochastic fluctuations of growth cone actin to direct axon growth and guidance.

Expression of a Fragment of Ankyrin 2 Disrupts the Structure of the Axon Initial Segment and Causes Axonal Degeneration in Drosophila.

Neurodegenerative stimuli are often associated with perturbation of the axon initial segment (AIS), but it remains unclear whether AIS disruption is causative for neurodegeneration or is a downstream step in disease progression. Here, we demonstrate that either of two separate, genetically parallel pathways that disrupt the AIS induce axonal degeneration and loss of neurons in the central brain of Drosophila. Expression of a portion of the C-terminal tail of the Ank2-L isoform of Ankyrin severely shortens the AIS in Drosophila mushroom body (MB) neurons, and this shortening occurs through a mechanism that is genetically separate from the previously described Cdk5α-dependent pathway of AIS regulation. Further, either manipulation triggers morphological degeneration of MB axons and is accompanied by neuron loss. Taken together, our results are consistent with the hypothesis that disruption of the AIS is causally related to degeneration of fly central brain neurons, and we suggest that similar mechanisms may contribute to neurodegeneration in mammals.

MicroRNA-mediated disruption of dendritogenesis during a critical period of development influences cognitive capacity later in life.

The prenatal period of cortical development is important for the establishment of neural circuitry and functional connectivity of the brain; however, the molecular mechanisms underlying this process remain unclear. Here we report that disruption of the actin-cytoskeletal network in the developing mouse prefrontal cortex alters dendritic morphogenesis and synapse formation, leading to enhanced formation of fear-related memory in adulthood. These effects are mediated by a brain-enriched microRNA, miR-9, through its negative regulation of diaphanous homologous protein 1 (Diap1), a key organizer of the actin cytoskeletal assembly. Our findings not only revealed important regulation of dendritogenesis and synaptogenesis during early brain development but also demonstrated a tight link between these early developmental events and cognitive functions later in life.

Diagnostic Evaluation of Nontraumatic Chest Pain in Athletes.

This article is a clinically relevant review of the existing medical literature relating to the assessment and diagnostic evaluation for athletes complaining of nontraumatic chest pain. The literature was searched using the following databases for the years 1975 forward: Cochrane Database of Systematic Reviews; CINAHL; PubMed (MEDLINE); and SportDiscus. The general search used the keywords chest pain and athletes. The search was revised to include subject headings and subheadings, including chest pain and prevalence and athletes. Cross-referencing published articles from the databases searched discovered additional articles. No dissertations, theses, or meeting proceedings were reviewed. The authors discuss the scope of this complex problem and the diagnostic dilemma chest pain in athletes can provide. Next, the authors delve into the vast differential and attempt to simplify this process for the sports medicine physician by dividing potential etiologies into cardiac and noncardiac conditions. Life-threatening causes of chest pain in athletes may be cardiac or noncardiac in origin, which highlights the need for the sports medicine physician to consider pathology in multiple organ systems simultaneously. This article emphasizes the importance of ruling out immediately life threatening diagnoses, while acknowledging the most common causes of noncardiac chest pain in young athletes are benign. The authors propose a practical algorithm the sports medicine physician can use as a guide for the assessment and diagnostic work-up of the athlete with chest pain designed to help the physician arrive at the correct diagnosis in a clinically efficient and cost-effective manner.

Inherited Variants in SULT1E1 and Response to Abiraterone Acetate by Men with Metastatic Castration Refractory Prostate Cancer.

PURPOSE: Germline variations in genes involved in androgen biosynthesis and metabolic pathways may predict the response to abiraterone acetate in men with metastatic, castration refractory prostate cancer. The variations may serve as prognostic and predictive biomarkers to allow for more individualized therapy. MATERIALS AND METHODS: We evaluated 832 single nucleotide polymorphisms from the OmniExpress genotyping platform (Illumina®) in the boundaries of 61 candidate genes reported to be involved in the androgen metabolic pathway. The purpose was to investigate them for an association with time to treatment failure in 68 white men with metastatic, castration refractory prostate cancer undergoing treatment with abiraterone acetate. Cox proportional hazard analysis was used with Gleason score, age, level of alkaline phosphatase and prostate specific antigen at treatment initiation as covariates. Each single nucleotide polymorphism was assessed using an allele carriage genetic model in which carriage of 1 or more minor alleles contributes to increased risk. Subset analyses were done to determine whether metastasis site, or prior treatment with ketoconazole or docetaxel would interact with the single nucleotide polymorphisms investigated. RESULTS: Six single nucleotide polymorphisms in the estrogen sulfotransferase gene SULT1E1 were associated with time to treatment failure on abiraterone acetate therapy after false discovery rate (q value) correction for multiple testing while controlling for Gleason score, age, level of alkaline phosphatase and prostate specific antigen at treatment initiation (q <0.05). CONCLUSIONS: Single nucleotide polymorphisms in SULT1E1 were significantly associated with time to treatment failure in men on abiraterone acetate therapy. The single nucleotide polymorphisms may serve as predictive markers for treatment with abiraterone acetate.