Growth, guidance and branching of axons are all essential processes for the precise wiring of the nervous system. Rho family GTPases transduce extracellular signals to regulate the actin cytoskeleton. In particular, Rac has been implicated in axon growth and guidance. Here we analyse the loss-of-function phenotypes of three Rac GTPases in Drosophila mushroom body neurons. We show that progressive loss of combined Rac1, Rac2 and Mtl activity leads first to defects in axon branching, then guidance, and finally growth. Expression of a Rac1 effector domain mutant that does not bind Pak rescues growth, partially rescues guidance, but does not rescue branching defects of Rac mutant neurons. Mosaic analysis reveals both cell autonomous and non-autonomous functions for Rac GTPases, the latter manifesting itself as a strong community effect in axon guidance and branching. These results demonstrate the central role of Rac GTPases in multiple aspects of axon development in vivo, and suggest that axon growth, guidance and branching could be controlled by differential activation of Rac signalling pathways.

Mutations in gigaxonin were identified in giant axonal neuropathy (GAN), an autosomal recessive disorder. To understand how disruption of gigaxonin's function leads to neurodegeneration, we ablated the gene expression in mice using traditional gene targeting approach. Progressive neurological phenotypes and pathological lesions that developed in the GAN null mice recapitulate characteristic human GAN features. The disruption of gigaxonin results in an impaired ubiquitin-proteasome system leading to a substantial accumulation of a novel microtubule-associated protein, MAP8, in the null mutants. Accumulated MAP8 alters the microtubule network, traps dynein motor protein in insoluble structures and leads to neuronal death in cultured wild-type neurons, which replicates the process occurring in GAN null mutants. Defective axonal transport is evidenced by the in vitro assays and is supported by vesicular accumulation in the GAN null neurons. We propose that the axonal transport impairment may be a deleterious consequence of accumulated, toxic MAP8 protein.

Disruption of the BPAG1 (bullous pemphigoid antigen 1) gene results in progressive deterioration in motor function and devastating sensory neurodegeneration in the null mice. We have previously demonstrated that BPAG1n1 and BPAG1n3 play important roles in organizing cytoskeletal networks in vivo. Here, we characterize functions of a novel BPAG1 neuronal isoform, BPAG1n4. Results obtained from yeast two-hybrid screening, blot overlay binding assays, and coimmunoprecipitations demonstrate that BPAG1n4 interacts directly with dynactin p150Glued through its unique ezrin/radixin/moesin domain. Studies using double immunofluorescent microscopy and ultrastructural analysis reveal physiological colocalization of BPAG1n4 with dynactin/dynein. Disruption of the interaction between BPAG1n4 and dynactin results in severe defects in retrograde axonal transport. We conclude that BPAG1n4 plays an essential role in retrograde axonal transport in sensory neurons. These findings might advance our understanding of pathogenesis of axonal degeneration and neuronal death.

Neurons undergo extensive morphogenesis during development. To systematically identify genes important for different aspects of neuronal morphogenesis, we performed a genetic screen using the MARCM system in the mushroom body (MB) neurons of the Drosophila brain. Mutations on the right arm of chromosome 2 (which contains ~20% of the Drosophila genome) were made homozygous in a small subset of uniquely labeled MB neurons. Independently mutagenized chromosomes (4600) were screened, yielding defects in neuroblast proliferation, cell size, membrane trafficking, and axon and dendrite morphogenesis. We report mutations that affect these different aspects of morphogenesis and phenotypically characterize a subset. We found that roadblock, which encodes a dynein light chain, exhibits reduced cell number in neuroblast clones, reduced dendritic complexity and defective axonal transport. These phenotypes are nearly identical to mutations in dynein heavy chain Dhc64 and in Lis1, the Drosophila homolog of human lissencephaly 1, reinforcing the role of the dynein complex in cell proliferation, dendritic morphogenesis and axonal transport. Phenotypic analysis of short stop/kakapo, which encodes a large cytoskeletal linker protein, reveals a novel function in regulating microtubule polarity in neurons. MB neurons mutant for flamingo, which encodes a seven transmembrane cadherin, extend processes beyond their wild-type dendritic territories. Overexpression of Flamingo results in axon retraction. Our results suggest that most genes involved in neuronal morphogenesis play multiple roles in different aspects of neural development, rather than performing a dedicated function limited to a specific process.

Giant axonal neuropathy (GAN), an autosomal recessive disorder caused by mutations in GAN, is characterized cytopathologically by cytoskeletal abnormality. Based on its sequence, gigaxonin contains an NH2-terminal BTB domain followed by six kelch repeats, which are believed to be important for protein–protein interactions (Adams, J., R. Kelso, and L. Cooley. 2000. Trends Cell Biol. 10:17–24.). Here, we report the identification of a neuronal binding partner of gigaxonin. Results obtained from yeast two-hybrid screening, cotransfections, and coimmunoprecipitations demonstrate that gigaxonin binds directly to microtubule-associated protein (MAP)1B light chain (LC; MAP1B-LC), a protein involved in maintaining the integrity of cytoskeletal structures and promoting neuronal stability. Studies using double immunofluorescent microscopy and ultrastructural analysis revealed physiological colocalization of gigaxonin with MAP1B in neurons. Furthermore, in transfected cells the specific interaction of gigaxonin with MAP1B is shown to enhance the microtubule stability required for axonal transport over long distance. At least two different mutations identified in GAN patients (Bomont, P., L. Cavalier, F. Blondeau, C. Ben Hamida, S. Belal, M. Tazir, E. Demir, H. Topaloglu, R. Korinthenberg, B. Tuysuz, et al. 2000. Nat. Genet. 26:370–374.) lead to loss of gigaxonin–MAP1B-LC interaction. The devastating axonal degeneration and neuronal death found in GAN patients point to the importance of gigaxonin for neuronal survival. Our findings may provide important insights into the pathogenesis of neurodegenerative disorders related to cytoskeletal abnormalities.

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STUDY DESIGN: A five-year retrospective review was undertaken of all computed tomographic pulmonary angiograms (CTPAs) performed on obstetric patients at Galway University Hospital, a tertiary level centre, delivering approximately three thousand babies a year, between 2011 and 2016. Formal reports of each CTPA were reviewed via the hospital's electronic database IMPAX. Data including age, presenting symptoms and signs, pre/post-natal status, and results were collected. The proportion of suboptimal images was noted as was the incidence of other relevant pathology detected by scan. Data was analysed and the positive and negative yields calculated. Statistical analysis was performed to determine whether the difference in numbers between antenatal and postnatal groups was significant. RESULTS: A total of 149 CTPA scans were performed. Eighty-four (56.4%) of these were on antenatal patients and sixty-five (43.6%) on postpartum patients. Only five (5.9%) of the CTPAs performed antenatally were positive whereas nine patients (13.8%) were positive in the postnatal group (p¼0.101) Total positive yield was 9.4% (14/ 149). For each positive result there were nine negative CTPAs performed. A total of 32 scans (21.47%) were reported as demonstrating suboptimal images. Subsegmental emboli could not be fully excluded in this group and further imaging was required in cases on on-going clinical suspicion. Twenty-four (16%) scans reported other relevant pathological findings. These commonly showed evidence of consolidation, effusions and atelectasis but other unusual findings were also picked up including liver lesions, lymphadenopathy, cavitary masses and a retrosternal thyroid nodule. Many unexpected findings required further follow-up imaging. CONCLUSION: CTPA exposes maternal breast tissue to a radiation dose that can increase women's lifetime risk of breast cancer. This study highlights the dilemma of clinical management in pregnant and postnatal women with chest symptoms. It also demonstrates the usefulness and limitations of using CTPA as an imaging modality it this cohort. OBJECTIVE:A growing body of evidence suggests that antepartum and postpartum VTE have distinct pathophysiological etiologies. The aim of this study was to identify and compare the risk factors for both time periods. STUDY DESIGN: A case-control study was performed; cases were defined as antepartum or postpartum VTE at Toledo Hospital (2010)(2011)(2012)(2013)(2014)(2015). VTE-free controls were frequency matched 1:3 by age and race. Data was extracted from paper-based records and EHR. A VTE was confirmed by objective imaging (duplex Doppler, CTA or V/Q scan). Patients with prior history of VTE or known coagulopathies were included in the study. Analysis was performed with SPSSv19. RESULTS:A total of 83 cases (antepartum n¼51, postpartum n¼32) and 243 controls were identified. From more than 40 candidate variables only few were significantly associated with VTE. Antepartum risk factors for VTE included: 1) personal history of VTE (OR 10.3, 95% CI 2.5-41.7...