ASPM and CITK regulate spindle orientation by affecting the dynamics of astral microtubules.

Correct orientation of cell division is considered an important factor for the achievement of normal brain size, as mutations in genes that affect this process are among the leading causes of microcephaly. Abnormal spindle orientation is associated with reduction of the neuronal progenitor symmetric divisions, premature cell cycle exit, and reduced neurogenesis. This mechanism has been involved in microcephaly resulting from mutation of ASPM, the most frequently affected gene in autosomal recessive human primary microcephaly (MCPH), but it is presently unknown how ASPM regulates spindle orientation. In this report, we show that ASPM may control spindle positioning by interacting with citron kinase (CITK), a protein whose loss is also responsible for severe microcephaly in mammals. We show that the absence of CITK leads to abnormal spindle orientation in mammals and insects. In mouse cortical development, this phenotype correlates with increased production of basal progenitors. ASPM is required to recruit CITK at the spindle, and CITK overexpression rescues ASPM phenotype. ASPM and CITK affect the organization of astral microtubules (MT), and low doses of MT-stabilizing drug revert the spindle orientation phenotype produced by their knockdown. Finally, CITK regulates both astral-MT nucleation and stability. Our results provide a functional link between two established microcephaly proteins.

Mutations of the catalytic subunit of RAB3GAP cause Warburg Micro syndrome.

Warburg Micro syndrome (WARBM1) is a severe autosomal recessive disorder characterized by developmental abnormalities of the eye and central nervous system and by microgenitalia. We identified homozygous inactivating mutations in RAB3GAP, encoding RAB3 GTPase activating protein, a key regulator of the Rab3 pathway implicated in exocytic release of neurotransmitters and hormones, in 12 families with Micro syndrome. We hypothesize that the underlying pathogenesis of Micro syndrome is a failure of exocytic release of ocular and neurodevelopmental trophic factors.

Regional changes in thalamic shape and volume with increasing age.

The thalamus undergoes significant volume loss and microstructural change with increasing age. Alterations in thalamo-cortical connectivity may contribute to the decline in cognitive ability associated with aging. The aim of this study was to assess changes in thalamic shape and in the volume and diffusivity of thalamic regions parcellated by their connectivity to specific cortical regions in order to test the hypothesis age related thalamic change primarily affects thalamic nuclei connecting to the frontal cortex. Using structural magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI), we assessed thalamic volume and diffusivity in 86 healthy volunteers, median (range) age 44 (20-74) years. Regional thalamic micro and macro structural changes were assessed by segmenting the thalamus based on connectivity to the frontal, parietal, temporal and occipital cortices and determining the volumes and mean diffusivity of the thalamic projections. Linear regression analysis was performed to test the relationship between increasing age and (i) normalised thalamic volume, (ii) whole thalamus diffusion measures, (iii) mean diffusivity (MD) of the thalamo-cortical projections, and (iv) volumes of the thalamo-cortical projections. We also assessed thalamic shape change using vertex analysis. We observed a significant reduction in the volume and a significant increase in MD of the whole thalamus with increasing age. The volume of the thalamo-frontal projections decreased significantly with increasing age, however there was no significant relationship between the volumes of the thalamo-cortical projections to the parietal, temporal, and occipital cortex and age. Thalamic shape analysis showed that the greatest shape change was in the anterior thalamus, incorporating regions containing the anterior nucleus, the ventroanterior nucleus and the dorsomedial nucleus. To explore these results further we studied two additional groups of subjects (a younger and an older aged group, n=20), which showed that the volume of the thalamo-frontal projections was correlated to executive functions scores, as assessed by the Stroop test. These data suggest that atrophy of the frontal thalamo-cortical unit may explain, at least in part, disorders of attention, working memory and executive function associated with increasing age.

Quizzing for success: Evaluation of the impact of feedback quizzes on the experiences and academic performance of undergraduate students in two clinical pharmacokinetics courses.

BACKGROUND AND PURPOSE: Students find clinical pharmacokinetics and pharmacodynamics courses challenging, partly due to their mathematical nature. This study aimed to retrospectively evaluate the impact of "feedback quizzes" on the experiences and academic performance of undergraduate pharmacy students at an Australian university. EDUCATIONAL ACTIVITY AND SETTING: Formative paper-based quizzes were introduced into tutorials in an intermediate third-year pharmacokinetics course, and summative online quizzes were introduced into a subsequent advanced fourth-year course that included a pharmacokinetics component. Experience data were drawn from institutional student evaluation surveys, and academic performance was obtained from exam results. Student experiences and academic performance were compared pre- and post-intervention using the Test of Equal Proportions and Mann-Whitney-Wilcoxon, respectively. FINDINGS: A greater proportion of students in both quiz cohorts were satisfied with the overall course experience compared to the pre-curricular change cohort (intermediate: 87% vs. 78%; advanced: 63% vs. 50%). Students who received quizzes in both years performed better in the clinical pharmacokinetics component of the advanced course compared to a prior cohort who had no quizzes (85.7% vs. 77.8%). SUMMARY: Feedback quizzes, whether formative or summative, administered in-class or outside class, can enhance learning and performance and lead to improvements in student satisfaction with clinical pharmacokinetics courses. Scaffolding of feedback quizzes across year levels can provide students with added confidence when attempting assessment. Collaboration between research-focused and teaching-focused staff can lead to increased scholarship of teaching and learning activities.

His-Purkinje lineages and development.

The heartbeat is initiated and coordinated by a multi-component set of specialized muscle tissues collectively referred to as the pacemaking and conduction system. Over the last few years, impetus has gathered into unravelling the cellular and molecular processes that regulate differentiation and integration of this essential cardiac network. One focus of our collective work has been the developmental history of cells comprising His-Purkinje tissues of the conduction system. This interest in part arose from studies of the expression of connexins in periarterial Purkinje fibres of the chick heart. Using lineage-tracing strategies, including those based on replication-defective retroviruses and adenoviruses, it has been shown that conduction cells are derived from multipotent, cardiomyogenic progenitors in the tubular heart. Moreover, heterogeneity within myocardial clones has indicated that the elaboration of the conduction system in the chick embryo occurs by progressive, localized recruitment from within this pool of cardiomyogenic cells. Cell birth dating has revealed that inductive conscription of cells to central elements of the conduction system (e.g. the His bundle) precedes recruitment to the peripheral components of the network (i.e. subendocardial and periarterial Purkinje fibres). Birth dating studies in rodents suggest an analogous recruitment process is occurring in this species. In addition to summarizing earlier work, this chapter provides information on ongoing studies of cell-cell signalling and transcriptional mechanisms that may regulate the development of His-Purkinje tissues.

Wnt11 and Wnt7a are up-regulated in association with differentiation of cardiac conduction cells in vitro and in vivo.

The heart beat is coordinated by a precisely timed sequence of action potentials propagated through cells of the conduction system. Previously, we have shown that conduction cells in the chick embryo are derived from multipotent, cardiomyogenic progenitors present in the looped, tubular heart. Moreover, analyses of heterogeneity within myocyte clones and cell birth dating have indicated that elaboration of the conduction system occurs by ongoing, localized recruitment from within this multipotent pool. In this study, we have focused on a potential role for Wnt signaling in development of the cardiac conduction system. Treatment of embryonic myocytes from chick with endothelin-1 (ET-1) has been shown to promote expression of markers of Purkinje fiber cells. By using this in vitro model, we find that Wnt11 are Wnt7a are up-regulated in association with ET-1 treatment. Moreover, in situ hybridization reveals expression, although not temporal coincidence of, Wnt11 and Wnt7a in specialized tissues in the developing heart in vivo. Specifically, whereas Wnt11 shows transient and prominent expression in central elements of the developing conduction system (e.g., the His bundle), relative increases in Wnt7a expression emerge at sites consistent with the location of peripheral conduction cells (e.g., subendocardial Purkinje fibers). The patterns of Wnt11 and Wnt7a expression observed in vitro and in the embryonic chick heart appear to be consistent with roles for these two Wnts in differentiation of cardiac conduction tissues.