The Fat Cadherin Acts through the Hippo Tumor-Suppressor Pathway to Regulate Tissue Size

Background: The Hippo tumor-suppressor pathway has emerged as a key signaling pathway that controls tissue size in Drosophila. Merlin, the Drosophila homolog of the human Neurofibromatosis type-2 (NF2) tumor-suppressor gene, and the related protein Expanded are the most upstream components of the Hippo pathway identified so far. However, components acting upstream of Expanded and Merlin, such as transmembrane receptors, have not yet been identified. Results: Here, we report that the protocadherin Fat acts as an upstream component in the Hippo pathway. Fat is a known tumor-suppressor gene in Drosophila, and fat mutants have severely overgrown imaginal discs. We found that the overgrowth phenotypes of fatmutants are similar to those of mutants in Hippo pathway components: fat mutant cells continued to proliferate after wild-type cells stopped proliferating, and fat mutant cells deregulated Hippo target genes such as cyclin E and diap1. Fat acts genetically and biochemically upstream of other Hippo pathway components such as Expanded, the Hippo and Warts kinases, and the transcriptional coactivator Yorkie. Fat is required for the stability of Expanded and its localization to the plasma membrane. In contrast, Fat is not required for Merlin localization, and Fat and Merlin act in parallel in growth regulation. Conclusions: Taken together, our data identify a cell-surface molecule that may act as a receptor of the Hippo signaling pathway

Trainee Career Outcomes Tracking: Postdoctoral Fellows at MD Anderson as a Case Study

https://openworks.mdanderson.org/ret/1000/thumbnail.jp

Transcription Factor FoxO1 Is Essential for Enamel Biomineralization

The Transforming growth factor β (Tgf-β) pathway, by signaling via the activation of Smad transcription factors, induces the expression of many diverse downstream target genes thereby regulating a vast array of cellular events essential for proper development and homeostasis. In order for a specific cell type to properly interpret the Tgf-β signal and elicit a specific cellular response, cell-specific transcriptional co-factors often cooperate with the Smads to activate a discrete set of genes in the appropriate temporal and spatial manner. Here, via a conditional knockout approach, we show that mice mutant for Forkhead Box O transcription factor FoxO1 exhibit an enamel hypomaturation defect which phenocopies that of the Smad3 mutant mice. Furthermore, we determined that both the FoxO1 and Smad3 mutant teeth exhibit changes in the expression of similar cohort of genes encoding enamel matrix proteins required for proper enamel development. These data raise the possibility that FoxO1 and Smad3 act in concert to regulate a common repertoire of genes necessary for complete enamel maturation. This study is the first to define an essential role for the FoxO family of transcription factors in tooth development and provides a new molecular entry point which will allow researchers to delineate novel genetic pathways regulating the process of biomineralization which may also have significance for studies of human tooth diseases such as amelogenesis imperfecta

Anthropometric indices of Gambian children after one or three annual rounds of mass drug administration with azithromycin for trachoma control.

BACKGROUND: Mass drug administration (MDA) with azithromycin, carried out for the control of blinding trachoma, has been linked to reduced mortality in children. While the mechanism behind this reduction is unclear, it may be due, in part, to improved nutritional status via a potential reduction in the community burden of infectious disease. To determine whether MDA with azithromycin improves anthropometric indices at the community level, we measured the heights and weights of children aged 1 to 4 years in communities where one (single MDA arm) or three annual rounds (annual MDA arm) of azithromycin had been distributed. METHODS: Data collection took place three years after treatment in the single MDA arm and one year after the final round of treatment in the annual MDA arm. Mean height-for-age, weight-for-age and weight-for-height z scores were compared between treatment arms. RESULTS: No significant differences in mean height-for-age, weight-for-age or weight-for-height z scores were found between the annual MDA and single MDA arms, nor was there a significant reduction in prevalence of stunting, wasting or underweight between arms. CONCLUSIONS: Our data do not provide evidence that community MDA with azithromycin improved anthropometric outcomes of children in The Gambia. This may suggest reductions in mortality associated with azithromycin MDA are due to a mechanism other than improved nutritional status

Hippo promotes proliferation arrest and apoptosis in the Salvador/Warts pathway

Proliferation and apoptosis must be precisely regulated to form organs with appropriate cell numbers and to avoid tumour growth. Here we show that Hippo (Hpo), the Drosophila homologue of the mammalian Ste20-like kinases, MST1/2, promotes proper termination of cell proliferation and stimulates apoptosis during development. hpo mutant tissues are larger than normal because mutant cells continue to proliferate beyond normal tissue size and are resistant to apoptotic stimuli that usually eliminate extra cells. Hpo negatively regulates expression of Cyclin E to restrict cell proliferation, downregulates the Drosophila inhibitor of apoptosis protein DIAP1, and induces the proapoptotic gene head involution defective (hid) to promote apoptosis. The mutant phenotypes of hpo are similar to those of warts (wts), which encodes a serine/threonine kinase of the myotonic dystrophy protein kinase family, and salvador (sav), which encodes a WW domain protein that binds to Wts. We find that Sav binds to a regulatory domain of Hpo that is essential for its function, indicating that Hpo acts together with Sav and Wts in a signalling module that coordinately regulates cell proliferation and apoptosis.status: publishe

Quantitative imaging of cell dynamics in mouse embryos using light-sheet microscopy

Single/selective-plane illumination, or light-sheet, systems offer several advantages over other fluorescence microscopy methods for live, 3D microscopy. These systems are valuable for studying embryonic development in several animal systems, such as Drosophila, C. elegans and zebrafish. The geometry of the light path in this form of microscopy requires the sample to be accessible from multiple sides and fixed in place so that it can be rotated around a single axis. Popular methods for mounting include hanging the specimen from a pin or embedding it in 1-2% agarose. These methods can be particularly problematic for certain samples, such as post-implantation mouse embryos, that expand significantly in size and are very delicate and sensitive to mounting. To overcome the current limitations and to establish a robust strategy for long-term (24 h) time-lapse imaging of E6.5-8.5 mouse embryos with light-sheet microscopy, we developed and tested a method using hollow agarose cylinders designed to accommodate for embryonic growth, yet provide boundaries to minimize tissue drift and enable imaging in multiple orientations. Here, we report the first 24-h time-lapse sequences of post-implantation mouse embryo development with light-sheet microscopy. We demonstrate that light-sheet imaging can provide both quantitative data for tracking changes in morphogenesis and reveal new insights into mouse embryogenesis. Although we have used this approach for imaging mouse embryos, it can be extended to imaging other types of embryos as well as tissue explants

Cardiovascular Patterning as Determined by Hemodynamic Forces and Blood Vessel Genetics

<div><p>Background</p><p>Vascular patterning depends on coordinated timing of arteriovenous specification of endothelial cells and the concomitant hemodynamic forces supplied by the onset of cardiac function. Using a combination of 3D imaging by OPT and embryo registration techniques, we sought to identify structural differences between three different mouse models of cardiovascular perturbation.</p><p>Results</p><p><i>Endoglin</i> mutant mice shared a high degree of similarity to <i>Mlc2a</i> mutant mice, which have been shown to have a primary developmental heart defect causing secondary vessel remodeling failures. <i>Dll4</i> mutant mice, which have well-characterized arterial blood vessel specification defects, showed distinct differences in vascular patterning when compared to the disruptions seen in <i>Mlc2a</i>^-/- and <i>Eng</i>^-/- models. While <i>Mlc2a</i>^-/- and <i>Eng</i>^-/- embryos exhibited significantly larger atria than wild-type, <i>Dll4</i>^-/- embryos had significantly smaller hearts than wild-type, but this quantitative volume decrease was not limited to the developing atrium. <i>Dll4</i>^-/- embryos also had atretic dorsal aortae and smaller trunks, suggesting that the cardiac abnormalities were secondary to primary arterial blood vessel specification defects.</p><p>Conclusions</p><p>The similarities in <i>Eng</i>^-/- and <i>Mlc2a</i>^-/- embryos suggest that <i>Eng</i>^-/- mice may suffer from a primary heart developmental defect and secondary defects in vessel patterning, while defects in <i>Dll4</i>^-/- embryos are consistent with primary defects in vessel patterning.</p></div

Registration of mutant mice across all three mouse lines reveals that <i>Dll4</i> have significantly different signal intensity maps compared to <i>Mlc2a</i> and <i>Eng</i> mice.

<p><i>Dll4</i>^-/- mice were compared to the pooled population of <i>Mlc2a</i>^-/- and <i>Eng</i>^-/- mice at all time points after registration. (A-C) are sagittal slices through an individual <i>Eng</i>-/-, <i>Mlc2a</i>^-/-, and <i>Dll4</i>^-/- mouse, respectively. The red cross-hair corresponds to the common ventricle in both the <i>Eng</i>^-/- (A) and <i>Mlc2a</i>^-/- (B) mouse, but not in the <i>Dll4</i>^-/- mouse (C) because its heart tube is still linear. (D) illustrates this statistically: the average autofluorescence map has been overlaid with the signal intensity map, and the <i>Dll4</i>^-/- mice display a lack of signal intensity (blue shading) in the area where the common ventricle should be forming. Slices through the vascular scan of each embryo confirms this finding (A′—D′). The red cross-hair is placed in the centre of the antrioventricular canal of the <i>Eng</i>^-/- mouse (A′), the <i>Mlc2a</i>^-/- mouse (B′), but not in the <i>Dll4</i>^-/- mouse (C′). Statistically, this is illustrated when the average vascular scan is overlaid with the signal intensity map (D′): the <i>Dll4</i>^-/- mice display a lack of signal (blue shading) in the outer ventricle area of the heart compared to the pooled <i>Eng</i>^-/- and <i>Mlc2a</i>^-/- embryos. The colour bar presents the t-statistic of which the minimum corresponds to a FDR threshold of 10%. Scale bar = 500μm.</p

Registration of mutant mice across all three mouse lines reveals that <i>Dll4</i> have significantly different Jacobian determinant maps compared to <i>Mlc2a</i> and <i>Eng</i> mice.

<p><i>Dll4</i>^-/- mice were compared to the pooled population of <i>Mlc2a</i>^-/- and <i>Eng</i>^-/- mice at all time points after registration. (A-C) are sagittal slices through the average 17–20 somite autofluorescence image of all the mutants in the pipeline overlaid with the Jacobian determinant heat map generated during the registration, and in each slice it is evident that the <i>Dll4</i> mice are smaller than the other mutants in both the trunk and heart regions (blue shading). This is also qualitatively obvious when isosurface images of representative <i>Eng</i>^-/- (D), <i>Mlc2a</i>^-/- (E), and <i>Dll4</i>^-/- mice are shown side-by-side. The <i>Dll4</i>^-/- mouse also has a significantly growth-delayed, linear heart tube (compare heart tube geometry between D-F). The colour bar presents the t-statistic of which the minimum corresponds to a FDR threshold of 10%. Scale bar = 500μm.</p

The fat cadherin acts through the hippo tumor-suppressor pathway to regulate tissue size

The Hippo tumor-suppressor pathway has emerged as a key signaling pathway that controls tissue size in Drosophila. Merlin, the Drosophila homolog of the human Neurofibromatosis type-2 (NF2) tumor-suppressor gene, and the related protein Expanded are the most upstream components of the Hippo pathway identified so far. However, components acting upstream of Expanded and Merlin, such as transmembrane receptors, have not yet been identified.status: publishe