α-Spectrin and integrins act together to regulate actomyosin and columnarization, and to maintain a monolayered follicular epithelium.

The spectrin cytoskeleton crosslinks actin to the membrane, and although it has been greatly studied in erythrocytes, much is unknown about its function in epithelia. We have studied the role of spectrins during epithelia morphogenesis using the Drosophila follicular epithelium (FE). As previously described, we show that α-Spectrin and ß-Spectrin are essential to maintain a monolayered FE, but, contrary to previous work, spectrins are not required to control proliferation. Furthermore, spectrin mutant cells show differentiation and polarity defects only in the ectopic layers of stratified epithelia, similar to integrin mutants. Our results identify α-Spectrin and integrins as novel regulators of apical constriction-independent cell elongation, as α-Spectrin and integrin mutant cells fail to columnarize. Finally, we show that increasing and reducing the activity of the Rho1-Myosin II pathway enhances and decreases multilayering of α-Spectrin cells, respectively. Similarly, higher Myosin II activity enhances the integrin multilayering phenotype. This work identifies a primary role for α-Spectrin in controlling cell shape, perhaps by modulating actomyosin. In summary, we suggest that a functional spectrin-integrin complex is essential to balance adequate forces, in order to maintain a monolayered epithelium.

Large-scale functional annotation and expanded implementations of the P{wHy} hybrid transposon in the Drosophila melanogaster genome.

Whole genome sequencing of the model organisms has created increased demand for efficient tools to facilitate the genome annotation efforts. Accordingly, we report the further implementations and analyses stemming from our publicly available P{wHy} library for Drosophila melanogaster. A two-step regime-large scale transposon mutagenesis followed by hobo-induced nested deletions-allows mutation saturation and provides significant enhancements to existing genomic coverage. We previously showed that, for a given starting insert, deletion saturation is readily obtained over a 60-kb interval; here, we perform a breakdown analysis of efficiency to identify rate-limiting steps in the process. Transrecombination, the hobo-induced recombination between two P{wHy} half molecules, was shown to further expand the P{wHy} mutational range, pointing to a potent, iterative process of transrecombination-reconstitution-transrecombination for alternating between very large and very fine-grained deletions in a self-contained manner. A number of strains also showed partial or complete repression of P{wHy} markers, depending on chromosome location, whereby asymmetric marker silencing allowed continuous phenotypic detection, indicating that P{wHy}-based saturational mutagenesis should be useful for the study of heterochromatin/positional effects.

The salvador-warts-hippo pathway is required for epithelial proliferation and axis specification in Drosophila.

In Drosophila, the body axes are specified during oogenesis through interactions between the germline and the overlying somatic follicle cells [1-5]. A Gurken/TGF-alpha signal from the oocyte to the adjacent follicle cells assigns them a posterior identity [6, 7]. These posterior cells then signal back to the oocyte, thereby inducing the repolarization of the microtubule cytoskeleton, the migration of the oocyte nucleus, and the localization of the axis specifying mRNAs [8-10]. However, little is known about the signaling pathways within or from the follicle cells responsible for these patterning events. We show that the Salvador Warts Hippo (SWH) tumor-suppressor pathway is required in the follicle cells in order to induce their Gurken- and Notch-dependent differentiation and to limit their proliferation. The SWH pathway is also required in the follicle cells to induce axis specification in the oocyte, by inducing the migration of the oocyte nucleus, the reorganization of the cytoskeleton, and the localization of the mRNAs that specify the anterior-posterior and dorsal-ventral axes of the embryo. This work highlights a novel connection between cell proliferation, cell growth, and axis specification in egg chambers.

MicroRNA functions in animal development and human disease.

Five years into the 'small RNA revolution' it is hard not to share in the excitement about the rapidly unravelling biology of microRNAs. Since the discovery of the first microRNA gene, lin-4, in the nematode Caenorhabditis elegans, many more of these short regulatory RNA genes have been identified in flowering plants, worms, flies, fish, frogs and mammals. Currently, about 2% of the known human genes encode microRNAs. MicroRNAs are essential for development and this review will summarise our current knowledge of animal microRNA function. We will also discuss the emerging links of microRNA biology to stem cell research and human disease, in particular cancer.