Collectively, our data reveal that the cell polarity regulators Lgl, aPKC, and Crumbs regulate the SWH pathway by two distinct pathways: Lgl acts antagonistically to aPKC to regulate Hippo and RASSF localization, whereas Crumbs regulates Expanded localization. Thus, our study implicates Lgl, aPKC, and Crumbs as regulators of tissue growth via the SWH pathway.

A key goal of developmental biology is to understand the mechanisms that coordinate organ growth. It has long been recognized that the genes that control apico-basal cell polarity also regulate tissue growth. How loss of cell polarity contributes to tissue overgrowth has been the subject of much speculation. Do loss-of-function mutations in cell polarity regulators result in secondary effects that globally deregulate cell proliferation, or do these genes specifically control growth pathways? Three recent papers have shown that the apico-basal polarity determinants Lgl/aPKC and Crb regulate tissue growth independently of their roles in cell polarity and coordinately regulate cell proliferation and cell death via the Salvador/Warts/Hippo (SWH) pathway. Lgl/aPKC are required for the correct localization of Hippo (Hpo)/Ras associated factor (RASSF), while Crb regulates the levels and localization of Expanded (Ex), indicating that cell polarity determinants modify SWH pathway activity by distinct mechanisms. Here, we review the key data that support these conclusions, highlight remaining questions and speculate on the underlying mechanisms by which the cell polarity complexes interact with the SWH pathway. Understanding the interactions between cell polarity regulators and the SWH pathway will improve our knowledge of how epithelial organization and tissue growth are coordinated during development and perturbed in disease states such as cancer.

late onset of kidney tubule defects with abnormal cellular morphology. We have generated a Tg(phd3:GFP)/+; vhl1/+ transgenic line, which exhibit robust GFP expression in the vhl1/vhl1 background, essentially acting as an in vivo fluorescent reporter to identify the mutant cells/embryos. To induce VHL kidney tumors in fish, we have utilized this transgenic line to generate donor embryos and transplanted the mutant blastomeres to the wild type host embryos, specifically targeting these mutant cells to the renal primordium. We report that Tg(phd3:GFP) line is a live reporter for monitoring hypoxia and the induction of HIF signaling. We shall present our observations on the fate of the vhl1 mutant cells in the chimeric fish and also our analysis for the possible occurrence of neoplasia in these chimeric fish.Insufficient maternal nutrition can lead to intra-uterine growth restriction and a small-for-gestational-age fetus. Nevertheless, growth of the CNS is reduced much less dramatically than that of the rest of the body. Fetal brain sparing, which occurs at the expense of organs such as the liver, is associated in humans with adult-onset metabolic diseases, as first hypothesised by Barker in the 1980s and 1990s. Although the underlying molecular mechanisms are far from clear, brain sparing appears be a common feature of many animal species, including those that develop ex-utero.In Drosophila, we observe that dietary restriction during the late-postembryonic growth phase results in a near-normal sized CNS contained within a tiny larva. For most larval cell types, growth and division are entirely dependent upon extrinsic signals that are high under fed conditions, such as insulin and amino acids. Surprisingly, we find that neural stem-cell like progenitors (neuroblasts) are highly atypical in that they divide normally in the absence of TOR (a kinase transducing amino-acid signals) or a functional Insulin Receptor. Instead, clonal analysis indicates that neuroblast divisions are dependent upon an alternative kinase pathway that is constitutively active under both fed and starved conditions. These results identify a molecular mechanism for brain sparing and illustrate how some developing organs compete more effectively than others for limited nutritional resources. The Drosophila neoplastic tumor suppressor, Lethal-2-giantlarvae (Lgl), functions in the establishment of apico-basal cell polarity and in negatively regulating cell proliferation, however how this is achieved is little understood. Homozygous lgl À larvae show loss of apico-basal polarity in epithelial tissues. We therefore used clonal analysis (FLP/FRT) in the developing 3rd instar and pupal eye, allowing us to investigate the effects of lgl mutations in the context of surrounding wild-type tissue at various stages of development. Induction of lgl mutant clones in eye imaginal discs leads to ectopic proliferation. Further analysis shows that lgl mutants genetically interact with components of the Salvador/Warts/ Hippo (SWH) tumor suppressor pathway. Downregul...

The junctional neoplastic tumour suppressors, Lgl, Dlg and Scrib, function in apical-basal cell polarity and limiting cell proliferation. In homozygous lgl, dlg or scrib mutants over-proliferation and polarity loss occurs in the larval imaginal disc epithelium.However, in lgl mutant mosaic eye epithelium, ectopic Cyclin E expression and cell proliferation occurs without loss of polarity. lgl mutant clones also show upregulation of the inhibitor of apoptosis, DIAP1, and developmental cell death is prevented. These effects on cell proliferation and survival can be explained by the misregulation of several signalling pathways in lgl mutant tissue.However, despite these effects on lgl mutant clonal growth, the overgrowth of the mutant tissue is restrained by differentiation and JNK-mediated apoptosis at the clonal borders.Cancer requires cooperation between tumour suppressors and oncogenes, leading to continued cell proliferation, increased survival, decreased differentiation and increased invasion. Oncogenic alleles of Ras (Ras V12 ) or Notch (Notch intra ) cooperate with mutants in scrib, dlg or lgl to produce invasive tumours. In a genetic screen for novel genes that when overexpressed cooperate with scrib mutants similarly to oncogenic Ras or Notch, we identified abrupt, which encodes a BTB/POZ zinc finger domain transcription factor.We are investigating the mechanism by which this novel oncogene cooperates with scrib mutants to promote tumourigenesis. Melanoma is the most aggressive and lethal form of skin cancer. In melanoma, melanocytes undergo aberrant proliferation, and invade other tissues giving rise to local and distant metastases. Using the GAL4-UAS system, we have developed a zebrafish transgenic line that expresses oncogenic Ras under the kit-a promoter and develops melanomas by 1-3 months of age. Local infiltrations of adjacent tissues (gills, muscles, brain) are present in most cases, whereas distant metastases are mediated by intravasation into newly formed tumor vessels. Transgenic larvae show already at 3 dpf an over-pigmentation phenotype, due to an increased number and size of melanophores, coupled to abnormal migration. We have therefore used the transgenic larvae to screen for pathways and/or mechanisms that revert the abnormal growth and migration phenotype of transformed melanophores. By expressing a dominant negative form of rab5 in melanophores through the UAS system, we observed profound modification of the polarity, size and migration of transformed melanocytes, thus indicating that endocytosis and/or vesicle trafficking is necessary for the transforming activity of oncogenic Ras in these cells. We hypothesized that Ras may rely on endocytosis or vesicular traffic to activate Rac, one of the Ras effectors mediating both transformation and abnormal migration of melanophores. Further studies are in progress to elucidate the role of endocytic processes and the cargos of rab5+ vesicles in Ras induced melanoma. Thus our model offers the advantage of both larval and adult phenotypes and allows...