The tumor suppressor gene, lethal(2)giant larvae (1(2)g1), is required for cell shape change of epithelial cells during Drosophila development

Cooperative regulation of cell polarity and growth by Drosophila tumor suppressors

Loss of cell polarity and tissue architecture are characteristics of malignant cancers derived from epithelial tissues. We provide evidence from Drosophila that a group of membrane-associated proteins act in concert to regulate both epithelial structure and cell proliferation. Scribble (Scrib) is a cell junction-localized protein required for polarization of embryonic and, as demonstrated here, imaginal disc and follicular epithelia. We show that the tumor suppressors lethal giant larvae (lgl) and discs-large (dlg) have identical effects on all three epithelia, and that scrib also acts as a tumor suppressor. Scrib and Dlg colocalize and overlap with Lgl in epithelia; activity of all three genes is required for cortical localization of Lgl and junctional localization of Scrib and Dlg. scrib, dlg, and lgl show strong genetic interactions. Our data indicate that the three tumor suppressors act together in a common pathway to regulate cell polarity and growth control.

Genetic control of epithelial cell polarity: lessons from Drosophila

The cell biology of polarized epithelial cells is a field of major interest to cell and developmental biologists. In addition to the study of epithelial cells in tissue culture, genetically tractable systems have been employed to examine the functional importance of individual molecules. Here I review recent progress that has been made using Drosophila as a model system to study apical-basal epithelial cell polarity. In this system, a large number of genes have been identified that are essential for the development and maintenance of the apical-basal polarity of epithelial cells in different developmental contexts. In this article, the recent progress in three models, i.e., establishment of the ectoderm and midgut epithelia during embryogenesis, epithelial polarity of imaginal discs, and epithelial development of the follicle cells during oogenesis will be discussed.

Systematic variation in gene expression patterns in human cancer cell lines

We used cDNA microarrays to explore the variation in expression of approximately 8,000 unique genes among the 60 cell lines used in the National Cancer Institute's screen for anti-cancer drugs. Classification of the cell lines based solely on the observed patterns of gene expression revealed a correspondence to the ostensible origins of the tumours from which the cell lines were derived. The consistent relationship between the gene expression patterns and the tissue of origin allowed us to recognize outliers whose previous classification appeared incorrect. Specific features of the gene expression patterns appeared to be related to physiological properties of the cell lines, such as their doubling time in culture, drug metabolism or the interferon response. Comparison of gene expression patterns in the cell lines to those observed in normal breast tissue or in breast tumour specimens revealed features of the expression patterns in the tumours that had recognizable counterparts in specific cell lines, reflecting the tumour, stromal and inflammatory components of the tumour tissue. These results provided a novel molecular characterization of this important group of human cell lines and their relationships to tumours in vivo.

The first oncogene in Drosophila melanogaster

Discovered by Bridges in the 1930s, lethal (2) giant larvae was the first of more than 27 recessive oncogenes identified in Drosophila, which provides an excellent model to study neoplastic mechanisms due to the fact that homologs of human oncogenes and tumor suppressors have been isolated and most of the complexes and associated pathways are conserved. This review explores the potential of neoplastic studies in Drosophila to help understand the genomic mechanisms of neoplastic development in vertebrates and invertebrates. Starting from neoplasms and genetic mutations, the article introduces the reader to one of the possibilities that the studies on neoplastic mechanisms of oncogenes in Drosophila can provide a great understanding of the developmental progression in both vertebrates and invertebrates.

Molecular mechanisms of nonmuscle myosin-II regulation

Myosin II, the conventional two-headed myosin that forms bipolar filaments, is directly involved in regulating cytokinesis, cell motility and cell morphology in nonmuscle cells. To understand the mechanisms by which nonmuscle myosin-II regulates these processes, investigators are now looking at the regulation of this molecule in vertebrate nonmuscle cells. The identification of multiple isoforms of nonmuscle myosin-II, whose activities and regulation differ from that of smooth muscle myosin-II, suggests that, in addition to regulatory light chain phosphorylation, other regulatory mechanisms control vertebrate nonmuscle myosin-II activity.

[Dorsal closure in Drosophila. A genetic model for wound healing?]

Dorsal closure (DC) is a morphogenetic movement that establishes the dorsal ectoderm of the drosophila embryo. During this process, the two lateral epithelia stretch toward the dorsal midline, the suture line of the two leading edges. Cell migration during DC relies both on cell shape change controlled by the activity of the JNK pathway in the leading edge cells and modification of cell adhesiveness, probably dependent upon activation of the Dpp (TGF-beta) pathway. Coupling of the JNK and TGF-beta pathways is essential. The sequence of the cellular and molecular events of DC highlights interesting common features with wound healing in vertebrates. Like DC, wound healing relies on the migration of epithelia bordered by leading edges controlling the direction and speed of the movement. This review summarizes recent data concerning the control of epithelial morphogenesis during DC and the bases of wound healing. The molecular and cellular events that underlie these two analogous migratory processes are detailed, discussed and compared. We suggest that DC is a good genetic model for wound healing studying.

The products of ribbon and raw are necessary for proper cell shape and cellular localization of nonmuscle myosin in Drosophila

Mutations in the genes rib and raw cause defects in the morphology of a number of tissues in homozygous mutant embryos. A variety of tubular epithelial tissues adopt a wide, round shape in mutants and dorsal closure fails. Cells of the normal tubular epithelia are columnar and wedge-shaped, and cells of the epidermis become elongated dorsoventrally as dorsal closure occurs. However, the cells of mutants are round or cuboidal in all of the tissues with mutant phenotypes, consistent with the hypothesis that the products of these genes are required for proper cell shape. Cytoskeletal defects, in particular, defects in myosin-driven contraction of the cortical actin cytoskeleton, could be responsible for the lack of specific cell shapes in mutant embryos. This possibility is supported by our observation that the intracellular localization of nonmuscle myosin to the leading edge of the dorsally closing epidermis is absent or reduced in rib and raw mutant embryos. In contrast, the band of actin that is also located at the leading edge is neither eliminated nor interrupted by either rib or raw mutations. Furthermore, mutations of zipper, the gene encoding the nonmuscle myosin heavy chain, exhibit mutant phenotypes in most of the same tissues affected by rib and raw, and many of the phenotypes are similar to those of rib and raw. Therefore, the products of rib and raw may be required for proper myosin-driven contraction of the actin cytoskeleton.

Cellular control lies in the balance of forces

Mechanical tension generated within the cytoskeleton of living cells is emerging as a critical regulator of biological function in diverse situations ranging from the control of chromosome movement to the morphogenesis of the vertebrate brain. In this article, we review recent advances that have been made in terms of understanding how cells generate, transmit and sense mechanical tension, as well as how they use these forces to control their shape and behavior. An integrated view of cell regulation that incorporates mechanics and structure as well as chemistry is beginning to emerge.

Regulation of cell differentiation by the Drosophila Jun kinase cascade

Recent studies have defined a new Drosophila Jun amino-terminal kinase (DJNK) pathway. The first role that has been uncovered for this pathway is the control of cell differentiation and morphogenesis during the process of dorsal closure. This phosphorylation cascade has been conserved during evolution and several reports suggest that it becomes activated in response to the action of small GTPases. DJNK signalling impinges on transcription factors as DJun and Anterior open and eventually controls the expression of target genes such as decapentaplegic and puckered. Important progress has been made in the study of the coordination of DJNK and Decapentaplegic signalling during dorsal closure and their role in the control of cell shape changes--and possibly cell polarity--by promoting cytoskeletal changes.