Faculty Bibliography

We investigated the control of proliferation and differentiation in the larval Caenorhabditis elegans hermaphrodite germ line through analysis of glp-1 and lag-2 mutants, cell ablations, and ultrastructural data. After the first several rounds of germ cell division, GLP-1, a receptor of the LIN-12/Notch family, governs germline proliferation. We analyzed the proximal proliferation (Pro) phenotype in glp-1(ar202) and found that initial meiosis was delayed and spatially mispositioned. This is due, at least in part, to a heightened response of the mutant GLP-1 receptor to multiple sources of the somatic ligand LAG-2, including the proximal somatic gonad. We investigated whether proximal LAG-2 affects germline proliferation in the wild type. Our results indicate that (1) LAG-2 is necessary for GLP-1-mediated germline proliferation and prevention of early meiosis, and (2) several distinct anatomical sources of LAG-2 in the larval somatic gonad functionally overlap to promote proliferation and prevent early meiosis. Ultrastructural studies suggest that mitosis is not restricted to areas of direct DTC-germ line contact and that the germ line shares a common cytoplasm in larval stages. We propose that downregulation of the GLP-1 signaling pathway in the proximal germ line at the time of meiotic onset is under tight temporal and spatial control

Cancer cells are able to proliferate at accelerated rates within the confines of a three-dimensional (3D) extracellular matrix (ECM) that is rich in type I collagen. The mechanisms used by tumor cells to circumvent endogenous antigrowth signals have yet to be clearly defined. We find that the matrix metalloproteinase, MT1-MMP, confers tumor cells with a distinct 3D growth advantage in vitro and in vivo. The replicative advantage conferred by MT1-MMP requires pericellular proteolysis of the ECM, as proliferation is fully suppressed when tumor cells are suspended in 3D gels of protease-resistant collagen. In the absence of proteolysis, tumor cells embedded in physiologically relevant ECM matrices are trapped in a compact, spherical configuration and unable to undergo changes in cell shape or cytoskeletal reorganization required for 3D growth. These observations identify MT1-MMP as a tumor-derived growth factor that regulates proliferation by controlling cell geometry within the confines of the 3D ECM

During the ribosomal translocation, the binding of elongation factor G (EF-G) to the pretranslocational ribosome leads to a ratchet-like rotation of the 30S subunit relative to the 50S subunit in the direction of the mRNA movement. By means of cryo-electron microscopy we observe that this rotation is accompanied by a 20 A movement of the L1 stalk of the 50S subunit, implying that this region is involved in the translocation of deacylated tRNAs from the P to the E site. These ribosomal motions can occur only when the P-site tRNA is deacylated. Prior to peptidyl-transfer to the A-site tRNA or peptide removal, the presence of the charged P-site tRNA locks the ribosome and prohibits both of these motions

Trafficking of trophic factors in axons can occur in a retrograde and anterograde direction. Recent findings bring further support for a vesicle-based process for retrograde transport but raise new questions that need to be pursued. Unraveling the exact mechanisms that account for retrograde transport of neurotrophins and their receptors will reveal the cellular requirements for propagating trophic signals over long distances