Genetic interactions among ADAMTS metalloproteases and basement membrane molecules in cell migration in Caenorhabditis elegans

During development of the Caenorhabditis elegans gonad, the gonadal leader cells, called distal tip cells (DTCs), migrate in a U-shaped pattern to form the U-shaped gonad arms. The ADAMTS (a disintegrin and metalloprotease with thrombospondin motifs) family metalloproteases MIG-17 and GON-1 are required for correct DTC migration. Mutations in mig-17 result in misshapen gonads due to the misdirected DTC migration, and mutations in gon-1 result in shortened and swollen gonads due to the premature termination of DTC migration. Although the phenotypes shown by mig-17 and gon-1 mutants are very different from one another, mutations that result in amino acid substitutions in the same basement membrane protein genes, emb-9/collagen IV a1, let-2/collagen IV a2 and fbl-1/fibulin-1, were identified as genetic suppressors of mig-17 and gon-1 mutants. To understand the roles shared by these two proteases, we examined the effects of the mig-17 suppressors on gon-1 and the effects of the gon-1 suppressors and enhancers on mig-17 gonadal defects. Some of the emb-9, let-2 and fbl-1 mutations suppressed both mig-17 and gon-1, whereas others acted only on mig-17 or gon-1. These results suggest that mig-17 and gon-1 have their specific functions as well as functions commonly shared between them for gonad formation. The levels of collagen IV accumulation in the DTC basement membrane were significantly higher in the gon-1 mutants as compared with wild type and were reduced to the wild-type levels when combined with suppressor mutations, but not with enhancer mutations, suggesting that the ability to reduce collagen IV levels is important for gon-1 suppression.

Genetic interactions among ADAMTS metalloproteases and basement membrane molecules in cell migration in Caenorhabditis elegans

During development of the Caenorhabditis elegans gonad, the gonadal leader cells, called distal tip cells (DTCs), migrate in a U-shaped pattern to form the U-shaped gonad arms. The ADAMTS (adisintegrin and metalloprotease with thrombospondin motifs) family metalloproteases MIG-17 and GON-1 are required for correct DTC migration. Mutations in mig-17 result in misshapen gonads due to the misdirected DTC migration, and mutations in gon-1 result in shortened and swollen gonads due to the premature termination of DTC migration. Although the phenotypes shown by mig-17 and gon-1 mutants are very different from one another, mutations that result in amino acid substitutions in the same basement membrane protein genes, emb-9/collagen IV a1, let-2/collagen IV a2 and fbl-1/fibulin-1, were identified as genetic suppressors of mig-17 and gon-1 mutants. To understand the roles shared by these two proteases, we examined the effects of the mig-17 suppressors on gon-1 and the effects of the gon-1 suppressors and enhancers on mig-17 gonadal defects. Some of the emb-9, let-2 and fbl-1 mutations suppressed both mig-17 and gon-1, whereas others acted only on mig-17 or gon-1. These results suggest that mig-17 and gon-1 have their specific functions as well as functions commonly shared between them for gonad formation. The levels of collagen IV accumulation in the DTC basement membrane were significantly higher in the gon-1 mutants as compared with wild type and were reduced to the wild-type levels when combined with suppressor mutations, but not with enhancer mutations, suggesting that the ability to reduce collagen IV levels is important for gon-1 suppression.

C. elegans as a model system to study the function of the COG complex in animal development

The conserved oligomeric Golgi (COG) complex is an octameric protein complex associated with the Golgi apparatus and is required for proper sorting and glycosylation of Golgi resident enzymes and secreted proteins. Although COG complex function has been extensively studied at the cellular and subcellular levels, its role in animal development mostly remains unknown. Recently, mutations in the components of the COG complex were found to cause abnormal gonad morphogenesis inCaenorhabditis elegans. InC. elegans, the COG complex acts in the glycosylation of an ADAM (a disintegrin and metalloprotease) family protein, MIG-17, which directs migration of gonadal distal tip cells to lead gonad morphogenesis. This is the first link between the COG complex and the function of an ADAM protease that is directly involved in organ morphogenesis, demonstrating the potential ofC. elegansas a model system to study COG function in animal development.

Multiple Signaling Mechanisms of the UNC-6/netrin Receptors UNC-5 and UNC-40/DCC in Vivo

Cell and growth cone migrations along the dorsoventral axis of Caenorhabditis elegans are mediated by the UNC-5 and UNC-40 receptor subtypes for the secreted UNC-6 guidance cue. To characterize UNC-6 receptor function in vivo, we have examined genetic interactions between unc-5 and unc-40 in the migrations of the hermaphrodite distal tip cells. We report that cell migration defects as severe as those associated with a null mutation in unc-6 are produced only by null mutations in both unc-5 and unc-40, indicating that either receptor retains some partial function in the absence of the other. We show that hypomorphic unc-5 alleles exhibit two distinct types of interallelic genetic interactions. In an unc-40 wild-type genetic background, some pairs of hypomorphic unc-5 alleles exhibit a partial allelic complementation. In an unc-40 null background, however, we observed that unc-5 hypomorphs exhibit dominant negative effects. We propose that the UNC-5 and UNC-40 netrin receptors can function to mediate chemorepulsion in DTC migrations either independently or together, and the observed genetic interactions suggest that this flexibility in modes of signaling results from the formation of a variety of oligomeric receptor complexes.