The conserved oligomeric Golgi complex acts in organ morphogenesis via glycosylation of an ADAM protease in C. elegans

In C. elegans, the gonad acquires two U-shaped arms through directed migration of gonadal distal tip cells (DTCs). A member of the ADAM (a disintegrin and metalloprotease) family, MIG-17, is secreted from muscle cells and localizes to the gonadal basement membrane where it functions in DTC migration. Mutations in cogc-3 and cogc-1 cause misdirected DTC migration similar to that seen in mig-17 mutants. Here, we report that COGC-3 and COGC-1 proteins are homologous to mammalian COG-3/Sec34 and COG-1/ldlBp, respectively, two of the eight components of the conserved oligomeric Golgi (COG) complex required for Golgi function. Knockdown of any of the other six components by RNA interference also produces DTC migration defects, suggesting that the eight components function in a common pathway. COGC-3 and COGC-1 are required for the glycosylation and gonadal localization of MIG-17, but not for secretion of MIG-17 from muscle cells. Furthermore, COGC-3 requires MIG-17 activity for its action in DTC migration. Our findings demonstrate that COG complex-dependent glycosylation of an ADAM protease plays a crucial role in determining organ shape.     

Chondroitin acts in the guidance of gonadal distal tip cells in C. elegans

In Caenorhabditis elegans hermaphrodites, the U-shaped gonad arms are formed by directed migration of the gonadal distal tip cells (DTCs). The stereotyped pattern of DTC migration is carefully controlled by extracellular and cell surface molecules during larval development. Here we report that two proteins, SQV-5 (chondroitin synthase) and its cofactor MIG-22 (chondroitin polymerizing factor), are required for chondroitin biosynthesis and are essential for the dorsally guided migration of DTCs. We found that MIG-22 is expressed in migrating DTCs, hypodermal seam cells, developing vulva and oocytes. The expression of SQV-5 or MIG-22 in both DTCs and hypodermis rescued the DTC migration defects of the relevant mutants more efficiently than when they were expressed in either single tissue. Furthermore, the expression of SQV-5 by the mig-22 promoter significantly rescued sqv-5 mutants, implying that these two proteins act in the same tissues and that chondroitin proteoglycans produced in both of these tissues are required for DTC migration. The DTC migration defects caused by sqv-5 or mig-22 mutations were partially suppressed in the anterior and enhanced in the posterior DTCs in unc-6, unc-5 or unc-40 mutant backgrounds, suggesting that chondroitin proteoglycans play roles in the UNC-6/netrin-dependent guidance of DTCs.     

Role of the extracellular matrix in epithelial morphogenesis: A view from C. elegans

The extracellular matrix (ECM) plays an essential role in organizing tissues, defining their shapes or in presenting growth factors. Their components have been well described in most species, but our understanding of the mechanisms that control ECM remodeling remains limited. Likewise, how the ECM contributes to cellular mechanical responses has been examined in few cases. Here, I review how studies performed in C. elegans have brought several significant advances on those topics. Focusing only on epithelial cells, I discuss basement membrane invasion by the anchor cell during vulva morphogenesis, a process that has greatly expanded our knowledge of ECM remodeling in vivo. I then discuss the ECM role in a novel mechanotransduction process, whereby muscle contractions stimulate the remodeling of hemidesmosome-like junctions in the epidermis, which highlights that these junctions are mechanosensitive. Finally, I discuss progress in defining the composition and potential roles of the apical ECM covering epidermal cells in embryos.     

The roles of an ephrin and a semaphorin in patterning cell-cell contacts in C. elegans sensory organ development

Ephrins and semaphorins regulate a wide variety of developmental processes, including axon guidance and cell migration. We have studied the roles of the ephrin EFN-4 and the semaphorin MAB-20 in patterning cell-cell contacts among the cells that give rise to the ray sensory organs of Caenorhabditis elegans. In wild-type, contacts at adherens junctions form only between cells belonging to the same ray. In efn-4 and mab-20 mutants, ectopic contacts form between cells belonging to different rays. Ectopic contacts also occur in mutants in regulatory genes that specify ray morphological identity. We used efn-4 and mab-20 reporters to investigate whether these ray identity genes function through activating expression of efn-4 or mab-20 in ray cells. mab-20 reporter expression in ray cells was unaffected by mutants in the Pax6 homolog mab-18 and the Hox genes egl-5 and mab-5, suggesting that these genes do not regulate mab-20 expression. We find that mab-18 is necessary for activating efn-4 reporter expression, but this activity alone is not sufficient to account for mab-18 function in controlling cell-cell contact formation. In egl-5 mutants, efn-4 reporter expression in certain ray cells was increased, inconsistent with a simple repulsion model for efn-4 action. The evidence indicates that ray identity genes primarily regulate ray morphogenesis by pathways other than through regulation of expression of semaphorin and ephrin.     

Transcriptional control and patterning of the pho-1 gene, an essential acid phosphatase expressed in the C. elegans intestine

We have previously described an acid phosphatase enzyme, PHO-1, present at the lumenal surface of all but the anterior six cells of the Caenorhabditis elegans intestine. In the present paper, we identify the pho-1 structural gene, which encodes a histidine acid phosphatase showing highest similarity to human prostatic acid phosphatase. The pho-1 5'-flanking DNA is capable of directing reporter gene expression that is both gut specific, correctly timed and correctly "patterned", that is, not expressed in the gut anterior. Furthermore, this anterior-posterior patterning of pho-1 expression responds to the C. elegans Wnt pathway as if pho-1 is repressed (directly or indirectly) by high levels of the HMG effector protein POP-1. Transgenic analysis of the pho-1 promoter shows that gut expression is critically dependent on a single WGATAR site. The gut-specific GATA factor ELT-2 binds to this site in vitro and removal of ELT-2 from the embryo destroys expression of the pho-1 reporter. Thus, all our results indicate that pho-1 is a direct downstream target of ELT-2. Finally, the pho-1 loss-of-function mutation shows an interesting and unexpected phenotype for a somatically-expressed hydrolytic enzyme: loss of pho-1 causes arrest of the majority of embryos but this lethality is a maternal effect. We suggest that pho-1 is required by the maternal intestine to assimilate some nutrient or cleavage product that is subsequently provided to the next generation of embryos.     

Aberrant,ectopic expression of VEGF and VEGF receptors 1 and 2 in malignant colonic epithelial cells. Implications for these cells growth via an autocrine mechanism

Vascular endothelial growth factor A (referred to as VEGF) is implicated in colon cancer growth. Currently, the main accepted mechanism by which VEGF promotes colon cancer growth is via the stimulation of angiogenesis, which was originally postulated by late Judah Folkman. However, the cellular source of VEGF in colon cancer tissue; and, the expression of VEGF and its receptors VEGF-R1 and VEGF-R2 in colon cancer cells are not fully known and are subjects of controversy.