Syndecan Regulates Cellular Morphogenesis in Cooperation with the Netrin Guidance Pathway and Rho-family GTPases

The establishment of complex cell shapes is essential for specific cellular functions, and thus critical in animal development and physiology. Heparan sulfate proteoglycans (HSPGs) are conserved glycoproteins that regulate interactions between extracellular signals and their receptors, to orchestrate morphogenetic events and elicit cellular responses. Although HSPG-regulated pathways have been implicated in regulating the guidance of neuronal migrations, whether HSPGs regulate earlier aspects of cellular development that dictate cell shape remains unknown. HSPGs consist of a protein core (e.g., Syndecan, Perlecan, Glypican, etc.) with attached heparan sulfate (HS) glycosaminoglycan chains, which are synthesized by glycosyltransferases of the exostosin family. Using mutations in the two C. elegans HS glycosyltransferases genes, rib-1 and rib-2, we reveal that HSPGs control the number of cellular projections in the epithelial excretory canal cell, which can form more than its normal four canals in these mutants. We identify SDN-1/Syndecan as the key HSPG that regulates the number of excretory canal cell projections in a cell-autonomous manner. We also find that Syndecan and guidance receptors for Netrin function in the same pathway to restrict the number of cellular projections. Furthermore, we show that the formation of extra projections in the absence of Syndecan requires the conserved Rho-family GTPases CED-10/Rac and MIG-2/RhoG. Our findings not only contribute to understanding the roles of conserved HSPGs in cellular morphogenetic events, but also reveal the existence of an HSPG-regulated system operating to guarantee that a precise number of cellular projections is established during cell development. Given the evolutionary conservation of developmental mechanisms and the molecules implicated, this work provides information relevant to understanding the cellular and molecular bases of the development of precise cellular morphologies in varied cell types across animals.

A Series of Tubes: The C. elegans Excretory Canal Cell as a Model for Tubule Development

Formation and regulation of properly sized epithelial tubes is essential for multicellular life. The excretory canal cell of C. elegans provides a powerful model for investigating the integration of the cytoskeleton, intracellular transport, and organismal physiology to regulate the developmental processes of tube extension, lumen formation, and lumen diameter regulation in a narrow single cell. Multiple studies have provided new understanding of actin and intermediate filament cytoskeletal elements, vesicle transport, and the role of vacuolar ATPase in determining tube size. Most of the genes discovered have clear homologues in humans, with implications for understanding these processes in mammalian tissues such as Schwann cells, renal tubules, and brain vasculature. The results of several new genetic screens are described that provide a host of new targets for future studies in this informative structure.

A tensile trilayered cytoskeletal endotube drives capillary-like lumenogenesis

Unicellular tubes are components of internal organs and capillaries. It is unclear how they meet the architectural challenge to extend a centered intracellular lumen of uniform diameter. In an RNAi-based Caenorhabditis elegans screen, we identified three intermediate filaments (IFs)—IFA-4, IFB-1, and IFC-2—as interactors of the lumenal membrane-actin linker ERM-1 in excretory-canal tubulogenesis. We find that IFs, generally thought to affect morphogenesis indirectly by maintaining tissue integrity, directly promote lumenogenesis in this capillary-like single-cell tube. We show that ERM-1, ACT-5/actin, and TBB-2/tubulin recruit membrane-forming endosomal and flux-promoting canalicular vesicles to the lumen, whereas IFs, themselves recruited to the lumen by ERM-1 and TBB-2, restrain lateral vesicle access. IFs thereby prevent cystogenesis, equilibrate the lumen diameter, and promote lumen forward extension. Genetic and imaging analyses suggest that IFB-1/IFA-4 and IFB-1/IFC-2 polymers form a perilumenal triple IF lattice, sandwiched between actin and helical tubulin. Our findings characterize a novel mechanism of capillary-like lumenogenesis, where a tensile trilayered cytoskeletal endotube transforms concentric into directional growth.

Mutations Affecting Nerve Attachment of Caenorhabditis elegans

Using a pan-neuronal GFP marker, a morphological screen was performed to detect Caenorhabditis elegans larval lethal mutants with severely disorganized major nerve cords. We recovered and characterized 21 mutants that displayed displacement or detachment of the ventral nerve cord from the body wall (Ven: ventral cord abnormal). Six mutations defined three novel genetic loci: ven-1, ven-2, and ven-3. Fifteen mutations proved to be alleles of previously identified muscle attachment/positioning genes, mup-4, mua-1, mua-5, and mua-6. All the mutants also displayed muscle attachment/positioning defects characteristic of mua/mup mutants. The pan-neuronal GFP marker also revealed that mutants of other mua/mup loci, such as mup-1, mup-2, and mua-2, exhibited the Ven defect. The hypodermis, the excretory canal, and the gonad were morphologically abnormal in some of the mutants. The pleiotropic nature of the defects indicates that ven and mua/mup genes are required generally for the maintenance of attachment of tissues to the body wall in C. elegans.

Taxonomy of Raphidascaris spp. (Nematoda, Anisakidae) of fishes, with a redescription of R. acus (Bloch, 1772)

Raphidascaris acus (Bloch, 1772) is redescribed from specimens from northern pike (Esox lucius) in Ontario. A reduced right excretory canal and a cuticular elevation in the ventral interlabial region are present. Hysterothylacium cayugensis Wigdor, 1918, Ascaris lucii Pearse, 1924, R. laurentianus Richardson, 1937, and R. alius Lyster, 1940 become junior synonyms of R. acus. The latter species, reported from a variety of fishes in Ontario and Quebec, is considered the only valid member of the genus in freshwater in North America and thus is distributed throughout the Holarctic. Four other species are considered valid: R. biwakoensis Fujita, 1928 (= R. gigi Fujita, 1928; = R. plecoglossi Fujita, 1928) from freshwater in Japan, and R. lutiani Olsen, 1952, R. chirocentri Yamaguti, 1935. and R. vicentei Santos, 1970 (= R. atlanticus Rodrigues, 1974; = R. yamagutii Vicente &Santos, 1974; = R. camura Deardorff &Overstreet, 1981) from marine fishes. The latter two species are similar if not identical and are broadly distributed in inshore subtropical oceans. The following are species inquirendae: R. adelinae (Condorelli-Francaviglia, 1898), R. anchoviellae Chandler, 1935, R. lophii (Wu, 1949), R. panijii Khan &Yassen, 1969, and R. synodi Paruchin, 1973. The broad host and geographic distributions of Raphidascaris spp. may indicate the genus is relatively old. The systematics of the Ascaridoidea is currently being revised. Reviews of other anisakid genera are necessary before relationships among Raphidascaris spp. and other genera can be determined.

Histochemical studies on Raillietina (Raillietina) johri (Cestoda: Davaineidae). III. Esterases

ABSTRACTNonspecific esterase (NSE), acetylcholinesterase (AChE) and pseudocholinesterase (ChE) have been localized by histochemical methods in various tissues of a cestode, Raillietina (Raillietina) johri obtained from the intestine of pigeon.NSE has been found in the rostellum, suckers, hooks, tegument, subtegumental muscle, excretory canal, cirrus sac, vagina and eggs. Two types of cells have been recognized on the scolex surface—some are NSE positive and others are NSE negative. AChE, besides being localized in nerves, has also been visualized in almost all the structures as in case of NSE except in hooks, excretory canal and eggs. Additionally AChE has been observed in the vas deferens and sperm ductules. ChE has been observed only in nerves, vas deferens, cirrus sac and vagina; the intensity of enzyme activity being low when compared with AChE. Possible involvement of these enzymes in the physiology of the parasite has been discussed.