The dauer larva of the nematode Caenorhabditis elegans is a good model system for investigating the regulation of developmental fates by environmental cues. Here we show that SDF-9, a protein tyrosine phosphatase-like molecule, is involved in the regulation of dauer larva formation. The dauer larva of sdf-9 mutants is different from a normal dauer larva but resembles the dauer-like larva of daf-9 and daf-12 dauer-constitutive mutants. Like these mutants, the dauer-constitutive phenotypes of sdf-9 mutants were greatly enhanced by cholesterol deprivation. Epistasis analyses, together with the relationship between sdf-9 mutations and daf-9 expression, suggested that SDF-9 increases the activity of DAF-9 or helps the execution of the DAF-9 function. SDF-9 was expressed in two head cells in which DAF-9 is expressed. By their position and by genetic mosaic experiments, we identified these cells as XXXL/R cells, which are known as embryonic hypodermal cells and whose function at later stages is unknown. Killing of the sdf-9-expressing cells in the wild-type first-stage larva induced formation of the dauer-like larva. Since this study on SDF-9 and former studies on DAF-9 showed that the functions of these proteins are related to those of steroids, XXXL/R cells seem to play a key role in the metabolism or function of a steroid hormone(s)that acts in dauer regulation.

Mutations in the a disintegrin and metalloprotease with thrombospondin motifs (ADAMTS) family of secreted proteases cause diseases linked to ECM abnormalities. However, the mechanisms by which these enzymes modulate the ECM during development are mostly unexplored. The Caenorhabditis elegans MIG-17/AD-AMTS protein is secreted from body wall muscle cells and localizes to the basement membrane (BM) of the developing gonad where it controls directional migration of gonadal leader cells. Here we show that specific amino acid changes in the ECM proteins fibulin-1C (FBL-1C) and type IV collagen (LET-2) result in bypass of the requirement for MIG-17 activity in gonadal leader cell migration in a nidogen (NID-1)-dependent and -independent manner, respectively. The MIG-17, FBL-1C and LET-2 activities are required for proper accumulation of NID-1 at the gonadal BM. However, mutant FBL-1C or LET-2 in the absence of MIG-17 promotes NID-1 localization. Furthermore, overexpression of NID-1 in mig-17 mutants substantially rescues leader cell migration defects. These results suggest that functional interactions among BM molecules are important for MIG-17 control of gonadal leader cell migration. We propose that FBL-1C and LET-2 act downstream of MIG-17-dependent proteolysis to recruit NID-1 and that LET-2 also activates a NID-1-independent pathway, thereby inducing the remodeling of the BM required for directional control of leader cell migration.ECM ͉ fibulin-1 ͉ organogenesis ͉ type IV collagen T he interaction between basement membranes (BMs) and migrating cells or the epithelial layer is a complicated but carefully controlled process that involves remodeling of the ECM. For example, the migration of border cells required for oogenesis and patterning of the early embryo in Drosophila melanogaster is accompanied by precise regulation of the synthesis and degradation of type IV collagen, laminin, and perlecan (1, 2). Fibronectin expression is required for branching morphogenesis of the submandibular salivary gland, lung, and kidney in mouse (3). However, the mechanisms of cell-ECM interactions and the roles of BMs in cell migration remain largely unknown.Gonadogenesis in the nematode Caenorhabditis elegans serves as a simple model system for elucidating the function of BMs in organ morphogenesis. The development of hermaphrodite gonads is regulated by the migration of gonadal distal tip cells (DTCs), which promote directional elongation of the gonad arms during the larval stages to form the U-shaped gonads found in adult animals (4, 5). Two secreted a disintegrin and metalloprotease with thrombospondin motifs (ADAMTS) family metalloproteases, MIG-17 and GON-1, are involved in this process. GON-1 is required for DTC motility, whereas MIG-17 controls the direction of DTC movement but does not control DTC motility per se (6, 7). MIG-17 is expressed in the body wall muscles and is localized to the BM of the gonad surface, where it is required for DTC migration (7,8). It has been proposed that MIG-17 and GON-1 remodel BMs via prote...

SUMMARYCytoskeletal regulation is important in cell migration. The Caenorhabditis elegans gonadal distal tip cells (DTCs) offer a simple model with which to investigate the mechanism of cell migration in organogenesis. Here, we report that one of the spectraplakin isoforms, VAB-10B1, plays an essential role in cell and nuclear migration of DTCs by regulating the actin and microtubule (MT) cytoskeleton. In the vab-10(tk27) mutant, which lacks VAB-10B1, alignment of filamentous (F)-actin and MTs was weakly and severely disorganized, respectively, which resulted in a failure to translocate the DTC nucleus and a premature termination of DTC migration. An MT growing-tip marker, EBP-2-GFP, revealed that polarized outgrowth of MTs towards the nuclei of migrating DTCs was strikingly impaired in tk27 animals. A vab-10 mini-gene encoding only the actin-and MT-binding domains significantly rescued the gonadal defects, suggesting that VAB-10B1 has a role in linking actin and MT filaments. These results suggest that VAB-10B1/spectraplakin regulates the polarized alignment of MTs, possibly by linking F-actin and MTs, which enables normal nuclear translocation and cell migration of DTCs.

Cytoskeletal regulation is important in cell migration. The Caenorhabditis elegans gonadal distal tip cells (DTCs) offer a simple model with which to investigate the mechanism of cell migration in organogenesis. Here, we report that one of the spectraplakin isoforms, VAB-10B1, plays an essential role in cell and nuclear migration of DTCs by regulating the actin and microtubule (MT) cytoskeleton. In the vab-10(tk27) mutant, which lacks VAB-10B1, alignment of filamentous (F)-actin and MTs was weakly and severely disorganized, respectively, which resulted in a failure to translocate the DTC nucleus and a premature termination of DTC migration. An MT growing-tip marker, EBP-2-GFP, revealed that polarized outgrowth of MTs towards the nuclei of migrating DTCs was strikingly impaired in tk27 animals. A vab-10 mini-gene encoding only the actin-and MT-binding domains significantly rescued the gonadal defects, suggesting that VAB-10B1 has a role in linking actin and MT filaments. These results suggest that VAB-10B1/spectraplakin regulates the polarized alignment of MTs, possibly by linking F-actin and MTs, which enables normal nuclear translocation and cell migration of DTCs.

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We previously reported on the use of enzymatic analysis to impair fatty acid metabolism followed by reduced myocardial energy content, leading to severe heart failure in adriamycin (ADR)-treated rats. The aim of this study is to investigate whether impaired myocardial energy metabolism can also be detected by other methods; i.e. measuring mitochondrial complex I activity and myocardial 125I-15-(p-iodophenyl)-3-(R,S)- methylpentadecanoic acid (BMIPP) accumulation in ADR-treated rats. Eight-week-old male Sprague-Dawley rats received 6 intraperitoneal injections of ADR (total 15 mg/kg: group ADR) or saline (control group) over 2 weeks. Left ventricular (LV) ejection fraction was assessed using echocardiography at 3- and 6-weeks after ADR injection (3 weeks and 6 weeks, respectively). Myocardial fatty acid utilization was assessed at 3 weeks and 6 weeks. The myocardial counts of BMIPP were measured after intravenous BMIPP (370 kBq) injection, and 125I counts were measured to calculate the uptake ratio. The enzymatic activity of complex I was assessed by monitoring the oxidation of nicotinamide-adenine-dinucleotide-disodium-salt (NADH). In rats treated with ADR, significant decrease in LV ejection fraction was observed only at 6 weeks compared to control (72.5 vs. 84.5%, p < 0.01). LV ejection fraction at 3 weeks was identical between group ADR and control (81.8 vs. 84.4%). However, at 3 weeks, complex I activity was already reduced significantly in group ADR as compared to control group (p = 0.03), but the reduction in BMIPP accumulation was not (p = 0.15). Our data indicated that reduced complex I activity in a phenomenon occurred in early phase of ADR-induced cardiomyopathy, and it might play an important role in the progression of ADR-induced heart failure.

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