An axonemal dynein particularly important for flagellar movement at high viscosity. Implications from a new Chlamydomonas mutant deficient in the dynein heavy chain gene DHC9

Ciliary and flagellar axonemes contain multiple inner arm dyneins of which the functional difference is largely unknown. In this study, a Chlamydomonas mutant, ida9, lacking inner arm dynein c was isolated and shown to carry a mutation in the DHC9 dynein heavy chain gene. The cDNA sequence of DHC9 was determined, and its information was used to show that >80% of it is lost in the mutant. Electron microscopy and image analysis showed that the ida9 axoneme lacked electron density near the base of the S2 radial spoke, indicating that dynein c localizes to this site. The mutant ida9 swam only slightly slower than the wild type in normal media. However, swimming velocity was greatly reduced when medium viscosity was modestly increased. Thus, dynein c in wild type axonemes must produce a significant force when flagella are beating in viscous media. Because motility analyses in vitro have shown that dynein c is the fastest among all the inner arm dyneins, we can regard this dynein as a fast yet powerful motor.     

Specific sequences in the N and C termini of apolipoprotein A-IV modulate its conformation and lipid association

Apolipoprotein (apoA-IV) is a 376-residue exchangeable apolipoprotein that may play a number of important roles in lipid metabolism, including chylomicron assembly, reverse cholesterol transport, and appetite regulation. In vivo, apoA-IV exists in both lipid-poor and lipid-associated forms, and the balance between these states may determine its function. We examined the structural elements that modulate apoA-IV lipid binding by producing a series of deletion mutants and determining their ability to interact with phospholipid liposomes. We found that the deletion of residues 333-343 strongly increased the lipid association rate versus native apoA-IV. Additional mutagenesis revealed that two phenylalanine residues at positions 334 and 335 mediated this lipid binding inhibitory effect. We also observed that residues 11-20 in the N terminus were required for the enhanced lipid affinity induced by deletion of the C-terminal sequence. We propose a structural model in which these sequences can modulate the conformation and lipid affinity of apoA-IV.     

The mouse ortholog of EFHC1 implicated in juvenile myoclonic epilepsy is an axonemal protein widely conserved among organisms with motile cilia and flagella

The gene product of EFHC1 recently implicated in juvenile myoclonic epilepsy (JME) was found to be a homolog of Chlamydomonas axonemal protein Rib72, whose homologs are present in a wide variety of organisms that have motile cilia and flagella. Western blot analyses and immunofluorescence localization of the mouse ortholog mRib72-1/Efhc1 indicated that it is indeed abundantly present in sperm flagella and tracheal cilia but only in a small amount in the brain. It is not present in immotile primary cilia. These observations raise the possibility that malfunction of motile cilia is involved in the development of JME.     

Effects of the core lipid on the energetics of binding of ApoA-I to model lipoprotein particles of different sizes

Interaction of apolipoproteins (apo) with lipid surfaces plays crucial roles in lipoprotein metabolism and cholesterol homeostasis. To elucidate the thermodynamics of binding of apoA-I to lipid, we used lipid emulsions composed of triolein (TO) and egg phosphatidylcholine (PC) as lipoprotein models. Determination of the level of binding of wild-type (WT) apoA-I and some deletion mutants to large (120 nm diameter; LEM) and small (35 nm diameter; SEM) emulsions indicated that N-terminal (residues 44-65) and C-terminal (residues 190-243 and 223-243) deletions have large effects on lipid interaction, whereas deletion of the central region (residues 123-166) has little effect. Substitution of amino acids at either L230 or L230, L233, and Y236 with proline residues also decreases the level of binding, indicating that an alpha-helix conformation in this C-terminal region is required for efficient lipid binding. Calorimetry showed that binding of WT apoA-I to SEM generates endothermic heat (DeltaH approximately 30 kcal/mol) in contrast to the exothermic heat (ca. -85 kcal/mol) generated upon binding to LEM and egg PC small unilamellar vesicles (SUV). This exothermic heat arises from an approximately 25% increase in alpha-helix content, and it drives the binding of apoA-I to LEM and SUV. There is a similar increase in alpha-helix content of apoA-I upon binding to either SEM or SUV, but the binding of apoA-I to SEM is an entropy-driven process. These results suggest that the presence of a core triglyceride modifies the highly curved SEM surface packing and thereby the thermodynamics of apoA-I binding in a manner that compensates for the exothermic heat generated by alpha-helix formation.     

Prenatal blockage of lymphotoxin beta receptor and TNF receptor p55 signaling cascade resulted in the acceleration of tissue genesis for isolated lymphoid follicles in the large intestine

Signaling by lymphotoxin (LT) and TNF is essential for the organogenesis of secondary lymphoid tissues in systemic and mucosal compartments. In this study, we demonstrated that the progeny of mice treated with fusion protein of LTbetaR and IgGFc (LTbetaR-Ig) or LTbetaR-Ig plus TNFR55-Ig (double Ig) showed significantly increased numbers of isolated lymphoid follicles (ILF) in the large intestine. Interestingly, double Ig treatment accelerated the maturation of large intestinal ILF. Three-week-old progeny of double Ig-treated mice showed increased numbers of ILF in the large intestine, but not in the small intestine. Furthermore, alteration of intestinal microflora by feeding of antibiotic water did not affect the increased numbers of ILF in the large intestine of double Ig-treated mice. Most interestingly, mice that developed numerous ILF also had increased levels of activation-induced cytidine deaminase expression and numbers of IgA-expressing cells in the lamina propria of the large intestine. Taken together, these results suggest that ILF formation in the large intestine is accelerated by blockage of LTbetaR and TNFR55 signals in utero, and ILF, like colonic patches, might play a role in the induction of IgA response in the large intestine.     

New and highly efficient method for silkworm transgenesis using Autographa californica nucleopolyhedrovirus and piggyBac transposable elements

We have developed a new method for the transgenesis of the silkworm, Bombyx mori. This method couples the use of recombinant baculoviruses with the use of the piggyBac transposable element. One recombinant AcNPV, designated the helper virus, is designed to express the piggyBac transposase under the control of the Drosophila hsp70 promoter. Another recombinant AcNPV encoded the gene to be incorporated into the silkworm genome, in this case a green fluorescent protein (GFP) gene, under the control of B. mori actin A3 promoter and franked by the piggyBac inverted terminal repeats. Preblastoderm eggs were inoculated with a fine needle coated with a mixture of these two recombinant baculoviruses. Most of the inoculated larvae hatched and a high proportion of the newly hatched G0 larvae expressed the GFP marker. Transgenesis was confirmed by Southern blot analysis of G1 insects, sequencing the insertion site junctions isolated by inverse PCR, and the marker segregated in Mendelian fashion, as evidenced by the appearance of green fluorescence in G2 insects. Thus, transgenic silkworms were easily and efficiently obtained using this new method.     

Scavenger receptor expressed by endothelial cells I (SREC-I) mediates the uptake of acetylated low density lipoproteins by macrophages stimulated with lipopolysaccharide

Scavenger receptor expressed by endothelial cells I (SREC-I) is a novel endocytic receptor for acetylated low density lipoprotein (LDL). Here we show that SREC-I is expressed in a wide variety of tissues, including macrophages and aortas. Lipopolysaccharide (LPS) robustly stimulated the expression of SREC-I in macrophages. In an initial attempt to clarify the role of SREC-I in the uptake of modified lipoproteins as well as in the development of atherosclerosis, we generated mice with a targeted disruption of the SREC-I gene by homologous recombination in embryonic stem cells. To exclude the overwhelming effect of the type A scavenger receptor (SR-A) on the uptake of Ac-LDL, we further generated mice lacking both SR-A and SREC-I (SR-A(-/-);SREC-I(-/-)) by cross-breeding and compared the uptake and degradation of Ac-LDL in the isolated macrophages. The contribution of SR-A and SREC-I to the overall degradation of Ac-LDL was 85 and 5%, respectively, in a non-stimulated condition. LPS increased the uptake and degradation of Ac-LDL by 1.8-fold. In this condition, the contribution of SR-A and SREC-I to the overall degradation of Ac-LDL was 90 and 6%, respectively. LPS increased the absolute contribution of SR-A and SREC-I by 1.9- and 2.3-fold, respectively. On the other hand, LPS decreased the absolute contribution of other pathways by 31%. Consistently, LPS did not increase the expression of other members of the scavenger receptor family such as CD36. In conclusion, SREC-I serves as a major endocytic receptor for Ac-LDL in LPS-stimulated macrophages lacking SR-A, suggesting that it has a key role in the development of atherosclerosis in concert with SR-A.     

ADAMs, a disintegrin and metalloproteinases, mediate shedding of oxytocinase

Placental leucine aminopeptidase (P-LAP), a type-II transmembrane protease responsible for oxytocin degradation during pregnancy, is converted to a soluble form through proteolytic cleavage. The goal of this study was to determine the nature of the P-LAP secretase activity. The hydroxamic acid-based metalloprotease inhibitors GM6001 and ONO-4817 as well as the TNF-alpha protease inhibitor-2 (TAPI-2) reduced P-LAP release, while tissue inhibitors of metalloproteinase (TIMP)-1 and TIMP-2, which are matrix metalloproteinase inhibitors, had no effect on P-LAP release in Chinese hamster ovary (CHO) cells stably overexpressing P-LAP, thus indicating possible involvement of ADAM (a disintegrin and metalloproteinase) members in P-LAP shedding. Furthermore, overexpression of ADAM9 and ADAM12 increased P-LAP release in P-LAP-CHO transfectants. Immunohistochemical analysis in human placenta demonstrated strong expression of ADAM12 in syncytiotrophoblasts, while little expression of ADAM9 was detected throughout the placenta. Our results suggest ADAM members, at least including ADAM12, are involved in P-LAP shedding in human placenta.     

Role of gut-associated lymphoreticular tissues in antigen-specific intestinal IgA immunity

This study assessed the roles of the postnatal lymphotoxin-beta receptor (LTbetaR)-mediated signals in the gut-associated lymphoreticular tissues of mice for subsequent regulation of Ag-specific intestinal IgA responses. Blockade of LTbetaR-dependent events by postnatal administration of the fusion protein of LTbetaR and IgG Fc (LTbetaR-Ig) reduced both the size and numbers of Peyer's patches (PP) without influencing the PP microarchitecture. Interestingly, inhibition of LTbetaR-dependent signaling revealed significant reductions in the formation of follicular dendritic cell clusters in mesenteric lymph nodes (MLN). Furthermore, these postnatal signaling events controlled the development of isolated lymphoid follicles (ILF) because treatment with LTbetaR-Ig eliminated the formation of ILF. LTbetaR-Ig-treated mice with altered microarchitecture of MLN and lacking ILF were still able to produce significant Ag-specific mucosal IgA responses after oral immunization; however, the levels were significantly lower than those seen in control mice. These results imply the importance of ILF for Ag-specific intestinal immunity. However, mice treated with both TNFR55-Ig and LTbetaR-Ig in utero, which lack PP and MLN, but retain intact ILF, failed to induce Ag-specific IgA responses after oral immunization. These findings demonstrate that ILF are not essential for induction of intestinal IgA Ab responses to orally administered Ag. Furthermore, the induction of intestinal IgA Ab responses requires the proper maintenance of the MLN microarchitecture, including a follicular dendritic cell network.