Sandra Schmieder

Relics of ancient infections are abundant in eukaryote genomes, but little is known about how they evolve when they confer a functional benefit on their host. We show here, for the first time, that the virus-like particles shown to protect Venturia canescens eggs against host immunity are derived from a nudivirus genome incorporated by the parasitic wasp into its own genetic material. Nudivirus hijacking was also at the origin of protective particles from braconid wasps. However, we show here that the viral genes produce “liposomes” that wrap and deliver V. canescens virulence proteins, whereas the particles are used as gene transfer agents in braconid wasps. Our findings indicate that virus domestication has occurred repeatedly during parasitic wasp evolution but with different evolutionary trajectories after endogenization, resulting in different virulence molecule delivery strategies.

In several Hymenoptera, sexual fate is determined by the allelic composition at the complementary sex-determiner locus, a sex-determination mechanism that can strongly affect population dynamics. To date, the molecular identification of complementary sex determiner has only been achieved in the honeybee, where the complementary sex-determiner gene was reported to have arisen from duplication of the feminizer gene. Strikingly, the complementary sex-determiner gene was also proposed to be unique to the honeybee lineage. Here we identify feminizer and complementary sex-determiner orthologues in bumble bees and ants. We further demonstrate that the duplication of feminizer that produced complementary sex determiner occurred before the divergence of Aculeata species (~120 Myr ago). Finally, we provide evidence that the two genes evolved concertedly through gene conversion, complementary sex-determiner evolution being additionally shaped by mosaic patterns of selection. Thus, the complementary sex-determiner gene likely represents the molecular basis for single locus-complementary sex determination in the Aculeata infra-order, and possibly, in the entire Hymenoptera order.

Background: Brain-expressed genes that were created in primate lineage represent obvious candidates to investigate molecular mechanisms that contributed to neural reorganization and emergence of new behavioural functions in Homo sapiens. PMCHL1 arose from retroposition of a pro-melanin-concentrating hormone (PMCH) antisense mRNA on the ancestral human chromosome 5p14 when platyrrhines and catarrhines diverged. Mutations before divergence of hylobatidae led to creation of new exons and finally PMCHL1 duplicated in an ancestor of hominids to generate PMCHL2 at the human chromosome 5q13. A complex pattern of spliced and unspliced PMCHL RNAs were found in human brain and testis. Results: Several novel spliced PMCHL transcripts have been characterized in human testis and fetal brain, identifying an additional exon and novel splice sites. Sequencing of PMCHL genes in several non-human primates allowed to carry out phylogenetic analyses revealing that the initial retroposition event took place within an intron of the brain cadherin (CDH12) gene, soon after platyrrhine/catarrhine divergence, i.e. 30–35 Mya, and was concomitant with the insertion of an AluSg element. Sequence analysis of the spliced PMCHL transcripts identified only short ORFs of less than 300 bp, with low (VMCH-p8 and protein variants) or no evolutionary conservation. Western blot analyses of human and macaque tissues expressing PMCHL RNA failed to reveal any protein corresponding to VMCH-p8 and protein variants encoded by spliced transcripts. Conclusion: Our present results improve our knowledge of the gene structure and the evolutionary history of the primate-specific chimeric PMCHL genes. These genes produce multiple spliced transcripts, bearing short, non-conserved and apparently non-translated ORFs that may function as mRNA-like non-coding RNAs.

Mutations in the gene encoding ClC‐5 lead to X‐linked hypercalciuric nephrolithiasis (XLHN), characterized by proteinuria, hypercalciuria, and phosphaturia. In renal proximal tubule cells, ClC‐5 was identified as an important player in endocytosis, which ensures reabsorption of filtered protein. However, the recent finding that ClC‐5 is a Cl⁻/H⁺ antiporter and not a Cl⁻ channel as long thought points to the lack of understanding of its functional role. Also, little biochemical data are available about ClC‐5 and its post‐translational modifications have not been investigated. Here, we examined the role of N‐glycosylation of xClC‐5 in the Xenopus oocyte expression system by comparing wild‐type (WT) xClC‐5 and N‐glycosylation site mutants. We found that xClC‐5 is N‐glycosylated on asparagines 169 and 470, which are the only N‐glycosylated sites. xClC‐5 mutants have an increased susceptibility to polyubiquitination and proteasomal degradation; however, without a notable impact on the expression level. Using a cross‐linking reagent, we showed that xClC‐5 assembles into protein complexes, independent of its N‐glycosylation. Voltage‐clamp measurements showed a reduced conductance in the presence of tunicamycin and with xClC‐5 N‐glycosylation site mutants. Using immunocytochemistry, we localized xClC‐5 mainly in intracellular compartments, and found that its cell surface pool is reduced in the absence of N‐glycans. We further examined the plasma membrane retrieval of WT and mutant xClC‐5 in the presence of Brefeldin A (BFA), and found that the non‐glycosylated mutant was retrieved more than five times faster than the WT protein. We conclude that N‐glycosylation enhances cell surface expression of xClC‐5, increasing its plasma membrane transport activity. J. Cell. Physiol. 210: 479–488, 2007.

Podocalyxin (PC) is the major sialoglycoprotein expressed on the apical membrane of the podocyte. Previously it was shown that PC is connected to actin through the PC/NHERF2/ezrin complex, and this connection is disrupted in the nephrotic syndrome. For assessing whether expression of PC affects the organization of the actin cytoskeleton, MDCK cell lines stably expressing either full-length PC or a PC mutant lacking the NHERF binding site was established. It was found that full-length PC but not the PC mutant is connected to actin, induces redistribution of actin toward the apical membrane, and leads to increased RhoA activity. By immunofluorescence redistribution of RhoA and RhoGDI was observed in the presence of both full-length PC and the PC mutant. With the use of pulldown assays, PC and ezrin were found to interact directly and the ezrin binding site was mapped to the juxtamembrane region of PC’s cytoplasmic tail. It is concluded that PC binds to ezrin both directly and indirectly. PC activates RhoA through NHERF and ezrin, leading to redistribution of actin filaments. These results suggest that in podocytes, PC may also regulate foot process architecture through RhoA.

We investigated the role of taurine in cell homeostasis and characterized the taurine transport pathway in cultured kidney cells (A6). The taurine concentration in A6 cells varies with the osmolarity of the culture medium, suggesting that taurine participates in cell osmolarity. Under isosmotic conditions, 14C-taurine efflux through the apical membranes (aJtaur) was 6–7 times lower than that through the basolateral membranes (bJtaur). Under hyposmotic conditions, aJtaur remained almost unchanged. On the contrary, bJtaur increased 8 times in comparison with isosmotic conditions. In hyposmotic conditions, bJtaur was inhibited by 500 mM DIDS, 50 mM NPPB, 10 mM of the two oxonol derivatives DISBAC(2)3 and WW-791, and 100 mM ketoconazole. Conversely, 100 mM 1,9-dideoxyforskolin, 10 mM tamoxifen, 100 mM niflumic acid and 50 mM verapamil had no inhibitory effects. Cell volume regulation upon hyposmotic stress was also found to be inhibited by DISBAC(2)3 (K0.5 of 5±1 mM) and by ketoconazole. Nystatin was used to permeabilize the apical membranes with the aim to further characterize bJtaur. 14C-taurine transepithelial fluxes in nystatin-treated cells were found to be linear over taurine concentrations ranging from 3.5 mM to 35 mM. Clamping the transepithelial voltage at positive values (serosal side) slightly stimulated the 14C-taurine transport. Similar time courses of 14C-taurine, 36Cl and 86Rb transepithelial fluxes were found under osmotic stimulation followed by DIDS inhibition in nystatin-treated cells. In whole cell patch-clamp experiments, DISBAC(2)3 application resulted in a strong and reversible decrease of the global Cl? current which was stimulated by hyposmotic stress. Our study indicates that taurine participates in the control of A6 cell osmolarity and that the transporting taurine pathway (efflux) is on the basolateral membranes. In addition to usual chloride channel blockers, oxonol was found to be a potent blocker of the taurine transport and of the swelling-activated chloride current. Using a pharmacological approach, we could not distinguish between a common or different pathway for Cl? and taurine.