EDSINGER-GONZALES, Eric; SMITH, Shannon; SWALLA, Billie; University of Washington; University of Washington; University of Washington: The MBL-Complement pathway of innate immunity and its role in larval settlement and metamorphosis in the ascidian Boltenia villosa.
The MBL-Complement pathway of innate immunity functions in bacterial recognition in deuterostomes. Bacterial and other environmental cues are commonly utilized by the swimming larval stages of benthic adults for microhabitat selection and the associated induction of larval settlement and metamorphosis. Detection of settlement cues in ascidians is thought to involve neural structures and an anterior EGF pathway involving MAPK and the release of nitric oxide. Coordination of settlement cue detection and the activation of downstream pathways remain unclear. Our lab has recently shown in tadpoles of the ascidian Boltenia villosa that various members of the MBL-Complement pathway are expressed at the onset of larval competence, dramatically upregulated by the induction of settlement and then rapidly down-regulated following the onset of metamorphosis. This suggests that the MBL-Complement pathway of innate immunity represents a third, previously unrecognized aspect of larval settlement and metamorphosis in ascidians. We have examined the gene expression of various MBL-Complement pathway members in detail before larval competence, during and following settlement. We demonstrate a functional linkage between the MBL-Complement pathway and metamorphosis using serine protease inhibitors. To begin integrating the different pathways of settlement and metamorphosis, we looked at the expression and function of MBL-Complement pathway genes in the context of the EGF and Nitric oxide pathways. Further comparative studies integrating the ecology, development and evolution of ascidian life-histories are required to further unravel and understand the conservation and co-option of the MBL-Complement pathway of bacterial recognition in larval metamorphosis and adult innate immunity.
