Development Genes and Evolution

, Volume 217, Issue 6, pp 449–458

A complement response may activate metamorphosis in the ascidian Boltenia villosa

  • Brock Roberts
  • Brad Davidson
  • Glen MacMaster
  • Victoria Lockhart
  • Eva Ma
  • Shannon Smith Wallace
  • Billie J. Swalla
Original Article

DOI: 10.1007/s00427-007-0157-0

Cite this article as:
Roberts, B., Davidson, B., MacMaster, G. et al. Dev Genes Evol (2007) 217: 449. doi:10.1007/s00427-007-0157-0

Abstract

Ascidian metamorphosis transforms a free-swimming larval chordate ascidian into a sessile adult through a distinct series of metamorphic events. Initially, larvae must become competent to respond to settlement cues. Settlement is then marked by dramatic body plan remodeling and may be accompanied by attachment to the substrate. Subtractive hybridization has revealed that many innate immunity transcripts are upregulated during metamorphosis in the ascidian Boltenia villosa. Several of these genes have well-known roles in the mannose-binding lectin (MBL)-complement pathway of innate immunity, including MBL and MBL-activated serine protease (MASP). MBL recognizes and binds to bacterial pathogens, activates MASP, and triggers the complement cascade. In B. villosa, larvae upregulate BvMASP at the time of competency to initiate settlement. We show that several bacterial strains can induce settlement and that the timing of BvMASP expression in the papillae-associated tissue (PAT) cells is tightly correlated with larval competency. We further demonstrate that serine protease inhibitors used to block the complement response also block metamorphosis, allowing tail resorption, but preventing further morphological changes. Based on these experiments, we propose that the MBL-complement pathway may be important for competency, bacterial substrate detection and body plan remodeling during metamorphosis.

Keywords

Ascidians Metamorphosis Larval settlement MASP Innate immunity 

Supplementary material

427_2007_157_Fig1_ESM.gif (98 kb)
Fig. S1

Alignment of ascidian MASP proteins with various chordate MASP sequences. A BvMASP protein fragment is shown aligned to gene duplication products in the ascidians C. intestinalis (CiMASP1-4) and Halocynthia roretzi (HrMASPa-b), and for amino acid sequences from four vertebrate MASP proteins (L. japonicum, X. laevis, M. musculus, H. sapiens) and one cephalochordate MASP (B. belcheri). We searched the C. intestinalis genome database with B. villosa MASP using a BLAST search program (http://genome.jgi-psf.org/ciona4/ciona4.home.html) and found matches to four MASP genes, designated CiMASP-1, CiMASP-2, CiMASP-3, and CiMASP-4. C. intestinalis genome analysis was conducted using the updated database at http://www.jgi.doe.gov/ciona. EST clones, corresponding to the four MASP-like proteins in the genome, were identified as ciad67l18 (CiMASP-1); ciad047i05 (CiMASP-2); ciad075 k07 (CiMASP-3); and ciad080h12 (CiMASP-4), although the ciad080h12 EST lacks a serine protease domain due to incomplete genome sequencing.

427_2007_157_Fig2_ESM.gif (7 kb)
Fig. S2

Two of the MASP genes in C. intestinalis appear to be a recent duplication. CiMASP-1 and CiMASP-2 (gene models ci0100133851 and ci0100133876, respectively) are found in close proximity on scaffold 69, suggesting that they are the product of a recent gene duplication. The transcriptional stop in the upstream gene, CiMASP-1, occurs 322 base pairs before the transcriptional start of CiMASP-2. CiMASP-1 and CiMASP-2 are shown in their relative orientation on scaffold 69. Black boxes represent exon regions. The base pair length of each exon is indicated above its corresponding box. Untranslated regions are represented by gray boxes at the 5′ and 3′ ends of both genes. Gene polarity and genomic coordinates are indicated beneath the chromosome model. The gray double-headed arrow denotes the 322 base pair gap between the transcriptional stop site of CiMASP-1 and the transcriptional start site of CiMASP-2 (GIF 7.07 KB)

Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  • Brock Roberts
    • 1
    • 2
  • Brad Davidson
    • 1
    • 2
  • Glen MacMaster
    • 1
    • 2
  • Victoria Lockhart
    • 1
    • 2
  • Eva Ma
    • 1
  • Shannon Smith Wallace
    • 1
  • Billie J. Swalla
    • 1
    • 2
  1. 1.Biology Department and Center for Developmental Biology, 24 Kincaid HallUniversity of WashingtonSeattleUSA
  2. 2.Friday Harbor LaboratoriesUniversity of WashingtonFriday HarborUSA
  3. 3.Department of Biological StructureUniversity of Washington School of MedicineSeattleUSA
  4. 4.Department of Cell Biology and AnatomyUniversity of ArizonaTucsonUSA