title: Interaction of the retinoic acid signaling pathway with spicule formation in the marine sponge Suberites domuncula through activation of bone morphogenetic protein-1.
abstract: BACKGROUND
  The formation of the spicules in siliceous sponges involves the formation of cylinder-like structures in the extraspicular space, composed of the enzyme silicatein and the calcium-dependent lectin.
  
  
  METHODS
  Molecular cloning of the cDNAs (carotene dioxygenase, retinal dehydrogenase, and BMB-1 [bone morphogenic protein-1]) from the demosponge Suberites domuncula was performed. These tools were used to understand the retinoid metabolism in the animal by qRT-PCR, immunoblotting and TEM.
  
  
  CONCLUSIONS
  We demonstrate that silintaphin-2, a silicatein-interacting protein, is processed from a longer-sized 15-kDa precursor to a truncated, shorter-sized 13kDa calcium-binding protein via proteolytic cleavage at the dipeptide Ala↓Asp, mediated by BMP-1. The expression of this protease as well as the expression of two key enzymes of the carotinoid metabolism, the β,β-carotene-15,15'-dioxygenase and the retinal dehydrogenase/reductase, were found to be strongly up-regulated by retinoic acid. Hence retinoic acid turned out to be a key factor in skeletogenesis in the most ancient still existing metazoans, the sponges.
  
  
  CONCLUSIONS
  It is shown that retinoic acid regulates the formation of the organic cylinder that surrounds the axis of the spicules and enables, as a scaffold, the radial apposition of new silica layers and hence the growth of the spicules.
authors.affiliation: ERC Advanced Grant Research Group, Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University Mainz, Germany. wmueller@uni-mainz.de
authors.forename: Werner E G
authors.initials: WE
authors.lastname: Müller
authors.forename: Michael
authors.initials: M
authors.lastname: Binder
authors.forename: Johannes
authors.initials: J
authors.lastname: von Lintig
authors.forename: Yue-Wei
authors.initials: YW
authors.lastname: Guo
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Wang
authors.forename: Jaap A
authors.initials: JA
authors.lastname: Kaandorp
authors.forename: Matthias
authors.initials: M
authors.lastname: Wiens
authors.forename: Heinz C
authors.initials: HC
authors.lastname: Schröder
mesh_terms: D000818:Animals; D001483:Base Sequence; D055395:Bone Morphogenetic Protein 1 / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D017931:DNA Primers; D008386:Marine Biology; D008969:Molecular Sequence Data; D011161:Porifera / Q000378:metabolism* / Q000382:microbiology; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction; D014212:Tretinoin / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D014212:Tretinoin; D055395:Bone Morphogenetic Protein 1