Retina-specific protein fascin 2 is an actin cross-linker associated with actin bundles in photoreceptor inner segments and calycal processes

Invest Ophthalmol Vis Sci. 2007 Mar;48(3):1380-8. doi: 10.1167/iovs.06-0763.

Abstract

Purpose: Fascin 2 is a retinal-specific member of the fascin family of actin filament-bundling proteins. Fascin 2 mutation in humans results in autosomal dominant retinitis pigmentosa or macular degeneration. To investigate the role of fascin 2 in photoreceptor survival, the authors examined its localization in photoreceptors and characterized its interactions with actin filaments in vitro.

Methods: Fascin 2 localization was determined by immunohistochemistry and transgenic expression of green fluorescent protein (GFP)-tagged fascin 2 in Xenopus laevis rods. Fascin 2 actin-binding and actin-bundling activity were examined in sedimentation assays using bacterially expressed fusion proteins and polymerized actin. To assess the role of phosphorylation of a conserved serine (amino acid 39) in fascin 2 on subcellular localization and actin-binding, effects of serine mutants were also examined in transgenic Xenopus and in in vitro assays.

Results: Fascin 2 is localized to actin filament bundles of the photoreceptor inner segment and calycal processes. Like fascin 1, fascin 2 binds and cross-links actin filaments. Mutation of serine 39 to an aspartic acid reduced fascin 2 binding of actin filaments and abolished fascin 2 bundling of actin filaments in vitro but produced no detectable effect on GFP-tagged fascin 2 localization in transgenic Xenopus.

Conclusions: These observations suggest that fascin 2 plays a role in the assembly or stabilization of inner segment and calycal process actin filament bundles in photoreceptors and that serine 39 phosphorylation reduces actin-binding and cross-linking activity and, thus, is likely to regulate the inner segment actin cytoskeleton.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Actin Cytoskeleton / metabolism*
  • Amino Acid Sequence
  • Animals
  • Animals, Genetically Modified
  • Blotting, Western
  • Cloning, Molecular
  • Eye Proteins / chemistry
  • Eye Proteins / metabolism*
  • Gene Expression
  • Green Fluorescent Proteins / genetics
  • Green Fluorescent Proteins / metabolism
  • Microfilament Proteins / chemistry
  • Microfilament Proteins / metabolism*
  • Microscopy, Fluorescence
  • Molecular Sequence Data
  • Phosphorylation
  • Photoreceptor Cells, Vertebrate / metabolism*
  • Recombinant Fusion Proteins
  • Serine / metabolism
  • Transgenes
  • Xenopus laevis
  • Zebrafish

Substances

  • Eye Proteins
  • FSCN2 protein, Xenopus
  • Microfilament Proteins
  • Recombinant Fusion Proteins
  • fscn2b protein, zebrafish
  • Green Fluorescent Proteins
  • Serine