Translation and assembly of CABYR coding region B in fibrous sheath and restriction of calcium binding to coding region A

Dev Biol. 2005 Oct 1;286(1):46-56. doi: 10.1016/j.ydbio.2005.07.005.


CABYR is a highly polymorphic, sperm flagellar calcium-binding protein that is tyrosine as well as serine/threonine phosphorylated during capacitation. Six alternative splice variants of human CABYR (I-VI) have previously been identified, involving two coding regions, CR-A and CR-B, separated by an intervening stop codon. It is presently unknown if proteins encoded by the predicted coding region B of CABYR are translated during spermiogenesis, where they localize, or which CABYR isoforms bind calcium. Immunofluorescent and electron microscopic studies using polyclonal antibodies generated to the recombinant c-terminal 198 aa CABYR-B localized the isoforms containing CABYR-B to the ribs and longitudinal columns of the fibrous sheath in the principal piece of the flagellum. Antisera to recombinant CABYR-A and CABYR-B proteins recognized distinct populations of CABYR isoforms encoded by either CR-A alone and/or CR-B as well as a common population of CABYR isoforms. Only the recombinant CABYR-A and not the CABYR-B bound calcium in vitro, which is consistent with the hypothesis that CABYR-A is the only form that binds calcium in sperm. These observations confirmed that, despite the presence of the stop codon in CR-A, splice variants containing CR-B are expressed during spermiogenesis and assemble into the fibrous sheath of the principal piece; however, calcium binding occurs only to those CABYR isoforms containing CABYR-A.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Alternative Splicing
  • Animals
  • Antibodies
  • Base Sequence
  • Calcium / metabolism
  • Calcium-Binding Proteins / chemistry
  • Calcium-Binding Proteins / genetics*
  • Calcium-Binding Proteins / immunology
  • Calcium-Binding Proteins / metabolism*
  • Cloning, Molecular
  • Codon, Terminator
  • DNA, Complementary / genetics
  • Humans
  • Male
  • Microscopy, Electron
  • Phosphoproteins / chemistry
  • Phosphoproteins / genetics*
  • Phosphoproteins / immunology
  • Phosphoproteins / metabolism*
  • Polymorphism, Genetic
  • Protein Biosynthesis
  • Protein Isoforms / chemistry
  • Protein Isoforms / genetics
  • Protein Isoforms / metabolism
  • Rats
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / immunology
  • Recombinant Proteins / metabolism
  • Sperm Tail / metabolism*
  • Sperm Tail / ultrastructure
  • Spermatogenesis


  • Antibodies
  • CABYR protein, human
  • Calcium-Binding Proteins
  • Codon, Terminator
  • DNA, Complementary
  • Phosphoproteins
  • Protein Isoforms
  • Recombinant Proteins
  • Calcium