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Open Access Research article

Testis-expressed profilins 3 and 4 show distinct functional characteristics and localize in the acroplaxome-manchette complex in spermatids

Martina Behnen1, Kai Murk2, Petri Kursula3, Heike Cappallo-Obermann1, Martin Rothkegel2, Abraham L Kierszenbaum4 and Christiane Kirchhoff1*

Author affiliations

1 Department of Andrology, University Hospital Hamburg-Eppendorf, Hamburg, Germany

2 Zoological Institute, University of Braunschweig, Braunschweig, Germany

3 Department of Biochemistry, University of Oulu, Oulu, Finland

4 Department of Cell Biology and Anatomy, The City University of New York Medical School, New York, NY, USA

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Citation and License

BMC Cell Biology 2009, 10:34  doi:10.1186/1471-2121-10-34

Published: 6 May 2009

Abstract

Background

Multiple profilin isoforms exist in mammals; at least four are expressed in the mammalian testis. The testis-specific isoforms profilin-3 (PFN3) and profilin-4 (PFN4) may have specialized roles in spermatogenic cells which are distinct from known functions fulfilled by the "somatic" profilins, profilin-1 (PFN1) and profilin-2 (PFN2).

Results

Ligand interactions and spatial distributions of PFN3 and PFN4 were compared by biochemical, molecular and immunological methods; PFN1 and PFN2 were employed as controls. β-actin, phosphoinositides, poly-L-proline and mDia3, but not VASP, were confirmed as in vitro interaction partners of PFN3. In parallel experiments, PFN4 bound to selected phosphoinositides but not to poly-L-proline, proline-rich proteins, or actin. Immunofluorescence microscopy of PFN3 and PFN4 revealed distinct subcellular locations in differentiating spermatids. Both were associated first with the acroplaxome and later with the transient manchette. Predicted 3D structures indicated that PFN3 has the actin-binding site conserved, but retains only approximately half of the common poly-L-proline binding site. PFN4, in comparison, has lost both, polyproline and actin binding sites completely, which is well in line with the experimental data.

Conclusion

The testis-specific isoform PFN3 showed major hallmarks of the well characterized "somatic" profilin isoforms, albeit with distinct binding affinities. PFN4, on the other hand, did not interact with actin or polyproline in vitro. Rather, it seemed to be specialized for phospholipid binding, possibly providing cellular functions which are distinct from actin dynamics regulation.