Abstract
hSMP-1 is a human sperm membrane protein expressed during development. It is a testis-specific component produced during male germ cell differentiation. Proteins that interact with hSMP-1 were identified by the application of the yeast two-hybrid system. One of the components, RanBPM, was found to be associated with hSMP-1 under both in vitro and in vivo conditions. In the human testis, RanBPM is produced in spermatogonia and primary spermatocytes, suggesting expression during the early stages of spermatogenesis; whereas in the rat testis, it is located in round and elongated spermatids, similar to hSMP-1, suggesting expression of both components during spermiogenesis. Images obtained by immunofluorescence and confocal scanning microscopy of CHO-K1 cells co-transfected with pEGFP-C1-hSMP-1 and pDsRed1-Nl-RanBPM revealed that RanBPM and hSMP-1 are distributed in discrete loci throughout the cytoplasm. When superimposed, the stained spots appeared as congruent yellow areas, indicative of co-localization and probable complex formation of these two components. This interaction between hSMP-1 and RanBPM may be involved in the process of male germ cell differentiation. In CHO-Kl cells transfected with pEGFP-Cl-hSMP-1, the exogenously expressed hSMP-1 was found to co-localize with α-tubulin. Depolymerization of microtubules can be induced in CHO-Kl cells by cold treatment. In cells transfected with the pEGFP-Cl vector, the dispersed tubulins promptly reassembled upon warming. However, in cells transfected with pEGFP-Cl-hSMP-1, reassembly of the dispersed tubulins was blocked even upon rewarming of the cells. These findings suggest that hSMP-1 interacts with tubulins and thereby may modulate microtubule assembly and/or activity.
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Abbreviations
- RanBPM :
-
Ran binding protein in the microtubule organizing centre
- hSMP-1 :
-
Human sperm membrane protein
- MBP :
-
Maltose binding protein
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Acknowledgements
This study was supported by grants from the Special Fund for Major State Basic Research Project (G1999055901), National Natural Sciences Foundation of China (30070173, 30240019), State Ministry of Science and Technology Program (2002BA711A01), National High Technology Research and Development Plan of China (2001AA221131). The experimental study was performed in compliance with the laws of the People’s Republic of China.
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Tang, X., Zhang, J., Cai, Y. et al. Sperm membrane protein (hSMP-1) and RanBPM complex in the microtubule-organizing centre. J Mol Med 82, 383–388 (2004). https://doi.org/10.1007/s00109-004-0535-2
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DOI: https://doi.org/10.1007/s00109-004-0535-2