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Synaptopodin: an actin-associated protein in telencephalic dendrites and renal podocytes.

Mundel P, Heid HW, Mundel TM, Krüger M, Reiser J, Kriz W - J. Cell Biol. (1997)

Bottom Line: In particular, synaptopodin does not contain functional domains found in receptor-clustering PSD proteins.The exclusive synaptopodin synthesis in the telencephalon has been confirmed by in situ hybridization, where synaptopodin mRNA is only found in perikarya of the olfactory bulb, cerebral cortex, striatum, and hippocampus, i.e., the expression is restricted to areas of high synaptic plasticity.From these results and experiments with cultured cells we conclude that synaptopodin represents a novel kind of proline-rich, actin-associated protein that may play a role in modulating actin-based shape and motility of dendritic spines and podocyte foot processes.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy and Cell Biology, University of Heidelberg, Germany. peter.mundel@urz.uni-heidelberg.de

ABSTRACT
Synaptopodin is an actin-associated protein of differentiated podocytes that also occurs as part of the actin cytoskeleton of postsynaptic densities (PSD) and associated dendritic spines in a subpopulation of exclusively telencephalic synapses. Amino acid sequences determined in purified rat kidney and forebrain synaptopodin and derived from human and mouse brain cDNA clones show no significant homology to any known protein. In particular, synaptopodin does not contain functional domains found in receptor-clustering PSD proteins. The open reading frame of synaptopodin encodes a polypeptide with a calculated Mr of 73.7 kD (human)/74.0 kD (mouse) and an isoelectric point of 9.38 (human)/9. 27 (mouse). Synaptopodin contains a high amount of proline ( approximately 20%) equally distributed along the protein, thus virtually excluding the formation of any globular domain. Sequence comparison between human and mouse synaptopodin revealed 84% identity at the protein level. In both brain and kidney, in vivo and in vitro, synaptopodin gene expression is differentiation dependent. During postnatal maturation of rat brain, synaptopodin is first detected by Western blot analysis at day 15 and reaches maximum expression in the adult animal. The exclusive synaptopodin synthesis in the telencephalon has been confirmed by in situ hybridization, where synaptopodin mRNA is only found in perikarya of the olfactory bulb, cerebral cortex, striatum, and hippocampus, i.e., the expression is restricted to areas of high synaptic plasticity. From these results and experiments with cultured cells we conclude that synaptopodin represents a novel kind of proline-rich, actin-associated protein that may play a role in modulating actin-based shape and motility of dendritic spines and podocyte foot processes.

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Expression of synaptopodin in cultured hippocampal neurons. (a) In 25-d-old cultured hippocampal neurons, a dotted pattern of immunoreactivity in dendrites is seen, whereas axons (arrows) are not labeled. (b) Phase contrast microscopy. (c) Confocal laser  scanning double fluorescence analysis of synaptopodin (red) and MAP2 (green) to demonstrate the exclusive expression of synaptopodin in dendrites. (d) Confocal laser scanning double fluorescence analysis of synaptopodin and synaptophysin. The yellow signal results  from a complete overlap of the immunoreactivity and proves the synaptic localization of synaptopodin in cultured neurons. Bar, 10 μm.
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Figure 10: Expression of synaptopodin in cultured hippocampal neurons. (a) In 25-d-old cultured hippocampal neurons, a dotted pattern of immunoreactivity in dendrites is seen, whereas axons (arrows) are not labeled. (b) Phase contrast microscopy. (c) Confocal laser scanning double fluorescence analysis of synaptopodin (red) and MAP2 (green) to demonstrate the exclusive expression of synaptopodin in dendrites. (d) Confocal laser scanning double fluorescence analysis of synaptopodin and synaptophysin. The yellow signal results from a complete overlap of the immunoreactivity and proves the synaptic localization of synaptopodin in cultured neurons. Bar, 10 μm.

Mentions: We next analyzed the expression of synaptopodin in cultured neurons derived from embryonic 18-d-old rat hippocampi. The expression started at day 12 in vitro, increased thereafter in parallel with process and spine formation, and reached its maximum expression after 25 d in vitro (Fig. 10 a). Like in vivo, synaptopodin was only found in dendrites as revealed in double labeling experiments with anti-MAP2 (Fig. 10 c). The immunofluorescence signal was arranged in a dotted pattern along the dendrites, with the dots corresponding to synapses as demonstrated in double labeling experiments with anti-synaptophysin (Fig. 10 d).


Synaptopodin: an actin-associated protein in telencephalic dendrites and renal podocytes.

Mundel P, Heid HW, Mundel TM, Krüger M, Reiser J, Kriz W - J. Cell Biol. (1997)

Expression of synaptopodin in cultured hippocampal neurons. (a) In 25-d-old cultured hippocampal neurons, a dotted pattern of immunoreactivity in dendrites is seen, whereas axons (arrows) are not labeled. (b) Phase contrast microscopy. (c) Confocal laser  scanning double fluorescence analysis of synaptopodin (red) and MAP2 (green) to demonstrate the exclusive expression of synaptopodin in dendrites. (d) Confocal laser scanning double fluorescence analysis of synaptopodin and synaptophysin. The yellow signal results  from a complete overlap of the immunoreactivity and proves the synaptic localization of synaptopodin in cultured neurons. Bar, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2139823&req=5

Figure 10: Expression of synaptopodin in cultured hippocampal neurons. (a) In 25-d-old cultured hippocampal neurons, a dotted pattern of immunoreactivity in dendrites is seen, whereas axons (arrows) are not labeled. (b) Phase contrast microscopy. (c) Confocal laser scanning double fluorescence analysis of synaptopodin (red) and MAP2 (green) to demonstrate the exclusive expression of synaptopodin in dendrites. (d) Confocal laser scanning double fluorescence analysis of synaptopodin and synaptophysin. The yellow signal results from a complete overlap of the immunoreactivity and proves the synaptic localization of synaptopodin in cultured neurons. Bar, 10 μm.
Mentions: We next analyzed the expression of synaptopodin in cultured neurons derived from embryonic 18-d-old rat hippocampi. The expression started at day 12 in vitro, increased thereafter in parallel with process and spine formation, and reached its maximum expression after 25 d in vitro (Fig. 10 a). Like in vivo, synaptopodin was only found in dendrites as revealed in double labeling experiments with anti-MAP2 (Fig. 10 c). The immunofluorescence signal was arranged in a dotted pattern along the dendrites, with the dots corresponding to synapses as demonstrated in double labeling experiments with anti-synaptophysin (Fig. 10 d).

Bottom Line: In particular, synaptopodin does not contain functional domains found in receptor-clustering PSD proteins.The exclusive synaptopodin synthesis in the telencephalon has been confirmed by in situ hybridization, where synaptopodin mRNA is only found in perikarya of the olfactory bulb, cerebral cortex, striatum, and hippocampus, i.e., the expression is restricted to areas of high synaptic plasticity.From these results and experiments with cultured cells we conclude that synaptopodin represents a novel kind of proline-rich, actin-associated protein that may play a role in modulating actin-based shape and motility of dendritic spines and podocyte foot processes.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy and Cell Biology, University of Heidelberg, Germany. peter.mundel@urz.uni-heidelberg.de

ABSTRACT
Synaptopodin is an actin-associated protein of differentiated podocytes that also occurs as part of the actin cytoskeleton of postsynaptic densities (PSD) and associated dendritic spines in a subpopulation of exclusively telencephalic synapses. Amino acid sequences determined in purified rat kidney and forebrain synaptopodin and derived from human and mouse brain cDNA clones show no significant homology to any known protein. In particular, synaptopodin does not contain functional domains found in receptor-clustering PSD proteins. The open reading frame of synaptopodin encodes a polypeptide with a calculated Mr of 73.7 kD (human)/74.0 kD (mouse) and an isoelectric point of 9.38 (human)/9. 27 (mouse). Synaptopodin contains a high amount of proline ( approximately 20%) equally distributed along the protein, thus virtually excluding the formation of any globular domain. Sequence comparison between human and mouse synaptopodin revealed 84% identity at the protein level. In both brain and kidney, in vivo and in vitro, synaptopodin gene expression is differentiation dependent. During postnatal maturation of rat brain, synaptopodin is first detected by Western blot analysis at day 15 and reaches maximum expression in the adult animal. The exclusive synaptopodin synthesis in the telencephalon has been confirmed by in situ hybridization, where synaptopodin mRNA is only found in perikarya of the olfactory bulb, cerebral cortex, striatum, and hippocampus, i.e., the expression is restricted to areas of high synaptic plasticity. From these results and experiments with cultured cells we conclude that synaptopodin represents a novel kind of proline-rich, actin-associated protein that may play a role in modulating actin-based shape and motility of dendritic spines and podocyte foot processes.

Show MeSH