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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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Western blot analysis of synaptopodin with  mAb G1. Lanes 1–4 show the  immunodetection; lanes 1′–4′  show staining of the identical  membrane with Coomassie  brilliant blue to demonstrate  protein loading and separation. Cytosolic extracts from  rat forebrain (lane 1), cerebellum (lane 2), and isolated glomeruli (lanes 3 and 4) were analyzed in parallel. While in the forebrain a protein of ∼100 kD is  present, no protein expression is seen in cerebellum. In kidney a  110-kD band is observed. The extract in lane 4 had been kept at  4°C for 24 h before separation. Several proteolytic fragments appear; the band indicated by an arrowhead represents the originally described 44-kD protein.
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Figure 1: Western blot analysis of synaptopodin with mAb G1. Lanes 1–4 show the immunodetection; lanes 1′–4′ show staining of the identical membrane with Coomassie brilliant blue to demonstrate protein loading and separation. Cytosolic extracts from rat forebrain (lane 1), cerebellum (lane 2), and isolated glomeruli (lanes 3 and 4) were analyzed in parallel. While in the forebrain a protein of ∼100 kD is present, no protein expression is seen in cerebellum. In kidney a 110-kD band is observed. The extract in lane 4 had been kept at 4°C for 24 h before separation. Several proteolytic fragments appear; the band indicated by an arrowhead represents the originally described 44-kD protein.

Mentions: Using mAb G1, a heat-stable protein with an apparent molecular mass of 100 kD was recognized by immunoblotting in cytosolic extracts from rat brain (Fig. 1). In cytosolic fractions from isolated rat kidney glomeruli, a heat-stable band with an apparent molecular mass of 110 kD was shown (Fig. 1). The originally described 44-kD band (Mundel et al., 1991) represents a proteolytic fragment of the 110-kD protein (Fig. 1). On two-dimensional gel electrophoresis, synaptopodin appeared as a very basic protein with an isoelectric point around 9.4 (Fig. 2).


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)

Western blot analysis of synaptopodin with  mAb G1. Lanes 1–4 show the  immunodetection; lanes 1′–4′  show staining of the identical  membrane with Coomassie  brilliant blue to demonstrate  protein loading and separation. Cytosolic extracts from  rat forebrain (lane 1), cerebellum (lane 2), and isolated glomeruli (lanes 3 and 4) were analyzed in parallel. While in the forebrain a protein of ∼100 kD is  present, no protein expression is seen in cerebellum. In kidney a  110-kD band is observed. The extract in lane 4 had been kept at  4°C for 24 h before separation. Several proteolytic fragments appear; the band indicated by an arrowhead represents the originally described 44-kD protein.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 1: Western blot analysis of synaptopodin with mAb G1. Lanes 1–4 show the immunodetection; lanes 1′–4′ show staining of the identical membrane with Coomassie brilliant blue to demonstrate protein loading and separation. Cytosolic extracts from rat forebrain (lane 1), cerebellum (lane 2), and isolated glomeruli (lanes 3 and 4) were analyzed in parallel. While in the forebrain a protein of ∼100 kD is present, no protein expression is seen in cerebellum. In kidney a 110-kD band is observed. The extract in lane 4 had been kept at 4°C for 24 h before separation. Several proteolytic fragments appear; the band indicated by an arrowhead represents the originally described 44-kD protein.
Mentions: Using mAb G1, a heat-stable protein with an apparent molecular mass of 100 kD was recognized by immunoblotting in cytosolic extracts from rat brain (Fig. 1). In cytosolic fractions from isolated rat kidney glomeruli, a heat-stable band with an apparent molecular mass of 110 kD was shown (Fig. 1). The originally described 44-kD band (Mundel et al., 1991) represents a proteolytic fragment of the 110-kD protein (Fig. 1). On two-dimensional gel electrophoresis, synaptopodin appeared as a very basic protein with an isoelectric point around 9.4 (Fig. 2).

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
Related in: MedlinePlus