Postnatal development of synaptopodin expression in the rodent hippocampus

Abstract

Synaptopodin is an actin-binding protein of renal podocytes and dendritic spines. We have recently shown that synaptopodin is localized to the spine apparatus, a characteristic organelle of dendritic spines on forebrain neurons. Synaptopodin-deficient mice do not form spine apparatuses, indicating a role of synaptopodin in the formation of this organelle. Here we studied the development of synaptopodin expression in the postnatal rat hippocampus. At birth, synaptopodin mRNA is mainly expressed in CA3 pyramidal neurons. At postnatal day (P) 6, synaptopodin mRNA expression is still strongest in CA3 but is now also found in CA1 pyramidal neurons and granule cells of the suprapyramidal blade of the dentate gyrus. At P9, an almost adult pattern is seen with synaptopodin mRNA expressed by virtually all principal neurons. While synaptopodin mRNA was restricted to cell somata, immunostaining for synaptopodin protein labeled dendritic layers. At birth, no immunoreactivity was visible, while at P5 a weak staining mainly in stratum oriens was observed. At P9, immunolabeling was still strongest in stratum oriens followed by the molecular layer of the dentate gyrus. The adult pattern with strong labeling of all dendritic layers was reached by P12. Together these findings show that synaptopodin expression follows the well-known sequence of hippocampal principal neuron development. Unexpectedly, we also observed synaptopodin mRNA expression in a small population of interneurons as revealed by double labeling with interneuron markers. However, no immunolabeling for synaptopodin was observed in identified interneurons, confirming that the protein is mainly present in spine-bearing principal cells.

3D‐reconstruction and functional properties of GFP‐positive and GFP‐negative granule cells in the fascia dentata of the Thy1‐GFP mouse

“…In some cases, individual mossy fiber axons could be traced from the soma through the hilus into stratum lucidum of CA3 where they formed boutons and terminated on putative CA3 pyramidal cells (data not shown). In addition, GFP-positive hilar mossy cells were observed, as has been reported previously (Czarnecki et al, 2005). The axons of these cells terminate in the IML where they form a GFP-positive commissural/associational fiber plexus.…”

“…The inner molecular layer (IML) could be readily identified in our tissue sections because many commissural/associational fibers are GFP-positive in the Thy1-GFP mouse (Czarnecki et al, 2005). The outer molecular layer (OML) was defined as the portion of the molecular layer located between the IML and the hippocampal fissure.…”

Krüppel-Like Factor 9 Is Necessary for Late-Phase Neuronal Maturation in the Developing Dentate Gyrus and during Adult Hippocampal Neurogenesis

“…2, available at www.jneurosci.org as supplemental material). The remarkable similarity between the expression pattern of Klf-9 with that of synaptic proteins such as synaptopodin in the developing DG (Czarnecki et al, 2005) suggests a role for Klf-9 in regulating late-phase neuronal maturation. Together, these results suggest that Klf-9 expression defines a novel window of terminal differentiation that is characterized by high NeuroD2 expression, presence of calbindin immunoreactivity, and absence of calretinin immunoreactivity (Fig.…”

Synaptopodin Regulates Plasticity of Dendritic Spines in Hippocampal Neurons

“…Assuming that SP is found in mature and functional synapses (Mundel et al, 1997;Czarnecki et al, 2005), we examined whether SP(ϩ) spines are more likely to be associated with a synaptophysin-positive presynaptic terminal than SP(Ϫ) spines. The results are shown in Figure 1 E-H.…”