Subcellular localization of patched and smoothened, the receptors for sonic hedgehog signaling, in the hippocampal neuron

Abstract

Cumulative evidence suggests that, aside from patterning the embryonic neural tube, Sonic hedgehog (Shh) signaling plays important roles in the mature nervous system. In this study, we investigate the expression and localization of the Shh signaling receptors, Patched (Ptch) and Smoothened (Smo), in the hippocampal neurons of young and mature rats. Reverse transcriptase-polymerase chain reaction and immunoblotting analyses show that the expression of Ptch and Smo remains at a moderate level in young postnatal and adult brains. By using immunofluorescence light microscopy and immunoelectron microscopy, we examine the spatial distribution of Ptch and Smo within the hippocampal neurons. In young developing neurons, Ptch and Smo are present in the processes and are clustered at their growth cones. In mature neurons, Ptch and Smo are concentrated in dendrites, spines, and postsynaptic sites. Synaptic Ptch and Smo often co-exist with unusual structures—synaptic spinules and autophagosomes. Our results reveal the anatomical organization of the Shh receptors within both the young and the mature hippocampal neurons.

Sonic hedgehog regulates presynaptic terminal size, ultrastructure and function in hippocampal neurons

“…Our conclusion about the importance of Shh activity for regulating synapse development is fully consistent with that of Harwell et al, and the similar results obtained with different types of neurons using very different experimental approaches makes the conclusion even more meaningful and physiologically relevant. It is worth noting that the findings by Harwell et al also support our previous observations of the dendritic source of Shh (Petralia et al, 2011b) in hippocampal neurons and the negligible Ptch and Smo on the axons (Petralia et al, 2011a;Petralia et al, 2012).…”

“…In the central nervous system, the best-characterized function for Shh is its ability to stimulate the proliferation of cerebellar granule cells (Dahmane and Ruiz i Altaba, 1999;Wallace, 1999;Wechsler-Reya and Scott, 1999) and neural progenitor cells residing in specific areas of the brain (Lai et al, 2003;Palma et al, 2005;Breunig et al, 2008;Han et al, 2008). In addition to acting as a mitogen for cells with stem-cell properties, Shh signaling components remain expressed in differentiated (postmitotic) neurons, including hippocampal neurons (Traiffort et al, 1999;Sasaki et al, 2010;Petralia et al, 2011a;Petralia et al, 2011b). In this study, we investigated whether Shh signaling activity has a function in hippocampal neurons.…”

Structure, Distribution, and Function of Neuronal/Synaptic Spinules and Related Invaginating Projections

“…Similarly, in the mossy terminals of the rat hippocampus, numerous spinules form from the convoluted postsynaptic dendrite protrusions (“thorny excrescences”; Chicurel and Harris 1992; Petralia et al 2011; Fig. 7).…”

“…Purkinje cell spines that form synapses with climbing fibers also sometimes may invaginate almost completely into the climbing fiber terminal (Palay and Chan-Palay 1974). In the giant mossy fiber terminals of the hippocampus (see “Small Postsynaptic Invaginating Projections: Spinules” section), the postsynaptic thorny excrescences, although not technically spines, can be nearly completely invaginated into the mossy terminals (Nitsch and Rinne 1981; Chicurel and Harris 1992; Petralia and Wenthold 1992; Petralia et al 2011). Inner hair cells of the mouse cochlea (see subsequent sections below) can be involved in a three-way circuit among a hair cell body, and afferent and efferent terminals, and all three processes may include some invaginating postsynaptic spine processes (Sobkowicz et al 2003).…”

“…Also, there are many more perforated PSDs and spinules after training; many of these spinules form a connection between two thorns. Petralia et al (2011) found that the spinule structures in the mossy terminals were labeled abundantly with immunogold for the sonic hedgehog (Shh) receptors, patched and smoothened (Fig. 7).…”