Synaptic protein and pan-neuronal gene expression and their regulation by Dicer-dependent mechanisms differ between neurons and neuroendocrine cells

Abstract

BackgroundNeurons in sympathetic ganglia and neuroendocrine cells in the adrenal medulla share not only their embryonic origin from sympathoadrenal precursors in the neural crest but also a range of functional features. These include the capacity for noradrenaline biosynthesis, vesicular storage and regulated release. Yet the regulation of neuronal properties in early neuroendocrine differentiation is a matter of debate and the developmental expression of the vesicle fusion machinery, which includes components found in both neurons and neuroendocrine cells, is not resolved.ResultsAnalysis of synaptic protein and pan-neuronal marker mRNA expression during mouse development uncovers profound differences between sympathetic neurons and adrenal chromaffin cells, which result in qualitatively similar but quantitatively divergent transcript profiles. In sympathetic neurons embryonic upregulation of synaptic protein mRNA follows early and persistent induction of pan-neuronal marker transcripts. In adrenal chromaffin cells pan-neuronal marker expression occurs only transiently and synaptic protein messages remain at distinctly low levels throughout embryogenesis. Embryonic induction of synaptotagmin I (Syt1) in sympathetic ganglia and postnatal upregulation of synaptotagmin VII (Syt7) in adrenal medulla results in a cell type-specific difference in isoform prevalence. Dicer 1 inactivation in catecholaminergic cells reduces high neuronal synaptic protein mRNA levels but not their neuroendocrine low level expression. Pan-neuronal marker mRNAs are induced in chromaffin cells to yield a more neuron-like transcript pattern, while ultrastructure is not altered.ConclusionsOur study demonstrates that remarkably different gene regulatory programs govern the expression of synaptic proteins in the neuronal and neuroendocrine branch of the sympathoadrenal system. They result in overlapping but quantitatively divergent transcript profiles. Dicer 1-dependent regulation is required to establish high neuronal mRNA levels for synaptic proteins and to maintain repression of neurofilament messages in neuroendocrine cells.

MiR-124 is differentially expressed in derivatives of the sympathoadrenal cell lineage and promotes neurite elongation in chromaffin cells

“…MiR-124 was present in sympathetic ganglia but was completely undetectable in adrenal glands. In confirmation of the profiling results, we have previously shown that miR-124 can be detected by in situ hybridization in developing mouse sympathetic ganglia at E16.5 (Stubbusch et al 2013). Here, we .…”

“…The loss of the microRNA-processing enzyme dicer has been shown to severely reduce the survival of sympathetic neuron precursors (Huang et al 2010;Zehir et al 2010) and also partially to affect the establishment of their typical neuronal gene expression pattern (Stubbusch et al 2013). Notably, sympathetic neurons of dicer-deficient mouse embryos exhibit reduced expression levels of synaptic marker genes and thus become more reminiscent of wildtype chromaffin cells in this respect.…”

“…In situ hybridization and preparation of digoxigenin-labelled probes for mouse DBH (Tiveron et al 1996) and mouse steroidogenic factor 1 (SF-1; Gut et al 2005) were performed on 10-μm-thick cryosections as described previously (Ernsberger et al 1997). MiR-124 in situ hybridization was carried out on 10-μm-thick cryosections as described previously (Stubbusch et al 2013) by using a 5′ digoxigenin-labelled RNA modified probe for miR124 (88066-01 Exiqon, Vedbaek, Denmark) and scrambled control (99004-01, Exiqon).…”

“…We have shown recently that the microRNA-producing enzyme dicer plays an important role in the development of both sympathetic neurons and chromaffin cells by affecting their survival and contributing to the establishment of their respective specific gene expression pattern (Stubbusch et al 2013). In particular, dicer inactivation compromises transcript accumulation for synaptic proteins in sympathetic neurons and repression of neurofilaments in chromaffin cells, features characteristic for neuronal and endocrine cells, respectively.…”

Immunocytochemical markers of neuronal maturation in human diagnostic neuropathology

“…Various gene regulatory programmes govern the expression of synaptic proteins in the neuronal and neuroendocrine branches of the sympatho-adrenal system; Dicer-1-dependent regulation facilitates the establishment of high neuronal mRNA levels for synaptic proteins and represses neurofilament messages in neuroendocrine cells so that neurites do not form (Stubbusch et al 2013).…”