Regulation of TrkA and ChAT expression in developing rat basal forebrain: evidence that both exogenous and endogenous NGF regulate differentiation of cholinergic neurons

Abstract

TrkA is a receptor tyrosine kinase whose activation transduces NGF signaling. TrkA expression has been demonstrated in NGF-responsive adult basal forebrain cholinergic neurons (BFCNs). Several lines of evidence have suggested that endogenous NGF plays a role in the development and differentiation of these neurons. We examined TrkA expression during development. TrkA mRNA and protein were present in basal forebrain neurons during the entire postnatal period; the distribution of neurons bearing these markers was identical to that for those containing choline acetyltransferase (ChAT) mRNA, suggesting that, as in the adult, TrkA gene expression is localized to BFCNs. The expression of TrkA and ChAT followed a very similar temporal pattern, suggesting regulation by the same factor(s). We discovered that NGF administration in vivo activated TrkA receptors, and increased both TrkA and ChAT mRNA; conversely, anti-NGF infusions suppressed expression of both genes. These results suggest that endogenous NGF regulates expression of TrkA and ChAT. Finally, while NGF infusion increased the size of developing BFCNs, NGF antibodies inhibited the normal developmental increase. The results are evidence that endogenous NGF acts on developing BFCNs to enhance gene expression and cellular differentiation.

Bex3 Dimerization Regulates NGF-Dependent Neuronal Survival and Differentiation by EnhancingtrkAGene Transcription

“…To identify proteins that interact with the Trks, a yeast twohybrid screen was performed using a P0 rat DRG library and the juxtamembrane domain of TrkB receptor as a bait Lou et al, 2001;). Bex3 was identified once among the 75 positive clones obtained.…”

“…In vivo, a 457 bp sequence, highly conserved in mouse, chick, and human genes, upstream from the transcription start site seems to be required to drive coordinated trkA expression in sensory and sympathetic neurons (Ma et al, 2000;Lei and Parada, 2007). Several transcription factors have been reported to influence trkA gene expression, including Sp1, Brn3a, Klf7, and Runx1 (Huang et al, 1999;Sacristán et al, 1999;Lei et al, , 2005Ma et al, 2003;Marmigère et al, 2006;Lanier et al, 2007). It has been established that NGF treatment increases trkA mRNA levels in PC12 cells and cholinergic neurons (Miller et al, 1991;Holtzman et al, 1992;Li et al, 1995;, and HAND transcription factors partially regulate trkA expression in response to NGF in cultured sympathetic neurons without affecting the basal expression of trkA (i.e., in the absence of NGF; Doxakis et al, 2008).…”

Failed retrograde transport of NGF in a mouse model of Down's syndrome: Reversal of cholinergic neurodegenerative phenotypes following NGF infusion

“…NGF is a neurotrophic factor whose actions on BFCNs are required for their normal development and function (9). Given the marked similarities in the changes seen in the BFCNs of Ts65Dn mice and those in which animals have been deprived of NGF (10)(11)(12) or its receptors (13), we tested the hypothesis that the progressive abnormalities in BFCNs in Ts65Dn mice resulted from impaired NGF signaling. Our results suggest that deficient trophic support, because of failed retrograde transport of the NGF signal, contributes significantly to the neurodegenerative phenotype.…”

Basal forebrain cholinergic cell attachment and neurite outgrowth on organotypic slice cultures of hippocampal formation

“…However, it remains possible that the development of the cholinergic phenotype occurs preferentially in cells that have settled down in a supportive environment or have established appropriate adhesive contacts on the slice. Other studies have reported expression of the cholinergic phenotype in dissociated cultures (Dreyfus, 1989;Hartikka and Hefti, 1988;Li et al, 1995;Nonomura et al, 1996;Shingai et al, 1990), however, the presence of exogenously applied neurotrophic factors or the presence of normal target cells is important for expression of the cholinergic phenotype and for survival (Dreyfus, 1989;Ha et al, 1996;Hartikka and Hefti, 1988;Li et al, 1995;Morse et al, 1993;Nonomura et al, 1996;Shingai et al, 1990). Grown in isolation, without target contacts or supplemental neurotrophins, the BFCNs do not thrive.…”