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Back-signaling from CX3CL1 regulates neurogenesis during development and in the adult mouse

ABSTRACT: CX3CL1 was discovered as a chemokine, and is best known to function via interaction with its receptor CX3CR1. However, in this study, we report a unique role of CX3CL1 that is independent from this pathway. We show that CX3CL1 is naturally shedded by both α- and β-secretase. The membrane-anchored C-terminal fragment is further cleaved by γ-secretase to release the CX3CL1 intracellular domain (CX3CL1-ICD), which is translocated into the cell nucleus to control gene expression. Among the regulated genes, we noted prominent induction of TGFβ2/TGFβ3 signaling in cultured cells by CX3CL1-ICD. Mice overexpressing only the C-terminal fragment (Tg-CX3CL1-ct) strongly induced TGFβ3 expression, as evidenced by Western and RNAseq analyses. Phenotypically, Tg-CX3CL1-ct mice exhibited enhanced neurogenesis both during development and in adulthood. Enhanced adult neurogenesis was seen in both the subgranular zone and the subventricular zone. Together, we demonstrate that CX3CL1-ct has a back-signaling function by enhancing neurogenesis through TGFβ3 and other genes important for neurogenesis. Induction CX3CL1 back signaling may be a promising novel mechanism to replenish neuronal loss.

ORGANISM(S): Mus musculus

PROVIDER: GSE129722 | GEO | 2019/06/08

REPOSITORIES: GEO

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Project description:Background: In humans, cleft palate (CP) accounts for one of the largest number of birth defects with a complex genetic and environmental etiology. TGFβ3 has been established as an important regulator of palatal fusion in mice and it has been shown that TGFβ3-null mice exhibit CP without any other major deformities. However, the genes that regulate cellular decisions and molecular mechanisms maintained by the TGFβ3 pathway throughout palatogenesis are predominantly unexplored. Our objective in this study was to analyze global transcriptome changes within the palate during different gestational ages within TGFβ3 knockout mice to identify TGFβ3-associated genes previously unknown to be associated with the development of cleft palate. We used deep sequencing technology, RNA-Seq, to analyze the transcriptome of TGFβ3 knockout mice at crucial stages of palatogenesis, including palatal growth (E14.5), adhesion (E15.5), and fusion (E16.5). Results: The overall transcriptome analysis of TGFβ3 wildtype mice (C57BL/6) reveals that almost 6000 genes were upregulated during the transition from E14.5 to E15.5 and more than 2000 were downregulated from E15.5 to E16.5. Using bioinformatics tools and databases, we identified the most comprehensive list of CP genes (n = 322) in which mutations cause CP either in humans or mice, and analyzed their expression patterns. The expression motifs of CP genes between TGFβ3+/− and TGFβ3−/− were not significantly different from each other, and the expression of the majority of CP genes remained unchanged from E14.5 to E16.5. Using these patterns, we identified 8 unique genes within TGFβ3−/− mice (Chrng Foxc2, H19, Kcnj13, Lhx8, Meox2, Shh, and Six3), which may function as the primary contributors to the development of cleft palate in TGFβ3−/− mice. When the significantly altered CP genes were overlaid with TGFβ signaling, all of these genes followed the Smad-dependent pathway. Conclusions: Our study represents the first analysis of the palatal transcriptome of the mouse, as well as TGFβ3 knockout mice, using deep sequencing methods. In this study, we characterized the critical regulation of palatal transcripts that may play key regulatory roles through crucial stages of palatal development. We identified potential causative CP genes in a TGFβ3 knockout model, which may lead to a better understanding of the genetic mechanisms of palatogenesis and provide novel potential targets for gene therapy approaches to treat cleft palate.

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Back-signaling from CX3CL1 regulates neurogenesis during development and in the adult mouse

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