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Relationship: 2732
Title
Decrease, SHH second messenger production leads to Decrease, Cell proliferation
Upstream event
Downstream event
Key Event Relationship Overview
AOPs Referencing Relationship
AOP Name | Adjacency | Weight of Evidence | Quantitative Understanding | Point of Contact | Author Status | OECD Status |
---|---|---|---|---|---|---|
Antagonism of Smoothened receptor leading to orofacial clefting | adjacent | Low | Low | Arthur Author (send email) | Under development: Not open for comment. Do not cite | Under Development |
Decrease, GLI1/2 target gene expression leads to orofacial clefting | adjacent | Low | Low | Agnes Aggy (send email) | Under development: Not open for comment. Do not cite | Under Development |
Taxonomic Applicability
Sex Applicability
Sex | Evidence |
---|---|
Unspecific |
Life Stage Applicability
Term | Evidence |
---|---|
Embryo | High |
Key Event Relationship Description
SHH is a mitogen that regulates cell proliferation during development. SHH regulation of proliferation works at least in part through regulation of cyclin D1 (ccnd 1) and cyclin D2 (Ccnd 2) (Kenney and Rowitch 2000, Ishibashi and McMahon 2002, Lobjois, Benazeraf et al. 2004, Mill, Mo et al. 2005, Hu, Mo et al. 2006). The regulation of ccnd 1 and ccnd 2 by SHH is not fully understood but is believed to be in part by regulation via SHH signaling and its signaling to SHH secondary messengers, namely the fibroblast growth factor family and GLI. GLI1 has been shown to directly bind and regulate ccnd1 and ccnd2 (Yoon, Kita et al. 2002). A network of reciprocal growth factor signaling between the epithelium and mesenchyme is required for proper growth and patterning of the early palatal shelves. This signaling is largely comprised of a network between bone morphogenic protein (BMP), Fibroblast growth factor (Fgf), and Sonic Hedgehog (SHH) (Zhang, Song et al. 2002, Rice, Spencer-Dene et al. 2004). Activation of the SHH pathway results in a downstream signaling cascade resulting in the relocation of GLI to the nucleus and subsequent gene transcription (Carballo, Honorato et al. 2018). This gene expression drives secondary messenger signaling for the pathway. Proper Msx1 activity in the mesenchyme is required for the expression of SHH in the overlying epithelium (Zhang, Song et al. 2002). Maintenance of SHH expression in the epithelium is believed to be dependent on Fgf10 expression in the mesenchyme and its’ signaling through Fgfr2b in the epithelium (Rice, Spencer-Dene et al. 2004).
Evidence Collection Strategy
Pubmed was used as the primary database for evidence collection. Searches are organized by the date and search terms used in the supplementary table. Search results were initially screened through review of the title and abstract for potential for data relating SHH signaling and secondary messengers and SHH cellular proliferation. Each selected publication and its’ data were then examined to determine if support or lack thereof existed for this KER. Papers that did not show any data relating to this KER were discarded. The search terms used are organized below in Table 1.
Evidence Supporting this KER
Biological Plausibility
The SHH pathway is well known to be associated with cellular proliferation. There is a high biological probability that this proliferation results through regulation of SHH secondary messengers.
Empirical Evidence
- In vitro
- Mouse cerebellar granule cells exposed to cycloheximide and SHH did not promote upregulation of ccnd 1, ccnd 2, or ccn3 mRNA. This supports that there is a protein intermediate between the SHH pathway and regulation of the G1 cyclins(Kenney and Rowitch 2000).
- In vivo
- In mouse palate explants application of SHH was found to induce proliferation in the palatal mesenchyme as measured by BrdU (Rice, Spencer-Dene et al. 2004).
- In CD-1 WT and MSX-1-/-, SHH soaked beads were able to induce proliferation in palatal mesenchyme explants at 24hr but not after 8hr suggesting the induction of proliferation is through an indirect mechanism (Zhang, Song et al. 2002).
- IHC staining for Ccnd-1 and Ccnd-2 in Osr2-IresCre Smoc/c (SHH inactive) and control embryos was used to determine if expression patterns differed between the mesenchyme and epithelium in mutants. Expression for both Ccnd-1 and Ccnd-2 was found to be reduced in the mesenchyme for mutants. mRNA was found to be reduced for both Ccnd-1 and Ccnd-2 in the palatal mesenchyme (Lan and Jiang 2009).
- In Osr2-IresCre;Smoc/c (SHH pathway inactive) mutant mice Fgf10 mRNA was found to be significantly reduced in the anterior palatal mesenchyme. The expression of Fgf10 correlated with a downregulation of PTCH1 (Lan and Jiang 2009).
- To determine if SHH can induce Fgf10, SHH overexpressing cells were implanted in the anterior region of the wing bud of chick embryos. By 27 hours, the expression of Fgf10 had significantly increased and expanded from the anterior mesenchyme to the bifurcating wing bud (Ohuchi, Nakagawa et al. 1997).
- To investigate whether MSX-1 is in the same pathway as Fgf10, MSX-1 expression was examined in Fgf10-/- mice and Fgf10 expression was examined in Msx-1-/- mice. No change in expression was found and it is concluded that MSX-1 is not a downstream target of Fgf10 (Alappat, Zhang et al. 2005).
- SHH expression is reduced in the palatal epithelium of both Fgf10-/- and Fgfr2b -/- mutants. Exogenous Fgf10 induced SHH in WT palatal epithelium (Rice, Spencer-Dene et al. 2004).
- Fgf8 activity was found to sustain ccnd 2 expression in the neural groove and that the attenuation of fgf signalling is necessary for the up regulation of ccnd 1. This was conducted using chick embryos and replacing a small piece of the rostral presomitic mesoderm with an Fgf8 soaked bead. To test the necessity of the Fgf pathway, SU5402 treatment was used (Lobjois, Benazeraf et al. 2004).
- Cyclopamine treatment of stage 9-10 chick embryos in the neural tube and neural grove resulted in a strong down regulation of ccnd 1 transcripts as well as SHH target genes (e.g. Gli1). Toxicity was assessed using sox2 and effects due to non-specific toxicity were not found. Ccnd 2 expression was not affected by cyclopamine treatment. This suggests that the iniation of ccnd 1 in the neural groove is SHH dependent while ccnd 2 is not (Lobjois, Benazeraf et al. 2004).
- Decreased proliferation correlating with downregulation of GLI1 and PTCH1 was found in E10.25 mouse embryos treated with cyclopamine (Everson, Fink et al. 2017).
Uncertainties and Inconsistencies
The relationship between a decrease is SHH secondary messenger production and a decrease in cellular proliferation is plausible and data is shown that supports a decrease in ccnd 1 and 2 in correlation with the Fgf and SHH pathways. Further studies are needed to further out understanding of the regulation of proliferation by SHH.
Known modulating factors
Quantitative Understanding of the Linkage
The quantitative understanding of this relationship is low. No studies were found to exist to address dose response or time-scale data. Further work is needed to address these questions and create a better understanding of this relationship.
Response-response Relationship
Time-scale
Known Feedforward/Feedback loops influencing this KER
Domain of Applicability
The relationship between a decrease in SHH secondary messengers and a decrease in cellular proliferation translocation has been demonstrated in both mouse and chick models. The relationship is biologically plausible in human, but to date no specific experiments have addressed this question. The SHH pathway is well understood to be fundamental to proper embryonic development and that aberrant SHH signaling during embryonic development can cause birth defects including orofacial clefts (OFCs). For this reason, this KER is applicable to the embryonic stage with a high level of confidence.
References
Alappat, S. R., Z. Zhang, K. Suzuki, X. Zhang, H. Liu, R. Jiang, G. Yamada and Y. Chen (2005). "The cellular and molecular etiology of the cleft secondary palate in Fgf10 mutant mice." Dev Biol 277(1): 102-113.
Carballo, G. B., J. R. Honorato, G. P. F. de Lopes and T. C. L. d. S. e. Spohr (2018). "A highlight on Sonic hedgehog pathway." Cell Communication and Signaling 16(1): 11.
Everson, J. L., D. M. Fink, J. W. Yoon, E. J. Leslie, H. W. Kietzman, L. J. Ansen-Wilson, H. M. Chung, D. O. Walterhouse, M. L. Marazita and R. J. Lipinski (2017). "Sonic hedgehog regulation of Foxf2 promotes cranial neural crest mesenchyme proliferation and is disrupted in cleft lip morphogenesis." Development 144(11): 2082-2091.
Hu, M. C., R. Mo, S. Bhella, C. W. Wilson, P. T. Chuang, C. C. Hui and N. D. Rosenblum (2006). "GLI3-dependent transcriptional repression of Gli1, Gli2 and kidney patterning genes disrupts renal morphogenesis." Development 133(3): 569-578.
Ishibashi, M. and A. P. McMahon (2002). "A sonic hedgehog-dependent signaling relay regulates growth of diencephalic and mesencephalic primordia in the early mouse embryo." Development 129(20): 4807-4819.
Kenney, A. M. and D. H. Rowitch (2000). "Sonic hedgehog promotes G(1) cyclin expression and sustained cell cycle progression in mammalian neuronal precursors." Mol Cell Biol 20(23): 9055-9067.
Lan, Y. and R. Jiang (2009). "Sonic hedgehog signaling regulates reciprocal epithelial-mesenchymal interactions controlling palatal outgrowth." Development 136(8): 1387-1396.
Lobjois, V., B. Benazeraf, N. Bertrand, F. Medevielle and F. Pituello (2004). "Specific regulation of cyclins D1 and D2 by FGF and Shh signaling coordinates cell cycle progression, patterning, and differentiation during early steps of spinal cord development." Dev Biol 273(2): 195-209.
Mill, P., R. Mo, M. C. Hu, L. Dagnino, N. D. Rosenblum and C. C. Hui (2005). "Shh controls epithelial proliferation via independent pathways that converge on N-Myc." Dev Cell 9(2): 293-303.
Ohuchi, H., T. Nakagawa, A. Yamamoto, A. Araga, T. Ohata, Y. Ishimaru, H. Yoshioka, T. Kuwana, T. Nohno, M. Yamasaki, N. Itoh and S. Noji (1997). "The mesenchymal factor, FGF10, initiates and maintains the outgrowth of the chick limb bud through interaction with FGF8, an apical ectodermal factor." Development 124(11): 2235-2244.
Rice, R., B. Spencer-Dene, E. C. Connor, A. Gritli-Linde, A. P. McMahon, C. Dickson, I. Thesleff and D. P. Rice (2004). "Disruption of Fgf10/Fgfr2b-coordinated epithelial-mesenchymal interactions causes cleft palate." J Clin Invest 113(12): 1692-1700.
Yoon, J. W., Y. Kita, D. J. Frank, R. R. Majewski, B. A. Konicek, M. A. Nobrega, H. Jacob, D. Walterhouse and P. Iannaccone (2002). "Gene expression profiling leads to identification of GLI1-binding elements in target genes and a role for multiple downstream pathways in GLI1-induced cell transformation." J Biol Chem 277(7): 5548-5555.
Zhang, Z., Y. Song, X. Zhao, X. Zhang, C. Fermin and Y. Chen (2002). "Rescue of cleft palate in Msx1-deficient mice by transgenic Bmp4 reveals a network of BMP and Shh signaling in the regulation of mammalian palatogenesis." Development 129(17): 4135-4146.