Expression of gamma secretase and notch signalling pathway in TS1CJE mouse model of down syndrome
Many medical complications such as hypotonia, congenital heart defects, intellectual disability and cognitive impairments are seen in Down syndrome (DS) individuals. Studies have shown that an increased glial-to-neuron ratio contributes to the intellectual disability of DS individuals. This neuro...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English |
| Published: |
2017
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/90075/3/FPSK%28M%29%202019%2036%20%20UPM%20ir.pdf |
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| Summary: | Many medical complications such as hypotonia, congenital heart defects, intellectual
disability and cognitive impairments are seen in Down syndrome (DS) individuals.
Studies have shown that an increased glial-to-neuron ratio contributes to the intellectual
disability of DS individuals. This neurogenic-to-gliogenic shift is characterised by an
increased preference of neural progenitor cells committing to glial cell fate. To further
understand the underlying mechanism of the shift, we utilised a mouse model for DS
known as Ts1Cje that possesses a partial triplication of the mouse chromosome 16
(MMU16) that is syntenic to human chromosome 21 (HSA21). Ts1Cje have shown to
have similar off balance cellular ratio in the brain. Notch signalling pathway is involved
in the regulation of the proliferation of NPCs and inhibit neuronal cell commitment and
promote glial cell fate. Notch protein is cleaved by gamma-secretase, a multi subunit
transmembrane protein complex that releases the Notch intracellular domain (NICD)
activating the downstream targets. The dysregulation of the gamma-secretase complex
(Psen1, Ncstn, Aph-1b, Psenen) and Notch (Notch1 and Notch2) could lead to the
imbalances seen in the brain of DS individuals. This study aims to profile the
spatiotemporal gene expression of gamma-secretase and Notch signalling components
during prenatal and postnatal timepoints in Ts1Cje mice. Gene expression analysis using
RT-qPCR was done on embryonic brain samples (E10.5, E15.5, P1.5) and postnatal
brain from three regions (cerebellum, cerebral cortex, and hippocampus) at four
timepoints (P1, P15, P30, and P84). Results demonstrated inconclusive alterations in
gene expression between Ts1Cje and wildtype mice due to the cellular heterogeneity of
the samples. Results from RT-qPCR analysis from E15.5 neurosphere culture showed
an increase of expression of Psen1, and Aph-1b genes instead of Notch signalling genes
suggesting a potential dysregulation of gamma secretase regulated Notch-signalling
pathway during early NPCs fate determination and differentiation. The western blot
analysis of notch intracellular domain (NICD) however reveals decreased in Notch
activation in Ts1Cje suggesting abnormal proteolytic processing of Notch prior to gamma-secretase cleavage. This data is supported by increased gamma-secretase activity
using AlphaLISA assay in Ts1Cje embryonic neurosphere culture using artificial
recombinant Notch substrate. This study suggests the potential role of Notch signalling
and gamma-secretase in neurogenic-to-gliogenic shift through abnormal maintenance
and proliferation of NSCs pool. |
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