| Summary: | 博士 === 國立臺灣大學 === 微生物學研究所 === 105 === Part I:
Breast carcinoma amplified sequence 2 (BCAS2) is a 26 kDa nuclear protein.Recent studies demonstrated that there were at least two BCAS2 mechanisms involved in carcinogenesis: (1) BCAS2 is a negative regulator of p53: Deprivation of BCAS2 causes apoptosis in p53 wild-type cell lines but leads G2/M arrest in p53 null and p53 mutant cell lines; (2) binding to a single-stranded DNA-binding protein associated with the DNA repair function of the hPrp19 complex, which involves in the DNA damage response. In addition, BCAS2 is a core component of the hPrP19 complex that controls RNA splicing. Our previous studies revealed that wing-specific knockdown of BCAS2 leads to Drosophila wing developmental defects, which result from the participation of BCAS2 in Delta pre-mRNA splicing and regulation of Delta-Notch signaling. Here, we performed an exon array assay and showed that β-catenin is a target of BCAS2 splicing regulation. The regulation of dendrite growth and morphology by β-catenin is well documented. Therefore, we generated conditional knockout (cKO) mice to eliminate the BCAS2 expression in the forebrain to investigate the role of BCAS2 in dendrite growth. BCAS2 cKO mice showed a microcephaly-like phenotype with a reduced volume in the dentate gyrus (DG) and low levels of learning and memory, as evaluated using Morris water maze analysis and passive avoidance, respectively. Golgi staining revealed shorter dendrites, less dendritic complexity and decreased spine density in the DG of BCAS2 cKO mice. Moreover, the cKO mice displayed a short dendrite length in newborn neurons labeled by DCX, a marker of immature neurons, and BrdU incorporation. To further examine the mechanism underlying BCAS2-mediated dendritic malformation, we overexpressed β-catenin in BCAS2-depleted primary neurons and found that the dendritic growth was restored. In summary, BCAS2 is an upstream regulator of β-catenin gene expression and plays a role in dendrite growth at least partly through β-catenin.
Part II:
Previously we characterized that BCAS2 is an upstream regulator for β-catenin gene splicing; and plays a role in dendritic growth at least partly through β-catenin using conditional depletion of BCAS2 in the forebrain (named BCAS2 cKO). BCAS2 cKO mice show a reduction of dentate gyrus (DG) volume. To extensively characterize the volume of cortex in BCAS2 cKO that were driven by CaMKII-Cre, we found that depletion of BCAS2 could cause a reduction ratio of forebrain weight to body weight in comparison to WT; suggesting a microcephaly phenotype. IFA analysis of BCAS2 cKO revealed that BCAS2 expression was not only diminished in DG but also in other forebrain regions including cortex, striatum, thalamus and hypothalamus. The deprivation of BCAS2 caused the reduction of somatosensory cortical thickness (chosen from a range of bregma -1.45 mm to -1.68 mm) and pyramidal neuronal size in layer V. However the pyramidal neuron number was comparable in comparison to wt, however the density of neuron was higher in cKO than control. Taken together, BCAS2 cKO mice exhibit the reduced cortex volume.
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