| Summary: | 碩士 === 國立陽明大學 === 神經科學研究所 === 105 === Peg10 (Paternally Expressed Gene 10) is expressed in early stages of mouse embryos. Peg10 is expressed in the mouse brain, but its detailed expression pattern and function in developing mouse brain are yet unkown. The main focus of my thesis was to study the expression pattern and function of Peg10 in developing mouse forebrain. In the first part of my thesis study, we investigated the expression pattern of Peg10 in developing mouse forebrain. Western blotting showed that Peg10-RF1 isoform, but not Peg10-RF1/2 isoform, was expressed in E13.5 developing mouse forebrain. In situ hybiridzation and immunostaining of Peg10 showed that Peg10 was expressed in the lateral ganglionic eminence (LGE, striatal primordia), medial ganglionic eminence, caudal ganglionic eminence, preoptic area, ventral thalamus and hypothalamus as early as E12.5. Peg10 was co-expressed with striatal markers of Nolz-1 and Islet-1 in E13.5. By E15.5, Peg10 was preferentially expressed at high levels in the primordium of nucleus accumbens (NAc) of ventral striatum. In contrast, Peg10 was expressed at low levels in the primordium of caudate-putamn (CP) of dorsal striatum. The NAc-seletive expression pattern of Peg10 in NAc continues postnatally. By postnatal day (P) 7 when the core and shell regions of NAc were distinguisable, Peg10 was predominatly expressed in the core with some Peg10-positive cells scattered in the shell. Moreover, Peg10 was co-expressed in subtance P-positive striatonigral and enkephalin-positive striatopallidal neurons in P7 and P14 NAc. In terms of neurogenesis, the birthdating analysis indicated that the number of Peg10;BrdUE15.5 cells were higher than Peg10;BrdUE12.5 cells in NAc, suggesting that Peg10-positive cells are born at later stages. The results of the expression pattern analyses suggest that Peg10-positive cell lineages contribute to the formation of the core region of NAc. For the second part of my thesis study, we attempted to indeifity the downstream traget genes of Peg10 and the neuobiological function of Peg10 in developing NAc. In utero electroporation of SH-Peg10 knockdon construct into E13.5 LGE resulted in an increase of Tuj1-positive differentaing neurons and a trend of decrease in proliferating Ki67-positive cells in E15.5 striatum, which suggests that Peg10 is required to maintain proliferation of neural progenitors in the LGE. We also identified Astn2 (astrotactin 2) as a potential target gene that was repressed by Peg10, because Peg10 knockdown up-regulated Astn2 expression in CP and NAc. Although previous study has shown involvement of Astn2 in neuronal migration in developing cerebellum, electroporation of SH-Peg10 knockdown and GFP reporter gene constructs into E13.5 LGE did not affect the distribution pattern of GFP-positive cells along the dorsal-ventral axis of E18.5 striatum, Nor did it affect the distribution pattern of GFP+ cells at E15.5 striatum, except that GFP+ cells were increased in the region of bin 4 in SH-Peg10 knockdown group compared to control group at level 2. Finally, based on transgenic over-expression of Nolz-1, we found reduction of Peg10 expression in NAc of Dlx6-cCre;Nolz-1 Tg brains, which was consistent with our previous finding of up-regulation of Nolz-1 in CP and NAc of Nolz-1 knockout brains. In summary, we have identified Peg10 as a NAc-enriched gene during development. An important question in striatal development is how dorsal and ventral striatum are parcellated during development. The biological signifcance of the Nolz-1-Peg10 and Peg10-Astn2 signaling pathways in developing CP and NAc with relevance to partition of dorsal and ventral striautm awaits furture studies.
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