S-Space College of Natural Sciences (자연과학대학) Dept. of Biological Sciences (생명과학부) Theses (Ph.D. / Sc.D._생명과학부)
Studies on the role of CCCTC-binding factor (CTCF) in remote memory and cortical synaptic plasticity
CTCF 단백질이 장기 기억과 대뇌피질 시냅스 가소성 조절에 미치는 영향에 대한 연구
- 자연과학대학 생명과학부
- Issue Date
- 서울대학교 대학원
- 학위논문 (박사)-- 서울대학교 대학원 : 자연과학대학 생명과학부, 2018. 2. 강봉균.
- The molecular mechanism of long-term memory has been extensively studied in the context of the hippocampus-dependent recent memory examined within several days. However, months-old remote memory maintained in the cortex for long-term has not been investigated much at the molecular level yet. Various epigenetic mechanisms are known to be important for long-term memory, but how the three-dimensional (3D) chromatin architecture and its regulator molecules contribute to neuronal plasticity and memory consolidation are still largely unknown. To assess memory upon the perturbation of the transcription and 3D chromatin structure, I chose the CCCTC-binding factor (CTCF), a seven-zinc finger protein well known for its role as a transcription factor and a chromatin regulator. I generated conditional knockout (cKO) mice, in which CTCF is lost in excitatory neurons during adulthood. The CTCF cKO mice showed normal recent memory in the contextual fear conditioning and spatial water maze tasks. However, they showed remarkable impairments in remote memory in both tasks. Underlying the remote memory-specific phenotypes, I observed that loss of CTCF disrupts cortical long-term potentiation (LTP), but not hippocampal LTP. Through RNA-sequencing, I observed that CTCF knockdown in cortical neuron culture caused altered expression of hundreds of genes. In the list of differentially expressed genes (DEGs), more number of genes were downregulated than upregulated. Also, through gene ontology (GO) enrichment analysis, I found that many DEGs are highly involved in functions such as cell adhesion, synaptic plasticity, and memory. For further investigation on the function of CTCF in the brain, I generated another cKO mouse line, in which CTCF was specifically deleted in inhibitory neurons. However, due to embryonic lethality, I used CTCF heterozygous (CTCF HT) instead of homozygous KO mice for experiments. In the behavioral experiments, I observed partial impairment of remote memory in the CTCF HT mice, which suggests that CTCF has a similar function of regulating remote memory in excitatory and inhibitory neurons. Moreover, as CTCF cKO mice have many number of genes with an abnormal expression level, I looked at CTCF cKO mice's brain to assess the long-term consequences of CTCF deletion. In the hippocampus and ACC of the aged CTCF cKO, I found strong signs of cell death and reactive gliosis, which are marks of neurodegeneration. Together, these results suggest that remote memory storage in the cortex requires CTCF-mediated transcription and chromatin regulation, while hippocampus-dependent short-term memory does not. Also, the results from aged CTCF cKO mice suggest that long-term CTCF deletion leads to neurodegeneration in two memory-related brain areas.