Subregion-specific p300 conditional knock-out mice exhibit long-term memory impairments

Abstract

Histone acetylation plays a critical role during long-term memory formation. Several studies have demonstrated that the histone acetyltransferase (HAT) CBP is required during long-term memory formation, but the involvement of other HAT proteins has not been extensively investigated. The HATs CBP and p300 have at least 400 described interacting proteins including transcription factors known to play a role in long-term memory formation. Thus, CBP and p300 constitute likely candidates for transcriptional coactivators in memory formation. In this study, we took a loss-of-function approach to evaluate the role of p300 in long-term memory formation. We used conditional knock-out mice in which the deletion of p300 is restricted to the postnatal phase and to subregions of the forebrain. We found that p300 is required for the formation of long-term recognition memory and long-term contextual fear memory in the CA1 area of the hippocampus and cortical areas.

Figure 1.

p300 conditional knock-out mice show reduced expression of p300 in the forebrain. (A) Immunohistochemical labeling of p300 in brain coronal sections from control and p300 conditional knock-out mice. (B) Western blot analysis of the levels of p300 in the cerebellum, hippocampus, and cortex of p300 conditional knock-out mice and control littermates (n = 5 per group); *P < 0.05. Picture shows a representative blot from hippocampal tissue. (C) Immunohistochemical labeling of CBP in brain coronal sections from control and p300 conditional knock-out mice. (D) Western blot analysis of CBP protein expression in the cerebellum, hippocampus, and cortex of p300 conditional knock-out mice and control littermates (n = 5 per group). Picture shows a representative blot from hippocampal tissue. Abbreviations: cKO, p300 conditional knock-out; Ct, control littermate; PRh, Perirhinal cortex; Ent, Entorhinal cortex; I, Insular cortex; CA1, CA1 area of the hippocampus; CA3, CA3 area of the hippocampus; DG, dentate gyrus area of the hippocampus; Amy, amygdala; Hipp, Hippocampus; Cb, Cerebelum; Cx, Cortex.

Figure 2.

Global histone acetylation levels in p300 conditional knock-out mice in CA1 and cortex. (A) Quantification of the global level of acetylation of histones H3 and H4 in the CA1 and perirhinal cortex of p300 conditional knock-out mice (n = 5) and control littermates (n = 7) assessed by immunohistochemistry. Reduced AcH3 is observed in caudal perirhinal cortex of p300 conditional knock-out mice; *P < 0.05. (B) Representative images of the rostral and caudal perirhinal cortex of p300 conditional knock-out mice and control littermates. Coronal brain sections were stained with an antibody against the acetylated form of histone H3. cKO, p300 conditional knock-out; Ct, control littermate; PRh, Perirhinal cortex; CA1, CA1 area of the hippocampus.

Figure 3.

p300 conditional knock-out mice show normal spontaneous activity, motor coordination, motor skill learning, and anxiety-related behavior. (A) p300 conditional knock-out mice (n = 5) and control littermates (n = 5) show similar distance traveled and velocity in an open field. (B) p300 conditional knock-out mice (n = 13) and control littermates (n = 13) show similar time on the rotarod across trials. (C) p300 conditional knock-out mice (n = 6) and control littermates (n = 6) spent similar time in the closed arms of the elevated zero-maze. cKO, p300 conditional knock-out; Ct, control littermate.

Figure 4.

p300 conditional knock-out mice show normal spatial memory when tested in the Morris water maze. (A) Control (n = 12) and p300 conditional knock-out (n = 12) mice do not show a significant difference in the latency to find the hidden platform during the acquisition phase of the task. (B) During the probe trial performed after session 8, p300 conditional knock-out mice and control littermates showed similar percentage of time spent swimming in the target quadrant. (C) During the probe trial performed after session 8, the number of crossings over the area where the platform was located during acquisition was not different between control and p300 conditional knock-out mice. cKO, p300 conditional knock-out; Ct, control littermate.

Figure 5.

p300 conditional knock-out mice show impaired long-term recognition memory. p300 conditional knock-out mice (n = 7) and control littermates (n = 7) show similar preference for the novel object when tested 30 min after training. However, when tested 24 h after training, p300 conditional knock-out mice (n = 6) show a significant lower preference for the novel object than their control littermates (n = 6); *P < 0.05. cKO, p300 conditional knock-out; Ct, control littermate.

Figure 6.

p300 conditional knock-out mice show impaired long-term contextual fear memory and normal cued fear memory. (A) p300 conditional knock-out mice (n = 10) show identical percentage of freezing compared to their control littermates (n = 10) when tested 1 h after training in the cued fear conditioning. (B) p300 conditional knock-out mice (n = 12) show a significant lower percentage of freezing compared to their control littermates (n = 12) when tested 24 h after training in the contextual fear conditioning; *P < 0.05. (C) p300 conditional knock-out mice (n = 8) show an identical percentage of freezing compared to their control littermates (n = 10) when tested 24 h after training in the cued fear conditioning. cKO, p300 conditional knock-out; Ct, control littermate.