Impaired learning and motor behavior in heterozygous Pafah1b1 (Lis1) mutant mice

Abstract

Heterozygous mutation or deletion of Pafab1b1 (LIS1) in humans is associated with syndromes with type 1 lissencephaly, a severe brain developmental disorder resulting from abnormal neuronal migration. We have created Lis1 heterozygous mutant mice by gene targeting. Heterozygous mutant mice are viable and fertile, but display global organizational brain defects as a result of impaired neuronal migration. To assess the functional impact of the mutation, Lis1 heterozygous mice and their wild-type littermates were evaluated on a wide variety of behavioral tests. Lis1 mutant mice displayed abnormal hindpaw clutching responses and were impaired on a rotarod test. Lis1 heterozygous mice were also impaired in the spatial learning version of the Morris water task. Impaired motor behavior and spatial learning and memory in Lis1 mutant mice indicates that impaired neuronal migration can have functional effects on complex behavioral responses. The behavioral findings also support the use of the Lis1 mutant mice as a model from human type 1 lissencephaly.

Figure 1

Horizontal activity (A), vertical activity (B), and the center distance-to-total distance ratio (C) for Lis1 heterozygous (○, +/−) mutant and wild-type (●, +/+) mice during the 30-min open field test. There were no significant differences between +/− and +/+ mice on any of the open field measurements (P > 0.1). Data are represented as the mean (±s.e.m.)

Figure 2

Time spent balanced on top of the rotating rod across three test trials for Lis1 heterozygous (○, +/−) mutant and wild-type (●, +/+) mice. Overall significant difference between Lis1 heterozygous (+/−) mutant and wild-type (+/+) mice, P < 0.000001. There were no significant differences (P > 0.5) between mice that used active- or passive-performing response strategies (see text). Data are represented as the mean (±s.e.m.).

Figure 3

Startle amplitude to the 120-dB stimulus (A), and levels (%) of prepulse inhibition of the acoustic startle response (B) for Lis1 heterozygous (□, +/−) mutant and wild-type (█, +/+) mice. There were no significant differences between +/− and +/+ mice for the acoustic startle response (P > 0.3) or prepulse inhibition (P > 0.7). Data are represented as the mean (±s.e.m.).

Figure 4

Latency to find the hidden platform in the Morris water task for Lis1 heterozygous (○, +/−) mutant and wild-type (●, +/+) mice. There were no significant differences between +/− and +/+ mice (P > 0.3). Data are represented as the mean (±s.e.m.).

Figure 5

Probe trial data after hidden platform training in the Morris water task for Lis1 heterozygous mutant and wild-type mice. Quadrant search time and number of platform crossings are presented for both the day 2 (A,B) and day 3 (C,D) probe trials. Data for the training quadrant is significantly higher than the data for each of the other three quadrants, P < 0.02. Data for the training quadrant is significantly higher than the data for the quadrant to the right, P < 0.05, but not significantly higher than the data for the other two quadrants, P > 0.05. Data are represented as the mean (±s.e.m.).

Figure 6

Latency to find the visible platform in the Morris water task for Lis1 heterozygous mutant and wild-type mice. There were no significant differences between +/− (○) and +/+ (●) mice (P > 0.9). Data are represented as the mean (±s.e.m.).

Figure 7

Time spent walking on top of the rotating rod across nine test trials for Lis1 heterozygous (+/−) mutant and wild-type (+/+) mice that were characterized as using an active- or passive-performing strategy (see text for details). +/+ mice stayed walking on top of the rotarod significantly longer than +/− mice (P < 0.00001). Mice characterized as passive-performing stayed on top of the rotarod significantly longer than active-performing mice (P < 0.02). Data are represented as the mean (±s.e.m.).

Figure 8

(A) Latency to find the hidden platform during the training phase of the random platform test in the Morris water task for Lis1 heterozygous (○, +/−) mutant and wild-type (●, +/+) mice. (*) Escape latencies are significantly different (P) < 0.007) between +/+ and +/− mice. (B) The average time to locate the platform during the random platform test trials. Data are the average escape latency for the three trials when the platform was in the trained site compared to the three trials when the platform was in the other sites. (C) The average number of platform crossings during the random platform test. For the trained site, data are the average number of platform crossings during the three trials that the platform was located in the other sites. For the other sites, data are the average number of platform crossings for all three of the other sites during the three trials that the platform was located in the trained site.* Significant difference (P < 0.005) between the trained site and other site data. Data are represented as the mean (±s.e.m.).