Impaired spatial learning strategies and novel object recognition in mice haploinsufficient for the dual specificity tyrosine-regulated kinase-1A (Dyrk1A)

Abstract

Background: Pathogenic aneuploidies involve the concept of dosage-sensitive genes leading to over- and underexpression phenotypes. Monosomy 21 in human leads to mental retardation and skeletal, immune and respiratory function disturbances. Most of the human condition corresponds to partial monosomies suggesting that critical haploinsufficient genes may be responsible for the phenotypes. The DYRK1A gene is localized on the human chromosome 21q22.2 region, and has been proposed to participate in monosomy 21 phenotypes. It encodes a dual-specificity kinase involved in neuronal development and in adult brain physiology, but its possible role as critical haploinsufficient gene in cognitive function has not been explored.

Methodology/principal findings: We used mice heterozygous for a Dyrk1A targeted mutation (Dyrk1A+/-) to investigate the implication of this gene in the cognitive phenotypes of monosomy 21. Performance of Dyrk1A+/- mice was assayed 1/ in a navigational task using the standard hippocampally related version of the Morris water maze, 2/ in a swimming test designed to reveal potential kinesthetic and stress-related behavioral differences between control and heterozygous mice under two levels of aversiveness (25 degrees C and 17 degrees C) and 3/ in a long-term novel object recognition task, sensitive to hippocampal damage. Dyrk1A+/- mice showed impairment in the development of spatial learning strategies in a hippocampally-dependent memory task, they were impaired in their novel object recognition ability and were more sensitive to aversive conditions in the swimming test than euploid control animals.

Conclusions/significance: The present results are clear examples where removal of a single gene has a profound effect on phenotype and indicate that haploinsufficiency of DYRK1A might contribute to an impairment of cognitive functions and stress coping behavior in human monosomy 21.

Figure 1. Morris water maze test.

Morris water maze performance in Dyrk1A+/− and wild type animals during the learning sessions expressed as (A) latency (s) to find the platform along the acquisition phase, cue and reversal sessions; (B) mean swimming speed; (C) total distance traveled and (D) time spent in the target quadrant during the removal session; discontinuous lines represent the chance level in this session. White bars and circles represent wild types and black bars and circles represent Dyrk1A +/−. Data are represented as mean±SEM; * P<0,05, Student's t test. Abbreviations: REV, reversal session; NE, northeast; NW, northwest; SW, southwest; SE, southeast.

Figure 2. Non-searching strategies in the Morris water maze test.

Floating behavior (A and B) was operationally defined as any period equal to or longer than 5 s, during which the average mouse swimming speed stayed below 3 cm.s⁻¹. (A) Number of floating episodes; (B) Cumulative floating time (s); (C) Time in center-periphery during acquisition sessions. Dyrk1A+/− (black bars) mice spent more time in peripheral zone than control mice (white bars) during acquisition sessions. Dotted curves show the decrease of time in the peripheral zone between the first and fourth acquisition session. (D) Time (%) in center-periphery calculated for the cued, removal and reversal sessions. Data are shown as mean±SEM. ** P<0,005, Student's t test. Abbreviations: REM, removal session; REV, reversal session; C, center; P, periphery.

Figure 3. Learning strategies in the Morris water maze test.

(A) and (B) represent the spatial preference of Dyrk1A+/− and Dyrk1A+/+ mice along four acquisition sessions. (A) Representative swim paths of a wild type and a Dyrk1A+/− mouse illustrating that Dyrk1A+/− mouse swam more irregularly than the control mouse. (B) Color-coded histograms representing occupancy of wild type (upper panel) and mutant (lower panel) mice during the acquisition sessions of the hidden platform version of Morris Water Maze task. The wild type mice focused their search in the trained location (where the platform used to be during training) whereas the mutant mice visited the whole maze area equivalently. Color scale is given on the right of the histograms. (C) Cumulative permanence in quadrants. Percentage of time in quadrants of mice spends in four acquisition sessions and cue session. Each quadrant is represented by a different color. (D) Cumulative search error. Dyrk1A+/− mice (black bars) and control littermates (white bars) summed one-second averages corrected for the particular start location and platform location by subtracting the proximity score that would be produced by perfect performance on that trial. (E) Whishaw's index. Dyrk1A+/− mice revealed decreased percentage of time spent in correct corridor. Data are shown as mean±SEM (wild types, n = 12; Dyrk1A+/−, n = 11; * P<0,05; **, P<0,005, Student's t test). Abbreviation: REM, removal session.

Figure 4. Swimming Test.

(A) Swimming test with water temperature at 25°C reveals that the swimming speed between Dyrk1A+/+ and Dyrk1A+/− mice is similar during a 60 s trial period. Inset: Total mean speed and distance traveled by Dyrk1A+/− and wild type mice. (B) Swimming test with water temperature at 17°C reveals a significant reduction of the swimming speed in the mutants compared to wild types, allowing detecting a hypoactive behavior under stressful environmental conditions. Inset: total mean speed and distance traveled by mutant animals mice were less than wild type mice. Open circles (Dyrk1A+/+) and black circles (Dyrk1A+/−) represent means±SEM.

Figure 5. Object recognition test.

(A) Schematic representation of the object recognition test. Mice are allowed to explore an identical pair of objects, and after 24 hours, they are presented with the familiar object and a new object. (B) Dyrk1A+/− exhibited significantly impaired novel object recognition as shown by the similar amount of time spent in exploring the two objects (familiar and new). (C) Dyrk1A+/− showed no net preference between novel and familiar objects as shown by the reduced discrimination index. White bars (Dyrk1A+/+) and black bars (Dyrk1A+/−) represent means±SEM.