Modeling Fragile X Syndrome: Characterizing Fmr1 Gene Knockout Mice across Genotype, Behavior, and Morphology

Abstract

Objective: Fragile X syndrome (FXS) is a hereditary condition resulting from dynamic mutations in the Fmr1 gene, leading to reduced or absent fragile X mental retardation protein (FMRP). Although molecular genetic diagnostics for FXS have advanced, there is currently a lack of effective clinical treatment. Hence, identifying a suitable FXS animal model is crucial for FXS therapeutic studies. This study primarily aims to evaluate whether Fmr1 mice display aberrant behaviors similar to those observed in human FXS patients, aiming to validate their feasibility as a model for FXS. Research Design and Methods: Polymerase chain reaction and immunoblotting were employed to genotype Fmr1 knockout (KO) mice and wild-type (WT) mice. Using hematoxylin and eosin staining and Golgi staining, testicular and dendritic spine morphology in both animal groups was observed. The animals were subjected to audiogenic seizure (AGS) observation, evaluating their learning and memory levels using the water maze and light avoidance methods, while their exploratory behavior capacity was assessed using the open-field and autonomous activity experiments. Anxiety behavior was evaluated using the elevated plus maze. Results: WT mice produced a 500 bp DNA fragment, while KO mice yielded an 800 bp fragment. KO mice exhibited a lack of FMRP expression, notably increased dendritic spine length and density, and presented with macroorchidism. KO mice showed increased susceptibility to AGS. In the Morris water maze experiment, KO mice displayed significantly increased escape latency and platform crossings. The spatial search experiment revealed that KO mice spent significantly less time in the target quadrant compared to WT mice. The light-avoidance and platform experiments indicated a significant reduction in latency for KO mice but an increase in errors. In the open-field experiment, KO mice spent significantly more time and made more entries into the central zone compared to WT mice. KO mice exhibited increased total travel distance and speed. The elevated plus maze experiment showed that KO mice spent significantly more time, made more entries, and traveled further in the open area compared to WT mice. The autonomous activity experiment revealed that KO mice had significantly more activity counts than WT mice but fewer standing counts. Conclusions: Findings from genotype, protein expression spectrum, morphology, and behavioral results suggest that Fmr1 gene KO mice demonstrate phenotypes similar to those observed in human FXS, making them a potential model for future FXS research. These phenotypes are associated with the absence of FMRP expression.

Keywords

• behavioral studies
• fmr1
• fragile x mental retardation protein
• fragile x syndrome
• genotype
• morphology