In-vivo and ex-vivo analysis of wild-type and knock-out mice for fmr1 gene

Fragile X syndrome (FXS) is the leading cause of genetically transmitted autism and intellectual disability. It is primarily caused by an excessive repetition of CGG triplets in the promoter of the FMR1 gene, which encodes the Fragile X syndrome Mental Retardation Protein (FMRP). This leads to epigenetic silencing by hypermethylation and to the consequent loss of FMRP, a protein essential for mRNA translational regulation and trafficking especially in the brain. FMRP loss results in impaired synaptic plasticity and multifaceted disorders, significantly impacting brain areas like the hippocampus, crucial for mood and cognition regulation. Emerging evidence shows that perineuronal nets (PNNs) are plasticity players critically involved in learning and memory processes and their expression is reduced in the hippocampus of FXS mice. In this thesis work, the mouse model for FXS (Fmr1KO mice) was used to conduct both in vivo and ex vivo analyses. After behavioral phenotyping, mice were sacrificed at 40 days old, and 40 µm brain slices were obtained using a cryostat. Following immunohistochemistry, imaging analysis was performed. Approximately 30 slice images of each mouse brain (four Fmr1KO males and four WT males) were aligned to the mouse brain atlas using ABBA, an ImageJ plugin. Subsequently, PNN and parvalbumin (PV) positive cells, as well as cells positive for both PNNs and PV were manually counted in the dorsal hippocampus. The aim of this study was to correlate possible hippocampal plasticity alterations with FXS behavioral deficits.