| Abstract |
The Fras1/Frem protein family of extracellular matrix components comprises of four members, Fras1, Frem1, Frem2 and Frem3. They are principally localized in epithelial basement membranes during embryogenesis, contributing in the structural and functional conjunction of embryonic epithelium with the subjacent mesenchyme. Nevertheless, Fras1 protein has been implied for a role in development and function of brain, such as the occasionally exhibited psychomotor/ developmental delay in patients with Fraser Syndrome. The aim of the present dissertation is to elucidate the role of Fras1 in the brain development and function, focusing on two main axes: determination of its localization profile in the murine brain during development and adulthood, as well as comparative analysis of development, anatomy and function of telencephalon in the context of differential Fras1 expression.
In situ hybridization revealed the Fras1 mRNA expression pattern, which included certain domains of embryonic and juvenile telencephalon (G.Chalepakis). Fras1 protein was immunohistochemically detected exclusively in embryonic meningeal basement membrane. The localization pattern of Fras1 in the basement membrane was segmental, overlying particular brain domains. However, Fras1 protein was not detected inside the neural tissue.
Subsequently, certain brain functions were investigated in Fras1-/- mice. The examined neural circuits are responsible for the expression of unconditioned and conditioned fear, anxiety and object discrimination. The comparative analysis of fear and anxiety in control and Fras1-/- mice was performed aiming to study the activity of amygdala. Our results revealed that mutant mice were able to express fear, which is attributed to active medial subnucleus of central amygdala. Nevertheless, the basolateral amygdala and the lateral subnucleus of central amygdala are possibly affected, since the mutant mice were unable to express the auditory conditioned fear.
The comparative histological analysis showed that the three examined amygdalar nuclei, which participate in fear circuit, were affected in Fras1-/- mice. The defects were predominantly localized in the main intercalated nucleus and rostral portion of central amygdala, detected from birth onwards, reminiscent of a potential developmental phenotype. The aberrant morphology of anterior amygdala in Fras1-/- mice was confirmed utilizing specific neuronal markers, such as Ctip2, Foxp1, Foxp2 and Tbr1. The aforementioned defects might cause the alterations as much in auditory fear conditioning, as in regulation of fear expression in mutant mice.
Hippocampus came under investigation, featuring the behavioral experiment of novel object recognition and histological analysis. Fras1-/- mice displayed normal familiar-novel object discriminatory ability. However, the comparative histological and molecular analysis of hippocampus showed a differential arrangement of cornu ammonis subdomains in Fras1-/- mice, where CA2 and CA3 subdomains were dorsally extended at the expense of CA1.
Fras1 στην ανάπτυξη και λειτουργία του τελικού εγκεφάλου
Furthermore, comparative histological and immunohistochemical analysis was implemented in neocortex and piriform. No differences were detected in neocortex but the parvalbumin positive interneurons were reduced in piriform of adult Fras1-/- mice. Finally, BrdU experiments revealed a slight retardation in brain development of Fras1-/- embryos, as well as affected neuronal migration during late stages of embryogenesis.
Recapitulating the results of the present dissertation, Fras1 protein was exclusively detected in meningeal basement membrane during mouse embryogenesis. Nevertheless, the Fras1-/- mice exhibited aberrant morphology of rostral amygdala and hippocampus during postnatal stages. Furthermore, Fras1-/- adult mice displayed abnormal stress behaviors which are amygdala-dependent. Those findings lead us to postulate a wider role for Fras1 in telencephalon development and function that remains to be investigated.
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Η συμβολή της εξωκυττάριας πρωτεΐνης Fras1 στην ανάπτυξη και λειτουργία του τελικού εγκεφάλου στα ποντίκια
