Segmental and restricted localization pattern of Fras1 in the developing meningeal basement membrane in mouse

Abstract

The Fras1/Frem family of extracellular matrix proteins consists of Fras1 and its structurally related proteins, Frem1 (Fras1-related extracellular matrix protein 1), Frem2 and Frem3. These are co-localized in embryonic epithelial basement membranes (BMs), where they contribute to epithelial-mesenchymal adhesion. Although Fras1 localization pattern in epithelial BMs has been well defined, it has not yet been comprehensively studied in the central nervous system. Here, we demonstrate the immunohistochemical profile of Fras1 in the developing mouse brain and reveal an exclusively meningeal BM protein deposition. Interestingly, Fras1 displays a segmental localization pattern, which is restricted to certain regions of the meningeal BM. Frem2 protein displays a similar localization pattern, while Frem3 is rather uniformly distributed throughout the meningeal BM. Fras1 and Frem2 proteins are detected in regions of the BM that underlie organizing centers, such as the roof plate (RP) of diencephalon, midbrain and hindbrain, and the RP-derived structures of telencephalon (choroid plexus and hem). Organizing centers exert their activity via the production of bioactive molecules, which are potential Fras1 ligands. The restricted pattern of Fras1 and Frem2 proteins indicates a molecular compartmentalization of the meningeal BM that could reflect, yet unspecified, functional and structural differences.

Behavioural effects of extracellular matrix protein Fras1 depletion in the mouse

“…Our findings indicate a possible involvement of Fras1 in the function of widespread brain areas, some of which lie deep in the brain parenchyma, remotely located from the meningeal BM, where Fras1 protein has been detected in the developing murine brain (Makrygiannis et al, 2013). Although the Fras1 gene is expressed in certain brain regions of juvenile mice, the corresponding protein could not be detected in neural tissue regardless of the different immunohistochemical methods applied.…”

“…The fluorescent protein signal was exclusively detected in embryos and neonates (P1) in the BM of choroid plexuses and in the meningeal BM (Figure 2f, g). It is noteworthy that Fras1 was not uniformly distributed throughout the embryonic meningeal BM but was rather spatially restricted, overlying certain brain regions, such as the hem, the septum and the medial prefrontal cortex, the preoptic area, the dorsal and the posterior–ventral diencephalon, and the dorsal and ventral midline of the midbrain and hindbrain (Makrygiannis et al., 2013). Although the mRNA in situ hybridization experiments revealed expression of Fras1 in various regions of the foetal and juvenile mouse brains, in immunohistochemical assays the specific for Fras1 antibodies identified the protein exclusively in the meningeal and choroidal BM and not within the nervous tissue.…”

“…Fras1 is the founding member of the family of extracellular matrix proteins Fras1/Frem, which are co‐localized in the sublamina densa of embryonic epithelial BMs (Pavlakis et al., 2011). In addition to the extracellular deposition of Fras1/Frem in various epithelial BMs, they have also been detected in the meningeal BM surrounding the developing mouse brain and in the BM of choroid plexuses (Chiotaki et al., 2007; Dalezios, Papasozomenos, Petrou, & Chalepakis, 2007; Makrygiannis et al., 2013). In the present study, we investigated the expression of Fras1 transcripts in foetal (E12.5) and juvenile (P30) mouse brains by mRNA in situ hybridization experiments.…”

“…All family members have been detected in the basement membrane (BM) of several embryonic epithelia in mammals (Chiotaki et al., 2007; Petrou, Pavlakis, Dalezios, & Chalepakis, 2007), including certain regions of the meningeal BM, which encloses the central nervous system (Makrygiannis, Pavlakis, Petrou, Kalogeraki, & Chalepakis, 2013). Consistent with their localization in the BM, Fras1/Frem proteins confer structural cohesion between the epithelium and the surrounding mesenchyme (Pavlakis et al., 2011).…”

The Histochem Cell Biol conspectus: the year 2013 in review

“…The family of Fras1/Frem extracellular matrix proteins comprises four structurally related members, Fras1, Frem1, Frem2, and Frem3, which are colocalized in embryonic epithelial basement membranes and contribute to epithelial-mesenchymal adhesion. Makrygiannis et al (2013) have studied the Fras1/Frem family in the developing mouse brain and revealed an exclusively meningeal basement membrane protein deposition. Furthermore, Fras1 displayed a segmental localization pattern since it was restricted to certain regions of the meningeal basement membrane.…”