FMR protein: Evidence of an emerging role in retinal aging?

Aging is a multifactorial process that affects the entire organism by cumulative alterations. Visual function impairments that go along with aging are commonly observed, causing lower visual acuity, lower contrast sensitivity, and impaired dark adaptation. Electroretinogram analysis revealed that the amplitudes of rod- and cone-mediated responses are reduced in aged mice and humans. Reports suggested that age-related changes observed in both rod and cone photoreceptor functionality were linked to oxidative stress regulation or free radical production homeostasis. Interestingly, several recent reports linked the fragile X mental retardation protein (FMRP) cellular activity with oxidative stress regulation in several tissue including brain tissue where FMRP participates to the response to stress via protein translation in neurite or is involved in free radical production and abnormal glutathione homeostasis. Based on these recent literatures, we raised the question about the effect of FMRP absence in the aging retina of Fmr1^-/y compared to their WT littermates. Indeed, up to now, only young or adult mice (<6 months) were investigated and have shown a specific retinal phenotype. Herein, we demonstrated that Fmr1^-/y mice do not present the aging effect on retinal function observed in WT littermates since ERG a- and b-waves amplitudes as well as oscillatory potentials amplitudes were not collapsed with age (12/18 months old). Absence of FMRP and its consequences seem to protect the retina against aging effect, rising a pivotal role of FMRP in retinal aging process.

Fragile X Mental Retardation Protein expression in the retina is regulated by light

Fragile X Mental Retardation Protein (FMRP) is a RNA-binding protein that modulates protein synthesis at the synapse and its function is regulated by glutamate. The retina is the first structure that participates in vision, and uses glutamate to transduce electromagnetic signals from light to electrochemical signals to neurons. FMRP has been previously detected in the retina, but its localization has not been studied yet. In this work, our objectives were to describe the localization of FMRP in the retina, to determine whether different exposure to dark or light stimulus alters FMRP expression in the retina, and to compare the pattern in two different species, the mouse and chick. We found that both FMRP mRNA and protein are expressed in the retina. By immunohistochemistry analysis we found that both mouse and chick present similar FMRP expression localized mainly in both plexiform layers and the inner retina. It was also observed that FMRP is down-regulated by 24 h dark adaptation compared to its expression in the retina of animals that were exposed to light for 1 h after 24 h in the dark. We conclude that FMRP is likely to participate in retinal physiology, since its expression changes with light exposure. In addition, the expression pattern and regulation by light of FMRP seems well conserved since it was similar in both mouse and chick.

Origin of type I collagen localized within oviduct epithelium of quail hyperstimulated by progesterone

Bird oviduct development is controlled by sex steroid hormones. Estrogens (E) induce cell proliferation, formation of tubular glands by epithelial cell evagination and cell differentiation. Progesterone (P) strongly increases secretory processes in E-treated quails, but inhibits cell proliferation and cell evagination. The balance between E and P is very critical for the development and morphogenesis of the oviduct. After six daily injections of low doses of E (10 micrograms day-1) and high doses of P (5 mg day-1) into ovariectomized quails, cell proliferation and secretory process are stimulated but cell evagination is totally inhibited and distribution of striated collagen is perturbed. Using antibodies against type I collagen the stroma, which is mainly composed of fibroblasts, is brightly stained, as are some regions within the epithelium. Electron microscopy shows that bundles of striated collagen fibrils appear in extracellular spaces between the lateral membranes of the epithelial cells or between the basal lamina and the epithelial basal membrane. After in situ hybridization using a 35S riboprobe specific for mRNA of the alpha 2 chain of type I collagen, mRNA was detected only in the fibroblasts of the stroma and not in epithelial cells. Furthermore electron microscope studies of collagen bundles in serial sections clearly show collagen fibrils passing through the basal lamina. It is assumed that the type I collagen between epithelial cells originates from mesenchymal cells. In the oviduct of immature birds or after physiological E + P stimulation, striated collagen is localized only in the stroma and never within the epithelium. These results indicate a modulation of extracellular matrix by sex steroid hormones in the quail oviduct.

Immunolocalization of laminin during estrogen-induced differentiation of quail oviduct epithelial cells

During estrogen-induced development of the quail oviduct, tubular glands are formed by evagination of epithelial cells into the stroma. The distribution of laminin was studied during the early stages by means of immunofluorescence and immunoperoxidase techniques. Ultrastructural changes in the basal lamina were studied by electron microscopy. Basement membranes at all stages of development were delineated with 3 polyclonal antilaminin antisera. However, in ovariectomized birds, laminin could not be detected by one of the polyclonal antilaminin antisera. Subsequently, this antibody detected laminin as epithelial cell evaginations were induced by estradiol benzoate. The heavy and light chains of Engelbreth Holm sarcoma (EHS) laminin were revealed in immunoblotting by all antibodies. By electron microscopy after the immunoperoxidase technique with antilaminin antisera laminin appears to be accumulated mainly in the lamina densa. Furthermore, the thickness of the basal lamina increases during oviduct development. These data indicate that basal lamina organization is modified during oviduct cell differentiation and that immunoreactivity of epithelial basement membrane laminin changes during development.