Early Retinal Defects in Fmr1-/y Mice: Toward a Critical Role of Visual Dys-Sensitivity in the Fragile X Syndrome Phenotype? - PubMed (original) (raw)

doi: 10.3389/fncel.2018.00096. eCollection 2018.

Olivier Perche 1 2 3, Maryvonne Ardourel 2 3, Audrey Bazinet 2 3, Arnaud Pâris 2 3, Rafaëlle Rossignol 2 3, Géraldine Meyer-Dilhet 2 3, Anne-Laure Mausset-Bonnefont 4, Betty Hébert 2 3, David Laurenceau 1, Céline Montécot-Dubourg 2 3, Arnaud Menuet 2 3, Jean-Charles Bizot 5, Jacques Pichon 2 3, Isabelle Ranchon-Cole 6, Sylvain Briault 1 2 3

Affiliations

Early Retinal Defects in _Fmr1_-/y Mice: Toward a Critical Role of Visual Dys-Sensitivity in the Fragile X Syndrome Phenotype?

Olivier Perche et al. Front Cell Neurosci. 2018.

Abstract

Fragile X Syndrome (FXS) is caused by a deficiency in Fragile X Mental Retardation Protein (FMRP) leading to global sensorial abnormalities, among which visual defects represent a critical part. These visual defects are associated with cerebral neuron immaturity especially in the primary visual cortex. However, we recently demonstrated that retinas of adult _Fmr1_-/y mice, the FXS murine model, present molecular, cellular and functional alterations. However, no data are currently available on the evolution pattern of such defects. As retinal stimulation through Eye Opening (EO) is a crucial signal for the cerebral visual system maturation, we questioned the precocity of molecular and functional retinal phenotype. To answer this question, we studied the retinal molecular phenotype of _Fmr1_-/y mice before EO until adult age and the consequences of the retinal loss of Fmrp on retinal function in young and adult mice. We showed that retinal molecular defects are present before EO and remain stable at adult age, leading to electrophysiological impairments without any underlying structural changes. We underlined that loss of Fmrp leads to a wide range of defects in the retina, settled even before EO. Our work demonstrates a critical role of the sensorial dysfunction in the _Fmr1_-/y mice overall phenotype, and provides evidence that altered peripheral perception is a component of the sensory processing defect in FXS conditions.

Keywords: Fmrp; Fragile X syndrome; peripheral nervous system; sensorial dys-sensitivity; vision.

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Figures

Figure 1

Figure 1

Scotopic electroretinogram (ERG) in wild-type (WT) and _Fmr1_−/y (KO) mice at 3 and 6 months old. (A) Typical ERG for one flash stimulus with the (i) oscillatory potentials (OPs) in the b-wave ascending part and (ii) intensity–response function of a- and b-wave amplitudes are represented. (B) Representative (i) ERG and (ii) OPs traces obtained from WT or _Fmr1_−/y mice at 3 and 6 months old.

Figure 2

Figure 2

Scotopic ERG parameters measured in WT and _Fmr1_−/y (KO) mice at 3 and 6 months old. (A) Retinal function was assessed by recording ERG (WT n = 10 and _Fmr1_−/y n = 10 for each age). For each typical ERG obtained at light intensity −2.88 log(cd.s.m−2), the decreasing part of the a-wave was fitted to calculate the extrapolated maximal a-wave amplitude (_A_max). From the fitted b-wave sensitivity curve obtained by serial responses to increasing flash stimuli (−3.47 log(cd.s.m−2) to 0.6 log(cd.s.m−2)) we calculated the saturated b-wave amplitude (_B_max) and the n parameter (representing the b-wave sensitivity curves slope). Ratio _B_max/_A_max was also calculated. (B) OPs result in the ascending part of the b-wave. OPs were recorded by using a band-pass between 30 Hz and 300 Hz. For each OPs, the amplitude from the baseline to the peak and the latency were calculated. Data are presented as Mean ± SEM. Significant differences between WT and _Fmr1_−/y for one age time are noted by *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001.

Figure 3

Figure 3

Retinal histology and TUNEL assay in WT and _Fmr1_−/y (KO) mice. (A) Retinal layer structure was evaluated in vivo by OCT at 3 months old (WT n = 10 and _Fmr1_−/y n = 10; Scale bar, 50 μm) and (B) by histology techniques at 1 day post-natal (1DPN; WT n = 2 and _Fmr1_−/y n = 2) and at 1, 3 and 6 months old (noted WT1 and KO1, WT3 and KO3 and WT6 and KO6 respectively, WT n = 10 and _Fmr1_−/y n = 10 for each age; Scale bar, 20 μm; C) On the 3 and 6 months old sections, number of apoptotic cells per mm2, assessed by TUNEL assay, and total number of nuclei in the ONL and INL was counted (WT n = 5 and _Fmr1_−/y n = 5 for each age). Data are presented as Mean ± SEM (NbL, Neuroblastic Layer; ONL, Outer Nuclear Layer; OPL, Outer Plexiform Layer; INL, Inner Nuclear Layer; IPL, Inner Plexiform Layer or Ret: Total Retina).

Figure 4

Figure 4

Fragile X mental retardation protein (Fmrp), Rhodopsin and PSD95 mRNA and protein expressions in WT and _Fmr1_−/y (KO) mice at 1 DPN and 1, 3 and 6 months old. mRNA and protein expressions of (A) Fmrp, (B) Rhodopsin and (C) PSD95 were assessed by qPCR (n = 8 per group) and Western-blot (n = 5 per group) analysis in WT (white bars) and _Fmr1_−/y (gray bars) mice. For qPCR, data are expressed as 2−ΔCt values and normalized to 18S RNA internal control. For Western-blot, data are presented as Mean ± SEM in percentage of WT aged of 1 DPN. (D) A representative Western-blot experiment obtained for WT and _Fmr1_−/y (KO) mice is presented for each protein at 1 DPN, 1 and 6 months old. Significant differences between groups are noted by **p < 0.01; ***p < 0.001; ****p < 0.0001.

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