Genome-wide screening reveals the genetic basis of mammalian embryonic eye development

Characterisation of SLC38A8 and Its Role in Retinal Pathways and Disease

BACKGROUND

This study investigates the role of the SLC38A8 gene. SLC38A8 facilitates glutamine influx, which converts to glutamate in the visual pathway. Mutations in SLC38A8 are associated with FHONDA syndrome, a subtype of foveal hypoplasia with congenital nystagmus and optic-nerve-decussation defects without pigmentation leading to severe vision loss.

METHODS

In vivo and in vitro methods were conducted using retinal cell lines overexpressing SLC38A8, and Slc38a8/Slc38a7 gene-edited mice to evaluate visual function and physiological changes. Statistical analyses included two-way ANOVA, multiple regression, and ANCOVA.

RESULTS

In vitro, SLC38A8 overexpression influenced retinal gene expression, light detection, and visual perception, as well as glutamine and glutamate dynamics. In Y79SNAT8-OE cells, glutamate levels were significantly higher under light conditions compared to dark conditions at 12 h (3.4 ± 0.16 nmol/μl vs. 3.9 ± 0.17 nmol/μl, p = 0.0011) and 17 h (3.6 ± 0.22 nmol/μl vs. 4.5 ± 0.24 nmol/μl, p = 0.0001), a pattern not observed in control cells. SLC38A8 expression also increased significantly (RQ = 2.1 ± 0.11, p < 0.05) in Y79 cells under glutamine deprivation. In vivo, Slc38a8-truncated gene mice exhibited altered testicular morphology, with significantly reduced volume (70.9 ± 5.1 mm3 vs. 85.5 ± 6.7 mm3, p = 0.023), and reduced length (4.8 ± 0.2 mm vs. 5.4 ± 0.4 mm, p = 0.0169), alongside degenerative changes in germinal epithelium, and elevated liver enzyme. Despite normal eye morphology, retinal thickness, and visual evoked potentials, electroretinogram and behavioural tests indicated enhanced scotopic responsiveness with significant increases in a-wave (162.98 ± 14.1 μv vs. 133.9 ± 36.9 μv, p = 1.5e-07) and b-wave amplitudes (274.82 ± 25.2 μv vs. 199.9 ± 56.1 μv, p = 3.02e-09).

CONCLUSIONS

Our findings underscore SLC38A8 role in retinal function and glutamine-glutamate metabolism, with clinical implications for FHONDA and potential future dietary intervention targeting glutamine or glutamate.

Mitf over-expression leads to microphthalmia and coloboma in Mitf-cre mice

The Mitf transcription factor is a critical regulator of the melanocyte lineage and eye development. Mitf activity in different cell types is controlled in part by ten alternative promoters and their resulting isoforms. A useful tool for melanocyte-based research, Mitf-cre was designed to express Cre from the Mitf-M promoter, which is melanocyte specific. However, Mitf-cre mice are also microphthalmic, perhaps because of insertional mutagenesis or disrupted gene expression. Here, we investigated these possibilities and described the eye phenotype. Targeted locus amplification indicated that the transgene integrated on chromosome 2, in between Spred1 and Meis2. The BAC transgene used to make Mitf-cre was larger than expected, carrying three upstream alternative promoters, Mitf-H, Mitf-D, and Mitf-B, which could express their isoforms intact off the transgene. RT-qPCR using eye tissue demonstrated a 5-fold increase in Mitf transcripts containing exon 1B1b, which is shared by Mitf-H, Mitf-D, and Mitf-B, while Spred1 and Meis2 did not differ in their expression. These findings clarify and support the usage of Mitf-cre in conditional mutagenesis in melanocytes. The specific over-expression of these isoforms, which are preferentially expressed in the RPE, presents a unique resource for those interested in eye development and coloboma.

Commentary: The International Mouse Phenotyping Consortium: high-throughput in vivo functional annotation of the mammalian genome

The International Mouse Phenotyping Consortium (IMPC) is a worldwide effort producing and phenotyping knockout mouse lines to expose the pathophysiological roles of all genes in human diseases and make mice and data available and accessible to the global research community. It has created new knowledge on the function of thousands of genes for which little to anything was known. This new knowledge has informed the genetic basis of rare diseases, posited gene product influences on common diseases, influenced research on targeted therapies, revealed functional pleiotropy, essentiality, and sexual dimorphism, and many more insights into the role of genes in health and disease. Its scientific contributions have been many and widespread, however there remain thousands of "dark" genes yet to be illuminated. Nearing the end of its current funding cycle, IMPC is at a crossroads. The vision forward is clear, the path to proceed less so.

Computational identification of disease models through cross-species phenotype comparison

The use of standardised phenotyping screens to identify abnormal phenotypes in mouse knockouts, together with the use of ontologies to describe such phenotypic features, allows the implementation of an automated and unbiased pipeline to identify new models of disease by performing phenotype comparisons across species. Using data from the International Mouse Phenotyping Consortium (IMPC), approximately half of mouse mutants are able to mimic, at least partially, the human ortholog disease phenotypes as computed by the PhenoDigm algorithm. We found the number of phenotypic abnormalities in the mouse and the corresponding Mendelian disorder, the pleiotropy and severity of the disease, and the viability and zygosity status of the mouse knockout to be associated with the ability of mouse models to recapitulate the human disorder. An analysis of the IMPC impact on disease gene discovery through a publication-tracking system revealed that the resource has been implicated in at least 109 validated rare disease-gene associations over the last decade.

Good manufacturing practice production of human corneal limbus-derived stromal stem cells and in vitro quality screening for therapeutic inhibition of corneal scarring

BACKGROUND

Mesenchymal stem cells in the adult corneal stroma (named corneal stromal stem cells, CSSCs) inhibit corneal inflammation and scarring and restore corneal clarity in pre-clinical corneal injury models. This cell therapy could alleviate the heavy reliance on donor materials for corneal transplantation to treat corneal opacities. Herein, we established Good Manufacturing Practice (GMP) protocols for CSSC isolation, propagation, and cryostorage, and developed in vitro quality control (QC) metric for in vivo anti-scarring potency of CSSCs in treating corneal opacities.

METHODS

A total of 24 donor corneal rims with informed consent were used-18 were processed for the GMP optimization of CSSC culture and QC assay development, while CSSCs from the remaining 6 were raised under GMP-optimized conditions and used for QC validation. The cell viability, growth, substrate adhesion, stem cell phenotypes, and differentiation into stromal keratocytes were assayed by monitoring the electric impedance changes using xCELLigence real-time cell analyzer, quantitative PCR, and immunofluorescence. CSSC's conditioned media were tested for the anti-inflammatory activity using an osteoclastogenesis assay with mouse macrophage RAW264.7 cells. In vivo scar inhibitory outcomes were verified using a mouse model of anterior stromal injury caused by mechanical ablation using an Algerbrush burring.

RESULTS

By comparatively assessing various GMP-compliant reagents with the corresponding non-GMP research-grade chemicals used in the laboratory-based protocols, we finalized GMP protocols covering donor limbal stromal tissue processing, enzymatic digestion, primary CSSC culture, and cryopreservation. In establishing the in vitro QC metric, two parameters-stemness stability of ABCG2 and nestin and anti-inflammatory ability (rate of inflammation)-were factored into a novel formula to calculate a Scarring Index (SI) for each CSSC batch. Correlating with the in vivo scar inhibitory outcomes, the CSSC batches with SI < 10 had a predicted 50% scar reduction potency, whereas cells with SI > 10 were ineffective to inhibit scarring.

CONCLUSIONS

We established a full GMP-compliant protocol for donor CSSC cultivation, which is essential toward clinical-grade cell manufacturing. A novel in vitro QC-in vivo potency correlation was developed to predict the anti-scarring efficacy of donor CSSCs in treating corneal opacities. This method is applicable to other cell-based therapies and pharmacological treatments.