Abstract
Purpose :
The lens resides in a low oxygen environment resulting in a hypoxic gradient from the surface to the core. This results in a sharp drop in oxygen levels beginning in the transition zone where immature fiber cells initiate their terminal differentiation program. In previous studies we have demonstrated that that lens hypoxia activates transcription factor HIF1 that both activates and represses genes specific for lens epithelia cells and fiber cells. The purpose of the present study was to determine the identity and temporal sequence of genes expressed in the lens upon hypoxic exposure and to identify the functional pathways linked to the lens hypoxic response.
Methods :
Day 13 embryonic chick lenses were exposed to 2, 4, 6, 8 and 24 hours of 1% oxygen in a hypoxia chamber and RNA was prepared and analyzed by RNAseq. Differentially expressed transcripts were identified, the data analyzed by PCA analysis and transcripts exhibiting statistically significant levels of differential gene expression grouped by temporal expression patterns. Temporally distinct clusters of genes were analyzed for representation in functional pathways by Enrichr and important lens differentiation pathways identified.
Results :
The data identified distinct clusters of genes following hypoxic exposure. 244, 1020, 1210, 1295 and 1927 genes were identified to be differentially upregulated at 2, 4, 6, 8 and 24 hours following hypoxic exposure relative to 0 hours. Strikingly, the majority of activated genes have expression patterns specific for lens fiber cells while the majority of repressed genes exhibited expression patterns specific for lens epithelial cells. Functional clustering of the identified genes identified multiple pathways including those previously identified to be important for achieving the structure and function of mature lens fiber cells.
Conclusions :
The results identify that the lens hypoxic response is characterized by temporally distinct waves of gene expression corresponding with distinct lens epithelia or fiber cell functions. Future analysis of the transcription factors and epigenetic control pathways governing the expression of these genes will provide a roadmap of the process of hypoxia-driven lens differentiation.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.