Genetics of Iris Cell Types & Study of Iris Cell Origins

Article: Johns Hopkins Medicine Researchers Map the Cell Types of the Iris in Mice
Source: Johns Hopkins Medicine
Published: November 30, 2021 

Changes in iris morphology in response to dilation or constriction

The iris provides the aperture with which we control varying levels of light that reaches our retina. The iris also plays a role in a variety of eye conditions that affect inflammation, intraocular pressure, neurological assessment, etc. Researchers at Johns Hopkins wanted to further understanding of the iris through genetically mapping the different cell types of the mouse iris, tracking how gene expression affects iris musculature during constriction and dilation, and defining the developmental origins of iris cells. Single-cell RNA sequencing revealed four new types of cells in the iris: two types of iris stromal (structural) cells and two types of iris smooth muscle (sphincter) cells that enable constriction in response to light. Because iris muscle contraction is a relatively drastic physical change for such a delicate structure, the researchers wondered if changes in gene expression were involved. Genetic analysis showed that while there was not much change in gene expression between a relaxed mouse eye and a constricted one, there were dramatic differences in the genes expressed in the dilated mouse eye (specifically a gene called EGR1 in dilator muscle cells), when the iris tissue is most compressed. EGR1 is a gene that responds to changes in the cellular environment throughout the body, leading the researchers to hypothesize that it is upregulated in response to the physical stress. Finally, the researchers used a genetically engineered mouse model to follow the embryonic development of the neural crest. They report, "The majority of the iris cells came from the neural crest, which gives us a fundamental understanding of how the iris develops." They hope that the information will connect genetic similarities between the mouse and human eye, and offer clues to develop new diagnostic tests and treatments for diseases that affect the iris, such as anterior uveitis and aniridia, as well as aid in regenerative medicine for disorders of the eye.

My rating of this study: ⭐⭐⭐

Wang J, Rattner A, and Nathans J. "A transcriptome atlas of the mouse iris at single-cell resolution defines cell types and the genomic response to pupil dilation." eLife.  10:e73477. 16 November 2021. https://doi.org/10.7554/eLife.73477