# Blastocyst-like Structures in the Peripheral Retina of Young Adult Beagles

## TL;DR

This study found blastocyst-like structures in the retinas of adult beagles, possibly formed by retinal stem cells and migrating RPE cells.

## Contribution

The discovery of blastocyst-like structures in adult retinas suggests novel mechanisms of retinal cell interaction and development.

## Key findings

- Small cysts in the inner retina showed strong positivity for stem cell and blastocyst markers.
- RPE65-positive cells surrounded the cysts, indicating possible migration from retinal pigment epithelium.
- The structures resembled blastocysts, potentially formed by interactions between retinal stem cells and RPE cells.

## Abstract

In this immunohistological study on the peripheral retina of 3-year-old beagle dogs, excised retina specimens were immunostained with antibodies against nestin, Oct4, Nanog, Sox2, CDX2, cytokeratin 18 (CK 18), RPE65, and YAP1, as well as hematoxylin and DAPI, two nuclear stains. Our findings revealed solitary cysts of various sizes in the inner retina. Intriguingly, a mass of small round cells with scant cytoplasms was observed in the cavity of small cysts, while many disorganized cells partially occupied the cavity of the large cysts. The small cysts were strongly positive for nestin, Oct4, Nanog, Sox2, CDX2, CK18, and YAP1. RPE65-positive cells were exclusively observed in the tissue surrounding the cysts. Since RPE65 is a specific marker of retinal pigment epithelial (RPE) cells, the surrounding cells of the peripheral cysts were presumably derived from RPE cells that migrated intraretinally. In the small cysts, intense positive staining for nestin, a marker of retinal stem cells, seemed to indicate that they were derived from retinal stem cells. The morphology and positive staining for markers of blastocyst and RPE cells indicated that the small cysts may have formed structures resembling the blastocyst, possibly caused by the interaction between retinal stem cells and migrated RPE cells.