You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Gene"].

Please return the output as a JSON object of the format: {"Gene": ["SSX", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

X-arrestin: a new retinal arrestin mapping to the X chromosome. We have been using a differential cDNA cloning approach to isolate human retina-specific and retina-enriched genes [1]. A 1,314 bp cDNA was isolated by this approach, representing a highly retina-specific message encoding a 388 amino acid protein showing 58%, 50%, and 49% homology to bovine beta-arrestin, and bovine and human retinal arrestin (S-antigen), respectively. Chromosomal mapping localized this new arrestin gene to the proximal long arm of the X chromosome, hence it was named X-arrestin. In situ hybridization demonstrated its expression in the inner and outer segments and the inner plexiform regions of the retina.
{"Gene": ["retinal arrestin", "X-arrestin", "beta-arrestin", "retina-specific and retina-enriched genes", "S-antigen"]}