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:

Molecular characterization of an aquaporin cDNA from brain: candidate osmoreceptor and regulator of water balance. The aquaporins transport water through membranes of numerous tissues, but the molecular mechanisms for sensing changes in extracellular osmolality and regulating water balance in brain are unknown. We have isolated a brain aquaporin by homology cloning. Like aquaporin 1 (AQP1, also known as CHIP, channel-forming integral membrane protein of 28 kDa), the deduced polypeptide has six putative transmembrane domains but lacks cysteines at the known mercury-sensitive sites. Two initiation sites were identified encoding polypeptides of 301 and 323 amino acids; expression of each in Xenopus oocytes conferred a 20-fold increase in osmotic water permeability not blocked by 1 mM HgCl2, even after substitution of cysteine at the predicted mercury-sensitive site. Northern analysis and RNase protection demonstrated the mRNA to be abundant in mature rat brain but only weakly detectable in eye, kidney, intestine, and lung. In situ hybridization of brain localized the mRNA to ependymal cells lining the aqueduct, glial cells forming the edge of the cerebral cortex and brainstem, vasopressin-secretory neurons in supraoptic and paraventricular nuclei of hypothalamus, and Purkinje cells of cerebellum. Its distinctive expression pattern implicates this fourth mammalian member of the aquaporin water channel family (designated gene symbol, AQP4) as the osmoreceptor which regulates body water balance and mediates water flow within the central nervous system.
{"Gene": ["CHIP", "mercury-sensitive sites", "channel-forming integral membrane protein of 28 kDa", "aquaporin water channel", "AQP4", "AQP1", "mercury-sensitive site", "aquaporin 1", "transmembrane domains"]}