Monday, April 29, 2024
4/29/2024
Abstract Smith-Magenis syndrome (SMS) is a rare neurodevelopmental disorder characterized by low intellectual quotient, altered sleep cycles, obesity, and behavioral problems. The major gene contributing to SMS is Retinoic acid-induced 1 (RAI1). RAI1 is a chromatin-binding protein that participates in regulating circadian clock genes. Every reported individual with SMS experienced circadian rhythm disturbances in sleep/wake cycle such as daytime sleepiness, frequent nighttime awakenings, and decreased total sleep time beginning in early childhood. SMS is also the only known genetic disorder with inverted circadian rhythm of melatonin production. However, how RAI1 loss impairs circadian rhythms and cognitive function remains unknown. A major roadblock to understanding the etiology of SMS is a lack of appropriate animal models that recapitulate circadian rhythm disturbance. Most inbred laboratory mice, in which Rai1 was deleted, are melatonin-deficient, thus inadequate for testing this hormone’s impact. Although Rai1-knockout (KO) mice have provided important insights into the SMS etiology, including an apparent obesity phenotype due to hyperphagia, Rai1-KO mice do not phenocopy sleep rhythm disturbance observed in SMS patients. Contrary to the frequent night awakening and total sleep loss seen in SMS patients, Rai1-KO mice had even better rhythms sleeping significantly more during the resting phase than wild-type mice. Two factors could have contributed to the striking differences between Rai1-KO mice and SMS patients; 1) differential melatonin productions and 2) distinct neural mechanisms that generate the opposite chronotypes between the nocturnal laboratory mice and diurnal humans. To address the fundamental needs of diurnal models of RAI1 deficiency, we set out Rai1 gene targeting in Nile grass rat, Arvicanthis niloticus, a diurnal rodent species. Nile grass rat is a well-established diurnal rodent used in circadian research for almost 30 years. Leveraging on the genome sequence recently released by the Genome10K project and CRISPR-mediated gene editing, we have generated Rai1-KO Nile grass rats, the first genome-edited diurnal rodent to our knowledge. Importantly, the first Rai1-KO phenocopy the rhythm disturbances as seen in SMS patients. This novel model allows us to elucidate the role of the Rai1 gene in regulating circadian rhythms and cognitive function in diurnal animals that can be translated to humans. The proposed project aims to thoroughly validate the specific gene deletion and perform initial behavioral characterization of Rai1-deficient Nile grass rats, thereby providing the first diurnal animal system to study SMS pathophysiology and a platform to test therapeutic interventions for this condition.
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