Modeling rare gene variation to gain insight into the oldest biomarker in autism: construction of the serotonin transporter Gly56Ala knock-in mouse

Abstract

Alterations in peripheral and central indices of serotonin (5-hydroxytryptamine, 5-HT) production, storage and signaling have long been associated with autism. The 5-HT transporter gene (HTT, SERT, SLC6A4) has received considerable attention as a potential risk locus for autism-spectrum disorders, as well as disorders with overlapping symptoms, including obsessive-compulsive disorder (OCD). Here, we review our efforts to characterize rare, nonsynonymous polymorphisms in SERT derived from multiplex pedigrees carrying diagnoses of autism and OCD and present the initial stages of our effort to model one of these variants, Gly56Ala, in vivo. We generated a targeting vector to produce the Gly56Ala substitution in the Slc6a4 locus by homologous recombination. Following removal of a neomycin resistance selection cassette, animals exhibiting germline transmission of the Ala56 variant were bred to establish a breeding colony on a 129S6 background, suitable for initial evaluation of biochemical, physiological and behavioral alterations relative to SERT Gly56 (wildtype) animals. SERT Ala56 mice were achieved and exhibit a normal pattern of transmission. The initial growth and gross morphology of these animals is comparable to wildtype littermate controls. The SERT Ala56 variant can be propagated in 129S6 mice without apparent disruption of fertility and growth. We discuss both the opportunities and challenges that await the physiological/behavioral analysis of Gly56Ala transgenic mice, with particular reference to modeling autism-associated traits.

Serotonin transporter variant drives preventable gastrointestinal abnormalities in development and function

“…SERT Ala56 mice exhibit hyperserotonemia and behaviors that align broadly with the core diagnostic features of ASD (12,13,45). These traits support the use of SERT Ala56 mice as a model for analyzing potential contributions of 5-HT signaling abnormalities to ASD.…”

“…Animals were tested at 6-8 weeks of age. SERT Ala56 mice were generated on a 129S6 background (12). Experiments were carried out with confirmed homozygous WT and SERT Ala56 littermates.…”

“…Multiple hyperactive coding variants of SERT have been found in subjects with ASD (9)(10)(11). Knockin mice expressing the most common of these, SERT Ala56 (12), display hyperserotonemia, increased 5-HT clearance, and hypersensitivity of central 5-HT 1A and 5-HT 2A receptors, as well as repetitive behaviors and deficits of socialization that are reminiscent of ASD (13). The phenotype of SERT Ala56 mice suggests that the constitutively elevated activity of SERT in these animals interferes with the 5-HT signaling required for normal brain development and later function (14)(15)(16).…”

Autism gene variant causes hyperserotonemia, serotonin receptor hypersensitivity, social impairment and repetitive behavior

“…To explore the dependence of juvenile and adult behavior on early-life 5-HT manipulation and further understand the impact of the SERT Ala56 variant in vivo, we generated mice expressing SERT Ala56 from the native mouse Slc6a4 locus (22). Although SERT Ala56 mice exhibit normal growth and fertility (22), they display significantly increased CNS 5-HT clearance, enhanced 5-HT receptor sensitivity, and hyperserotonemia.…”

“…Although SERT Ala56 mice exhibit normal growth and fertility (22), they display significantly increased CNS 5-HT clearance, enhanced 5-HT receptor sensitivity, and hyperserotonemia. Even more striking, SERT Ala56 animals display alterations in a number of ASDrelevant behaviors.…”