Loss of cGMP-dependent protein kinase II alters ultrasonic vocalizations in mice, a model for speech impairment in human microdeletion 4q21 syndrome

Chromosome 4q21 microdeletion leads to a human syndrome that exhibits restricted growth, facial dysmorphisms, mental retardation, and absent or delayed speech. One of the key genes in the affected region of the chromosome is PRKG2, which encodes cGMP-dependent protein kinase II (cGKII). Mice lacking cGKII exhibit restricted growth and deficits in learning and memory, as seen in the human syndrome. However, speech/vocalization impairments in these mice have not been determined. Moreover, the molecular pathway underlying speech impairment in humans is not fully understood. Here, we employed cGKII knockout (KO) mice as a model for the human microdeletion syndrome to test whether vocalizations are affected by loss of the PRKG2 gene. Mice emit ultrasonic vocalizations (USVs) to communicate in social situations, stress, and isolation. We thus recorded ultrasonic vocalizations as a model for speech in humans. We isolated postnatal day 5-7 pups from the nest to record and analyze USVs and found significant differences in vocalizations of KO mice relative to wild-type and heterozygous mutant mice. KO mice produced fewer calls that were shorter duration, higher frequency, and lower intensity. Because neuronal activity in the hypothalamus is important for the production of animal USVs following isolation from the nest, we assessed hypothalamic activity in KO pups following isolation. Indeed, we found abnormal hyperactivation of hypothalamic neurons in cGKII KO pups after isolation. Taken together, our studies indicate that cGKII is important for neuronal activation in the hypothalamus, which is required for the production of USVs in neonatal mice. We further suggest cGKII KO mice can be a valuable animal model for human microdeletion 4q21 syndrome.