The Impact of the Williams Syndrome Mutations on Neural
James S. McDonnell Foundation Collaborative Activity Award:
Project 3: Are there endogenous nonhuman primate models of Williams syndrome or other forms of hypersociability? (Amaral, Suomi, Korenberg).
As the social alterations become better characterized in the Williams syndrome subject, one step in developing the nonhuman primate model will be to determine whether there are rhesus monkeys that demonstrate hypersocial behavior patterns reminiscent of Williams syndrome. This will entail fairly wide scale screening of monkey populations at colonies at NIH, at the California Regional Primate Research Center (CRPRC) and perhaps at the other 7 national primate research centers. Strategies for the detection of hypersocial rhesus monkeys will involve observational studies of mature rhesus monkeys in colony situations (initially at NIH and UC Davis) and temperamental analysis of young rhesus monkeys at UC Davis and NIH associated facilities. The CRPRC currently has approximately 4,000 rhesus monkeys whereas the Laboratory of Comparative Ethology at NIH has access to two large free- ranging colonies of wild rhesus monkeys (approximately 1,000 monkeys on Cayo Santiago island in Puerto Rico and approximately 4,000 monkeys on Morgan Island, SC).
For detection of young hypersocial animals, we will capitalize on a program already under way at the CRPRC. All newborns at the CRPRC (approximately 300-350 animals are born each year) undergo a 24 hour withdrawal from their mothers at approximately 3-4 months of age. During this period, animals are run through an extensive battery of testing of emotionality, sociality and temperament that also focuses on basic physiological and psychological variables (Capitanio, 1999) that are highly predictive of temperament and sociality in adult animals. Tests include the Human Intruder developed by Kalin and colleagues (Kalin et al., 2001), the preferential looking test as employed by Bachevalier and colleagues (Bachevalier et al., 1993), and other tests of social responses developed at the CRPRC, (e.g., responses to videos of monkeys presenting threats versus appeasing gestures or to novel objects). This assessment is based on the observations of Kagan and colleagues that young children demonstrate marked differences in their reactivity to objects as early as 4 months of age that are correlated with later social behavior (Kagan et al., 1998). Highly reactive children at 4 months of age tend to become timid, less spontaneous and less social as preschoolers and preteens whereas low reactive infants are typically more outgoing and social. Given the early emergence of these temperamental traits, they are presumed to have, at least in part, a genetic basis. The search for hyper- and hyposocial adult animals will initially rely on interactions with experienced animal care technicians who have daily contact with the animal populations at NIH and the CRPRC and are good sources of information on unusual animal behavior. From previous experience with our colonies, we expect at least 30 hyper or hyposocial adult animals who will then be more intensively assessed using the ethogram of social behavior that has been used in the Amaral laboratory to select animals for lesions studies of social behavior (Emery et al., 2001).
Taken together, these assessments provide extremely useful information for determining those animals that show distinctly increased or decreased confidence and willingness to engage in social interactions. Once the putatively hypersocial animals are identified, they will undergo genetic analyses in the Korenberg laboratory employing blood samples. As a first step, we will determine whether some of these animals have undergone genetic modification analagous to that observed in Williams syndrome. As an additional screen for genetic changes in the Williams region, cardiac ultrasound will be used to evaluate the hypersocial animals for the heart lesion (a narrowed aorta) caused by deletion of elastin and seen in 90% of subjects with Williams syndrome.
This genetic analysis will involve an approach similar to that for humans. A physical map will be generated based on bacterial artificial chromosomes (BACs) which will then be used for both Williams deletion analyses as already established by the Korenberg laboratory. The mapping and sequencing effort will be integrated with the ongoing efforts funded by the NIH and will involve initial pooled screens of existing rhesus monkey BAC libraries followed by BAC End Sequencing. in collaboration with Shaying Zhao (TIGR).
We will determine the common structure of the single copy region and duplicated regions surrounding the region homologous to Williams syndrome. We will generate and test interphase/ metaphase chromosome preparations of the hypersocial rhesus monkeys. This work has already been initiated by Korenberg in the great Apes and Capuchin and similar techniques will be applied to the rhesus monkey. Although the genomic organization of the region may not be the same in rhesus and human, preliminary studies reveal that some of the regions close to the common deletion breakpoints in Williams were already duplicated prior to the deviation of old and new world monkeys and these may also predispose to deletions in the rhesus monkey.
While searching for a “Williams monkey” is admittedly a risky endeavor, regardless of the natural occurrence of such variants, establishing the map and sequence of the Williams region in rhesus monkeys is essential to eventually generating a primate model. Moreover, establishing the techniques for identifying highly responsive, hypersocial animals as well as low responsive, hyposocial animals will provide the framework for identifying genetic contributions to sociality. We are aware that genetic variations producing neurological disorders such as Friedreich ataxia, which are related to a GAA repeat expansion of the gene (FRDA) known as frataxin, are not observed in the rhesus monkey (Justice et al., 2001). However, the Korenberg laboratory’s work showing duplication of the Williams flanking regions in related monkey species suggests the potential for instability in rhesus monkeys. Moreover, there are other indications that rhesus monkeys do demonstrate other genetic variations that are closely associated with human social behavior. For example, Suomi’s laboratory has demonstrated that risk taking and aggressive social behavior is associated with one variant of the polymorphic serotonin transporter gene (Suomi, in press).
Once we have identified naturally occurring hyposocial and hypersocial populations of animals, subsets will be recruited into studies of social behavior using testing such as dyadic social interactions, differentiation of facial expressions, discrimination of angle of gaze etc. that will also be used in the analysis of Williams subjects. The results of these studies of social behavior will then be used to design the appropriate genetic analyses within families, to both determine inheritance and ultimately create links to other genomic regions. It is expected that sequencing of the rhesus monkey will be complete by the latter part of the grant period and will coincide with the results of the broader behavioral analyses of the rhesus cohorts. This will provide an excellent convergence of genetic and behavioral information which will position us to be abl to formulate the most powerful approaches to linking genes with behavior in the rhesus monkey.
Thus, the specific aim of Project 3 is to determine whether a Williams-like deletion occurs in nonhuman primates and produces a hypersocial monkey. Behavioral assays will be used to narrow candidate animals for genetic analysis. We will also map the Williams region in the rhesus monkey. Finally, candidate animals will also be screened for other genetic variants that may correlate with their increased or decreased social behavior.
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