Studies of Chromosome 22 in Major Psychosis
The epigenetics project in our laboratory started in late 1980s with Mellissa (Wigle) Mann (M.Sc. 1990), who used the technology of the day to establish that the same genes being passed on from maternal vs. paternal lineages had different methylation specificities. Southern blot results using Msp I and Hpa II identified parent of origin effects, however they lacked specificity in the absence of the mouse genome sequence. Subsequently, this project was taken up by Debora Mancini (Ph.D. 1999) involving a set of tumor suppressor (TS) genes. Employing sodium bisulfite modification of genomic DNA, she identified specific sequences in the promoters of NF1, Rb and BRCA1 genes that were differently methylated. This methylation played an important role in transcriptional regulation by interfering with specific transcription factors. Further she identified that the aberrant methylation represented the second hit in the two hit hypothesis of tumorogenesis in a number of tumors (Mancini et al., 1997, 1998, 1999). Also, at about the same time, Indira Pillay (M.Sc. 1996) demonstrated tissue specific methylation for a number of genes during mouse development. These studies gave us an appreciation for the role of epigenetic modifications, particularly DNA methylation in the development of abnormalities. To us it represented the most logical hypothesis for the explanation of familial and population patterns in a number of complex multifactorial diseases including schizophrenia (O’Reilly and Singh 1996; Deb-Rinker et al., 1999, 2002; Singh et al., 2002, 2002, 2003, 2004; McDonald et al., 2004; Murphy et al., 2005).
Methylation was then examined in the specific context of schizophrenia using the representational difference analysis (RDA) technique to identify differences, including epigenetic differences between monozygotic twins discordant for schizophrenia. Tim Klempan (M.Sc. 1998) and Paromita Deb-Rinker (Ph.D. 2000) identified retroviral like sequences which differed between discordant twins (Deb-Rinker et al., 1999, 2002) while analyses on other discordant twin pairs yielded no differences (McDonald et al., 2003).
Research on the genetic basis of schizophrenia continues in the lab today with Brenda Murphy and Patrick McDonald using the sodium bisulfite DNA modification technique to analyze the promoter region of several candidate genes. The focus is currently on candidate genes from the 22q11 region and chromosome 6. Here the methylation status of cytosines in the promoter region of these genes is being determined, and their relation to gene expression established. Both blood and brain based studies are producing interesting results on the methylation and expression patterns of these candidate genes.