Research article

Genetic mapping of putative Chrna7 and Luzp2 neuronal transcriptional enhancers due to impact of a transgene-insertion and 6.8 Mb deletion in a mouse model of Prader-Willi and Angelman syndromes

Mihaela Stefan^1,7 , Kathryn C Claiborn¹ , Edyta Stasiek³ , Jing-Hua Chai¹ , Tohru Ohta^1,6 , Richard Longnecker⁴ , John M Greally³ and Robert D Nicholls^1,2,5,7

¹  Center for Neurobiology and Behavior, Department of Psychiatry, University of Pennsylvania, Philadelphia, PA 19104, USA

²  Department of Genetics, University of Pennsylvania, Philadelphia, PA 19104, USA

³  Division of Hematology, Department of Medicine, Albert Einstein College of Medicine, The Bronx, USA

⁴  Department of Microbiology and Immunology, Feinberg School of Medicine, Northwestern University, Ward 6-231, 303 East Chicago Ave, Chicago, IL 60611, USA

⁵  Birth Defects Laboratories, Children's Hospital of Pittsburgh, Room 2109 Rangos Research Center, 3460 Fifth Avenue, Pittsburgh, PA 15213, USA

⁶  Health Science University of Hokkaido, Hokkaido, Japan

⁷  Department of Pediatrics, Children's Hospital of Pittsburgh, 3460 Fifth Avenue, Pittsburgh, PA 15213

author email corresponding author email

BMC Genomics 2005, 6:157doi:10.1186/1471-2164-6-157

Published:	9 November 2005

Abstract

Background

Prader-Willi and Angelman syndrome (PWS and AS) patients typically have an ~5 Mb deletion of human chromosome 15q11-q13, of opposite parental origin. A mouse model of PWS and AS has a transgenic insertion-deletion (TgPWS/TgAS) of chromosome 7B/C subsequent to paternal or maternal inheritance, respectively. In this study, we define the deletion endpoints and examine the impact on expression of flanking genes.

Results

Using molecular and cytological methods we demonstrate that 13 imprinted and 11 non-imprinted genes are included in the TgPWS/TgAS deletion. Normal expression levels were found in TgPWS brain for genes extending 9.1- or 5.6-Mb centromeric or telomeric of the deletion, respectively. Our molecular cytological studies map the proximal deletion breakpoint between the Luzp2 and Siglec-H loci, and we show that overall mRNA levels of Luzp2 in TgPWS and TgAS brain are significantly reduced by 17%. Intriguingly, 5' Chrna7 shows 1.7-fold decreased levels in TgPWS and TgAS brain whereas there is a ≥15-fold increase in expression in neonatal liver and spleen of these mouse models. By isolating a Chrna7-Tg fusion transcript from TgAS mice, we mapped the telomeric deletion breakpoint in Chrna7 intron 4.

Conclusion

Based on the extent of the deletion, TgPWS/TgAS mice are models for PWS/AS class I deletions. Other than for the first gene promoters immediately outside the deletion, since genes extending 5.6–9.1 Mb away from each end of the deletion show normal expression levels in TgPWS brain, this indicates that the transgene array does not induce silencing and there are no additional linked rearrangements. Using gene expression, non-coding conserved sequence (NCCS) and synteny data, we have genetically mapped a putative Luzp2 neuronal enhancer responsible for ~33% of allelic transcriptional activity. The Chrna7 results are explained by hypothesizing loss of an essential neuronal transcriptional enhancer required for ~80% of allelic Chrna7 promoter activity, while the Chrna7 promoter is upregulated in B lymphocytes by the transgene immunoglobulin enhancer. The mapping of a putative Chrna7 neuronal enhancer inside the deletion has significant implications for understanding the transcriptional regulation of this schizophrenia-susceptibility candidate gene.