Postnatal Survival of Mice with Maternal Duplication of Distal Chromosome 7 Induced by a Igf2/H19 Imprinting Control Region Lacking Insulator Function

Li Han,Piroska E Szabó,Jeffrey R Mann,Anne C Ferguson-Smith

doi:10.1371/journal.pgen.1000803

Abstract

The misexpressed imprinted genes causing developmental failure of mouse parthenogenones are poorly defined. To obtain further insight, we investigated misexpressions that could cause the pronounced growth deficiency and death of fetuses with maternal duplication of distal chromosome (Chr) 7 (MatDup.dist7). Their small size could involve inactivity of Igf2, encoding a growth factor, with some contribution by over-expression of Cdkn1c, encoding a negative growth regulator. Mice lacking Igf2 expression are usually viable, and MatDup.dist7 death has been attributed to the misexpression of Cdkn1c or other imprinted genes. To examine the role of misexpressions determined by two maternal copies of the Igf2/H19 imprinting control region (ICR)—a chromatin insulator, we introduced a mutant ICR (ICRΔ) into MatDup.dist7 fetuses. This activated Igf2, with correction of H19 expression and other imprinted transcripts expected. Substantial growth enhancement and full postnatal viability was obtained, demonstrating that the aberrant MatDup.dist7 phenotype is highly dependent on the presence of two unmethylated maternal Igf2/H19 ICRs. Activation of Igf2 is likely the predominant correction that rescued growth and viability. Further experiments involved the introduction of a null allele of Cdkn1c to alleviate its over-expression. Results were not consistent with the possibility that this misexpression alone, or in combination with Igf2 inactivity, mediates MatDup.dist7 death. Rather, a network of misexpressions derived from dist7 is probably involved. Our results are consistent with the idea that reduced expression of IGF2 plays a role in the aetiology of the human imprinting-related growth-deficit disorder, Silver-Russell syndrome.

Highlights

Parthenogenetic mouse embryos usually die before 6K days post coitum
To gain further insight into which misexpressions might be involved, we examined some of the misexpressions that could determine the small size and fetal death of a ‘‘partial parthenogenone’’—embryos with maternal duplication of distal Chr 7 (MatDup.dist7)
We investigated the involvement of two maternal copies of the insulin like growth factor 2’ (Igf2)/H19 imprinting control region (ICR), which is associated with lack of activity of the Igf2 gene, encoding a growth factor, and over-activity of H19

Summary

Introduction

Parthenogenetic mouse embryos usually die before 6K days post coitum (dpc). Occasionally they develop to the 25 somite forelimb bud stage or approximately 9K dpc [1,2,3,4,5]. To better define the causes of failed parthenogenetic development, and learn more of how imprinted genes at dist work together to regulate normal development, we have examined some of the misexpressions of imprinted genes thought to contribute to the abnormal development of MatDup.dist conceptuses. These display a pronounced growth deficit of the fetus and placenta and die at the late fetal stage, or possibly at birth.

Methods

Results

Discussion

Conclusion