Functional differences between parental genomes are due to differential expression of parental alleles of imprinted genes. Neuronatin (Nnat) is a recently identified paternally expressed imprinted gene that is initially expressed in the rhombomeres and pituitary gland and later more widely in the central and peripheral nervous system mainly in postmitotic and differentiating neuroepithelial cells. Nnat maps to distal chromosome (Chr) 2., which contains an imprinting region that causes morphological abnormalities and early neonatal lethality. More detailed mapping analysis of Nnat showed that it is located between the T26H and T2Wa translocation breakpoints which is, surprisingly, proximal to the reported imprinting region between the T2Wa and T28H translocation breakpoints, suggesting that there may be two distinct imprinting regions on distal chromosome 2. To investigate the potential role of Nnat, we compared normal embryos with those which were PatDp.dist2.T26H (paternal duplication/maternal deficiency of chromosome 2 distal to the translocation breakpoint T26H) and MatDp.dist2.T26H. Expression of Nnat was detected in the PatDp.dist2.T26H embryos, where both copies of Nnat are paternally inherited, and normal embryos but no expression was detected in the MatDp.dist2.T26H embryos with the two maternally inherited copies. The differential expression of Nnat was supported by DNA methylation analysis with the paternally inherited alleles being unmethylated and the maternal alleles fully methylated. Although experimental embryos appeared grossly similar phenotypically in the structures where expression of Nnat was detected, differences in folding of the cerebellum were observed in neonates, and other more subtle developmental or behavioral effects due to gain or loss of Nnat cannot be ruled out.
Bibliographical noteFunding Information:
We thank F. Ishino for valuable information and materials prior to publication and all the members of our laboratories for their help and advice. We are especially grateful to W. Rideout III for help with molecular studies; K. J. Hilton for preparation of embryos; M. Narasimha for help with in situ hybridization; S. Aparicio and E. B. Keverne for useful suggestions, the histology department at MRC for sections; L. Cobb for advice on histological sections; K. M. S. Townsend for assistance with analysis of FISH results, H. J. Miller and S. F. Wroe for Nnat and Hprt primers, respectively; K. Glover for photographs; and D. Brooker for looking after the mice. This work was supported by the Wellcome Trust (Grant 036481), the International Human Frontier Science Program Organization (Grant RG-516/94M), and the Medical Research Council. N.K. has a postdoctoral fellowship from the Sankyo Foundation of Life Science and is also supported by the Nakayama Foundation for Human Science and the Daiwa Anglo±Japanese Foundation. The animal studies described in this paper were carried out under the guidance issued by the Medical Research Council in ``Responsibility in the Use of Animals for Medical Research'' (July 1993) and Home Of®ce Project Licence No. 30/00875.