Somatic deletion events occur during early embryonic development and modify the extent of CAG expansion in subsequent generations

• Published in: Human molecular genetics 2004-12, Vol.13 (24), p.3057-3068
• Main Authors: Kovtun, I.V., Thornhill, A.R., McMurray, C.T.
• Format: Article
• Language: English
• Subjects: Animals; Base Sequence; Biological and medical sciences; Cell differentiation, maturation, development, hematopoiesis; Cell physiology; Chromosome aberrations; DNA Repair - physiology; DNA-Binding Proteins - metabolism; Embryo, Mammalian - metabolism; Female; Fundamental and applied biological sciences. Psychology; Genetics of eukaryotes. Biological and molecular evolution; Humans; Huntington Disease - genetics; Male; Medical genetics; Medical sciences; Mice; Mice, Transgenic; Molecular and cellular biology; MutS Homolog 2 Protein; Pedigree; Proto-Oncogene Proteins - metabolism; Sequence Deletion; Trinucleotide Repeat Expansion
• ISSN: 0964-6906; 1460-2083
• DOI: 10.1093/hmg/ddh325

Alterations in trinucleotide repeat length during transmission are important in the pathophysiology of Huntington's disease (HD). However, it is not well understood where, when and by what mechanism expansion occurs. We have followed the fate of CAG repeats during development in mice that can [hHD(−/+)/Msh2(+/+)] or cannot [hHD(−/+)/Msh2(−/−)] expand their repeats. Here we show that long repeats are shortened during somatic replication early in the embryo of the progeny. Our data point to different mechanisms for expansion and deletion. Deletions arise during replication, do not depend on the presence of Msh2 and are largely restricted to early development. In contrast, expansions depend on strand break repair, require the presence of Msh2 and occur later in development. Overall, these results suggest that deletions in early development serve as a safeguard of the genome and protect against expansion of the disease-range repeats during transmission.