In quest of genomic treasure

Abstract

It should be emphasized that "129" is not simply a number but is also the designation of a mouse strain that has made a great contribution to modern biological science and technology. Embryonic stem cells derived from 129 mice were essential components of gene-targeting strategies in early research. More recently, 129 mice have provided superior donor genomes for cloning by nuclear transfer. Some factor or factors conferring genomic plasticity must exist in the 129 genome, but these remain unidentified.

Fig. 1.

The 129 strain consists of many substrains due to its complex history [4]. The image shows a commonly used 129/Sv mouse, which has the full designation, 129S1/Sv-p<+> Tyr<+>, indicating its substrain group (“129S” indicates a Steel substrain group) and coat color (wild type). This strain is available from the RIKEN BioResource Center (RBRC00002).

Fig. 2.

Principal component analysis for global gene expression profiles of blastocysts generated by ICSI (intracytoplasmic sperm injection) or SCNT (cumulus clone) with the B6D2F1 or 129 genotypes. Components 1 and 2 mean principal components with the first and second highest levels of variance, respectively. The percentages in parentheses indicate the contribution ratios of the components. Visualization of gene expression similarities clearly distinguished the B6D2F1 and 129 groups. SCNT-derived blastocysts from the B6D2F1 strain showed SCNT-specific expression profiles (enclosed with blue dotted lines), but those from 129 did not (enclosed with red dotted lines), indicating that the 129 genome was reprogrammed more correctly than the B6D2F1 genome by nuclear transfer.

Fig. 3.

The histology of a typical term placenta produced by SCNT. The image shows two- to three-fold enlargement (hyperplasia) with characteristic histology (upper). However, the presence of the 129 genome in the donor nucleus ameliorated the SCNT-associated placental abnormalities (lower). LB, labyrinth layer. TS, trophospongium layer. Bar = 5 mm.