Next, we investigated whether this chromosome damage was exacerbated by exposure to ethanol. As a control, we exposed wild-type or Fancd2−/− mice to mitomycin C (Extended Data Fig. 1d). The experimental scheme (outlined in Fig. 2f) shows how we determined the prevalence of micronuclei in reticulocytes and aberrant metaphases following exposure to ethanol. A single dose of ethanol caused a marked increase in the proportion of reticulocytes containing micronuclei in Aldh2−/− mice. Notably, this induction was comparable to that observed in wild-type mice following exposure to agents known to induce genome instability, such as ionizing irradiation or vincristine (Extended Data Fig. 1e). However, there was a stronger induction of micronucleus formation in Aldh2−/−Fancd2−/− mice than in controls (Fig. 2g), which was accompanied by a striking increase in the number of abnormal metaphases, with almost 60% of metaphases having damaged chromosomes following ethanol exposure (Fig. 2h, Extended Data Fig. 1g–i). These mice rapidly lost the ability to produce blood and died from bone-marrow failure (Extended Data Fig. 2). These results show that, despite activation of homologous recombination, the Fanconi anaemia crosslink-repair pathway is essential for preventing chromosome breakage and loss of blood homeostasis in response to aldehydes.
