Cytokinesis failure and attenuation: new findings in Fanconi anemia

Abstract

The hallmarks of the rare inherited disorder Fanconi anemia (FA) are progressive bone marrow failure and susceptibility to cancer. The former is the major cause of death for patients with FA, as it usually occurs earlier in life than cancer development. Despite spectacular advances in unraveling the molecular details of FA, the origin of the bone marrow failure that is central to this condition for most patients has long been puzzling and controversial. Two studies recently published in the JCI, including one in this issue, will add to the debate. They also highlight the fact that studying rare disorders can elucidate important new clinical and biological principles.

Figure 1. Cytokinesis failure in FA.

PICH-BLM UFBs are ultrafine DNA bridges that have FANCD2-FANCI foci at their extremities and are most likely derived from unresolved replication intermediates. The paper by Vinciguerra et al. (7) shows that hematopoietic cells from patients with FA have an increased number of UFBs between daughter nuclei that may inhibit cytokinesis, leading to binucleated or multinucleated cells. These cells may undergo apoptosis, contributing to BMF, or may lead to genomic instability and malignancy.

Figure 2. Clonal attenuation of a G₂ checkpoint in FA.

Hematopoietic cells from patients with FA exhibit slow growth and accumulate in G₂, leading to BMF. Ceccaldi et al. (8) show that, in some patients, blood counts are normalized due to the appearance of a clone of cells, in which the arrest at the G₂ checkpoint does not take place. Hematopoiesis in these patients is greatly improved, but the trade off is an increased susceptibility to later development of MDS and AML. This scenario, identified in FA, is likely to be a theme, applicable not only to many forms of inherited BMF syndromes but possibly to other regenerative disorders associated with an increased risk of malignant transformation.