Loss of the histone chaperone ASF1B reduces female reproductive capacity in mice.

Anti-silencing function 1 (ASF1) is an evolutionarily conserved histone H3-H4 chaperone involved in the assembly/disassembly of nucleosome and histone modification. Two paralogous genes, Asf1a and Asf1b, exist in the mouse genome. Asf1a is ubiquitously expressed and its loss causes embryonic lethality. Conversely, Asf1b expression is more restricted and has been less studied. To determine the in vivo function of Asf1b, we generated a Asf1b-deficient mouse line (Asf1b(GT(ROSA-ßgeo)437)) in which expression of the lacZ reporter gene is driven by the Asf1b promoter. Analysis of ß-galactosidase activity at early embryonic stages indicated a correlation between Asf1b expression and cell differentiation potential. In the gonads of both male and female, Asf1b expression was specifically detected in the germ cell lineage with a peak expression correlated with meiosis. The viability of Asf1b-null mice suggests that Asf1b is dispensable for mouse development. However, these mice showed reduced reproductive capacity compared with wild-type controls. We present evidence that the timing of meiotic entry and the subsequent gonad development are affected more severely in Asf1b-null female mice than in male mice. In female mice, in addition to subfertility related to altered gamete formation, variable defects compromising the development and/or survival of their offspring were also observed. Altogether, our data indicate the importance of Asf1b expression at the time of meiotic entry, suggesting that chromatin modifications may play a central role in this process.

Loss of heterozygosity, allele silencing and decreased expression of p73 gene in breast cancers: prevalence of alterations in inflammatory breast cancers.

The p73 gene is a p53 homologue located at 1p36-33, a region submitted to deletions in breast cancer (BC) and putatively imprinted. To study whether p73 was associated with breast carcinogenesis, loss of heterozygosity (LOH), allele expression and transcript levels were assessed in 59 BC, including 39 BC presenting no inflammatory symptoms (NBC) and 20 inflammatory BC (IBC). IBC is a rare but aggressive form of cancer with a very poor prognosis. Normal breast epithelium (BE) and lymphocytes from patients were used as controls. StyI polymorphism generating GC and/or AT alleles was used to select 22 heterozygous patients. p73 LOH was significantly higher in IBC than in NBC [five of eight cases (62%) versus two of 14 cases (14%); Fisher's exact test, P=0.05]. p73 was biallelically expressed in all BE. In contrast, 12 of 16 (75%) BC were monoallelically expressed, showing that allele silencing was significantly associated with breast carcinogenesis (P=0.012), AT being the preferential silent allele (10 out of 12 tumours). p73 mRNA levels in NBC and IBC were two- and threefold lower than in BE, respectively, suggesting that decreased expression could be related to tumour aggressiveness. In conclusion, LOH, allele silencing and decreased expression of the p73 gene may play a role in breast carcinogenesis.