Lynch syndrome (LS) is an autosomal dominant disorder, with high penetrance that affects approximately 3% of the cases of colorectal cancer. Affected individuals inherit germline mutations in genes responsible for DNA mismatch repair, mainly at MSH2, MLH1, MSH6 and PMS2. The molecular screening of these individuals is frequently costly and time consuming due to the large size of these genes. In addition, PMS2 mutation detection is often a challenge because there are 16 different pseudogenes identified until now. In the present work we evaluate a molecular screening strategy based in next generation sequencing (NGS) in order to optimize the mutation detection in LS patients. We established 16 multiplex PCRs for MSH2, MSH6 and MLH1 and 5 Long-Range PCRs for PMS2, coupled with NGS. The strategy was validated by screening 66 patients who filled Bethesda and Amsterdam criteria for LS from health institutions of Brazil. The mean depth of coverage for MSH2, MSH6, MLH1 and PMS2 genes was 7.988, 36.313, 11.899 and 4.772 times, respectively. Ninety-four variants were found in exons and flanking intron/exon regions for the four MMR genes. Twenty-five were pathogenic or VUS and found in 32 patients (7 in MSH2, 5 in MSH6, 12 in MLH1 e 1 in PMS2). All variants were confirmed by Sanger sequencing. The strategy was efficient to reduce time consuming and costs to identify genetic changes at these MMR genes, reducing in three times the number of PCR reactions performed per patient and was efficient in identifying variants at PMS2 gene.
The DNA Damage Response (DDR) is a complex network of biological processes that protect cells from accumulating aberrant DNA structures, thereby maintaining genomic stability and, as a consequence, preventing the development of cancer and other diseases. The DDR pathway is coordinated by a signaling cascade mediated by the PI3K-like kinases (PIKK) ATM and ATR and by their downstream kinases CHK2 and CHK1, respectively. Together, these kinases regulate several aspects of the cellular program in response to genomic stress. Much of our understanding of these kinases came from studies performed in the 1990s using yeast as a model organism. The purpose of this review is to present a historical perspective on the discovery of the DDR kinases in yeast and the importance of this model for the identification and functional understanding of their mammalian orthologues. Figure 1 -Timeline for the discovery of DDR kinases in yeast and human. Although the gene encoding S. pombe Chk1 was identified before Dun1, its kinase activity was associated with DDR only in 1996 (Walworth and Bernards, 1996).
Saccharomyces cerevisiae
exhibits gene expression homeostasis, which is defined as the buffering of transcription levels against changes in DNA copy number during the S phase of the cell cycle. It has been suggested that
S. cerevisiae
employs an active mechanism to maintain gene expression homeostasis through Rtt109-Asf1-dependent acetylation of histone H3 on lysine 56 (H3K56). Here, we show that gene expression homeostasis can be achieved independently of H3K56 acetylation by Tos4 (
T
arget
o
f
S
wi6-
4
). Using Nanostring technology, we establish that Tos4-dependent gene expression homeostasis depends on its forkhead-associated (FHA) domain, which is a phosphopeptide recognition domain required to bind histone deacetylases (HDACs). We demonstrate that the mechanism of Tos4-dependent gene expression homeostasis requires its interaction with the Rpd3L HDAC complex. However, this is independent of Rpd3’s well-established roles in both histone deacetylation and controlling the DNA replication timing program, as established by deep sequencing of Fluorescence-Activated Cell Sorted (FACS) S and G2 phase populations. Overall, our data reveals that Tos4 mediates gene expression homeostasis through its FHA domain-dependent interaction with the Rpd3L complex, which is independent of H3K56ac.
Screening for CALR mutations is essential in BCR-ABL-negative MPNs since it not only provides valuable diagnostic and prognostic information but also identifies potential treatment targets. Since this study describes the importance of screening for known and novel biomarkers, we described in detail three methods that could be easily integrated into a clinical laboratory.
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