The hard clam genome reveals massive expansion and diversification of inhibitors of apoptosis in Bivalvia

BACKGROUND

Inhibitors of apoptosis (IAPs) are critical regulators of programmed cell death that are essential for development, oncogenesis, and immune and stress responses. However, available knowledge regarding IAP is largely biased toward humans and model species, while the distribution, function, and evolutionary novelties of this gene family remain poorly understood in many taxa, including Mollusca, the second most speciose phylum of Metazoa.

RESULTS

Here, we present a chromosome-level genome assembly of an economically significant bivalve, the hard clam Mercenaria mercenaria, which reveals an unexpected and dramatic expansion of the IAP gene family to 159 members, the largest IAP gene repertoire observed in any metazoan. Comparative genome analysis reveals that this massive expansion is characteristic of bivalves more generally. Reconstruction of the evolutionary history of molluscan IAP genes indicates that most originated in early metazoans and greatly expanded in Bivalvia through both lineage-specific tandem duplication and retroposition, with 37.1% of hard clam IAPs located on a single chromosome. The expanded IAPs have been subjected to frequent domain shuffling, which has in turn shaped their architectural diversity. Further, we observed that extant IAPs exhibit dynamic and orchestrated expression patterns among tissues and in response to different environmental stressors.

CONCLUSIONS

Our results suggest that sophisticated regulation of apoptosis enabled by the massive expansion and diversification of IAPs has been crucial for the evolutionary success of hard clam and other molluscan lineages, allowing them to cope with local environmental stresses. This study broadens our understanding of IAP proteins and expression diversity and provides novel resources for studying molluscan biology and IAP function and evolution.

Expression of Inhibitor of Apoptosis Gene Family Members in Bladder Cancer Tissues and the 5637 Tumor Cell Line

Background: Apoptosis is suppressed in cancer tissues and tumor cell lines because anti-apoptosis genes are overexpressed. The inhibitor of apoptosis proteins (IAP) gene family contributes to control of apoptosis. The expression profile of eight genes of the IAP family in biopsies from patients with a history of bladder cancer and normal bladder tissues, as well as a bladder tumor cell line (5637), was assessed in the present study. Methods: Cancer tissue samples were obtained at surgery and the 5637 tumor cell line was cultured in RPMI1640 medium. Beyond tumor margins were selected as normal tissue. Expressional profile of interested genes was obtained by using specific primers and the real-time PCR method. Results: The results showed that expression of seven of the studied genes was up-regulated in cancer tissues and the cell line whereas BIRC4 (XIAP) was down-regulated in both. Conclusions: The results showed that these genes were expressed to a greater extent in cancer tissue and cancer cells than in normal tissues. The data suggested that over-expression of anti-apoptotic genes such as IAP family members, can trigger cells to escape from apoptosis.