Gene Expression Analysis of Ruditapes philippinarum Haemocytes after Experimental Perkinsus olseni Zoospore Challenge and Infection in the Wild

The production of Manila clam (Ruditapes philippinarum) is seriously threatened by the protistan parasite Perkinsus olseni. We characterized and compared gene expression of Manila clam haemocytes in response to P. olseni in a time-course (10 h, 24 h, 8 d) controlled laboratory challenge (LC), representing the first steps of infection, and in a more complex infection in the wild (WI) using a validated oligo-microarray containing 11,232 mostly annotated transcripts. Several immune-genes involved in NIK/NF-kappaB signalling, toll-like receptor signalling and apoptosis were activated at LC-10 h. However, down-regulation of others like lysozyme, histones, cathepsins and heat shock proteins indicated signals of immunodepression, which appeared exacerbated at LC-24 h, where only down-regulated genes were detected. A rebound of haemocytes activity occurred at LC-8 d as shown by up-regulation of genes involved in cytoskeleton organization and cell survival. WI showed a more complex picture and several immune-relevant processes, including cytoskeleton organization, cell survival, apoptosis, encapsulation, cell redox- and lipid- homeostasis were activated, involving the main mechanism of host response. Our results provide useful information, including potential biomarkers, to develop strategies for controlling Manila clam perkinsosis. Gene expression in Manila clams haemocytes naturally infected by P. olseni in a natural bed (wild infection, WI) and after a laboratory challenge (LC) at 10 hours, 24 hours and 8 days after the onset of challenge was measured. A total of 16 microarrays were used in the experiments: i) 4 for the WI samples, one control (pool of three different replicates) and three biological replicates for the infected haemocytes; and ii) 12 for the LC samples along the 3 time series: 1 control (pool of three different replicates) and 3 biological replicates at each time.