The influence of triploidy on gene expression in the silkworm, bombyx mori

In Bombyx mori, it is well established that polyploids are easily induced when newly laid eggs are exposed to a variety of conditions, such as high or low temperature, centrifugal force, or chemicals like colchicine. To investigate gene dosage effects by varying the ploidy, the transcription levels of six genes expressed in various tissues were analysed in the diploid and two different genetically produced triploids (PPC and CCP). In the PPC triploid, the transcription level per cell of two genes was directly proportional to the structural gene dosage, whereas two other genes showed the mRNA level expected if compensation occurred. In the CCP triploid, three genes displayed dose-dependent levels of expression, whereas one gene showed the same expression level as the diploid strains. In both triploids, exceptional cases showed a negative correlation of expression with ploidy or a positive correlation greater than expected from the structural gene dosage. Interestingly, the transcription levels of most tested genes were significantly different from the strains which were used as parents of the triploids, and also widely divergent expression patterns were found for some genes in the diploid offspring. In this study, the cause of the unexpected expression patterns observed in the euploid series is discussed in relation to the difference between the two parental strains in expression level of genes and in trans-acting regulatory effects on their target genes.