Hierarchical cluster analyses and heat map analyses of silkworm tissues using R-statistics

Proteins from silkworm (Bombyx mori L.) silk glands, fat bodies, and hemolymph were analyzed by matrix assisted laser desorption ionization time-of-flight mass spectrometry using sinapinic acid as a matrix. Peak percentages were calculated for each peak from m/z 2,000 to m/z 20,000 against the sum of all observed peak intensities; hierarchical cluster analysis and heat map analysis were performed using R-statistics software. For the silk glands, clusters obtained from MALDI-TOF-MS analysis were consistented with the morphological classification. Hierarchical clustering using MALDI-TOF-MS data was considered applicable to the small and sequential biopsies. In hemolymph, obvious clusters were observed from the anterior part to posterior part, and the proteins in hemolymph were not considered homogeneous throughout the body. While the clusters obtained from fat body analysis were weaker than those of silk glands and hemolymph, three clusters were observed. Based on the protein profile, fat bodies were also considered as differentiated tissue.