Nuclear phenotypic changes in cells originating from migrating tenocytes in tendon explants

Tenocytes migrating from cultured rat tendon explants aggregate and gradually align in parallel rows with the tendons long axis as the explant period extends up to 12 days and collagen bundles become structurally remodeled. Tendon architecture and mechanical load are known to affect fibroblast phenotypes; thus, we studied cell cultures derived from tenocytes at early and later migration stages using image analysis and immunofluorescence for selected epigenetic markers to identify differences in nuclear characteristics across migration periods. Feulgen-DNA amounts and global DNA 5-methylcytosine and acetylated H3K9 distribution were not found to differ in the cells originating from tenocytes that migrated at the 8- and 12-day periods of tendon culture. However, light absorbance, fractal dimension, and margination features related to chromatin condensation and distribution in the Feulgen-stained cell nuclei differed during these periods. Accumulation of the H3K4me2 marker at the nuclear periphery in cells obtained after a longer explant culture period, when the margination feature reaches larger values, may represent the acquisition of an enhanced transcriptional memory that could affect future gene expression levels. Further assays are required to determine whether the present image analysis results correlate with the differential potential of these cells for extracellular matrix synthesis and practical bioengineering purposes.