Telomere length indicated as terminal restriction fragments (TRFs) by Southern blot analysis. (A) Distribution of telomere length as TRFs of various pig cell types. Each lane shows the intensity of TRF from different samples. At last 30 grids were scanned for each sample. Take HEF for example, “Intensity” indicates the scanned intensity of each grid. The Intensity in red and blue rectangle was used as threshold of the upper and lower background, and values above them for calculation of telomere length as detailed in Methods. FF and FM, fetal fibroblast and mesenchymal cells derived from embryonic day 50, respectively; NF and NM, newborn (7 or 8 days after birth) fibroblast and mesenchymal cells, respectively; AF, adult fibroblast from the ear skin of an adult pig, 3–4 months after birth; P, passage. (B) Average telomere lengths shown as TRFs in kilobase (kb) pairs of different cell types and changes in telomere lengths during passages. HEF, human embryonic fibroblasts. The data (mean±S.E.) was averaged from three independent experiments. *, p < 0.05; **, p < 0.01, compared to the earliest passage of the same cell types, by ANOVA analysis using Statview software. (C) Schematic representation of terminal restriction sites for digestion by enzyme combinations HinfI and RsaI.