Abstract

Telomeres are specialized nucleoprotein complexes at the termini of linear chromosomes that are composed of TTAGGG sequences in vertebrates. Telomere lengths in animals vary with species, age, tissue types, environment, and cloning. The experiment conducted emphasized the amount of telomeric DNA in the lymphocytes and organs of growing cloned cattle and their second and third generations. Using somatic cell nuclear transfer (SCNT), 16 cloned (Generation, clone G1) Korean Native cows were obtained from ear skin fibroblasts and 2 cloned bulls from fetal fibroblasts. In addition, 3 females and 2 males (clone G2) were produced from each cloned cow by artificial insemination (AI). A third generation calf (clone G3) was derived from clone G2 by AI. The lymphocytes of all cloned cattle (G1), their offspring (G2), and age-matched controls were examined 3 times at 6-month intervals whereas G3 was examined only once. The amount of telomeric DNA was analyzed by quantitative fluorescence in situ hybridization (Q-FISH) with a human telomeric DNA repeat probe. A minimum of 100 interphase nuclei from each set of harvests was studied to determine the mean and medium percentages of telomeric DNA using MetaMorph Imaging System (Universal Imaging Co, West Chester, PA, USA). The amounts of telomeric DNA in cloned cattle from both ear skin fibroblasts (female, n = 16) and fetal fibroblasts (male, n = 2) were less than those of age-matched controls (P < 0.01). Additionally, irrespective of gender, the telomeres in the clone G2 and G3 calves were lower than in controls (n = 6; P < 0.05). Furthermore, in the cloned cattle, the amount of telomeric DNA was drastically less than that of control animals during growth. Moreover, we examined the internal organs and tissues of a cloned cow at 30 months. The telomeres of leukocytes, cerebrum, spleen, cerebellum, hindbrain, and lung were a little smaller, whereas those of the liver, pituitary, kidney, and heart were slightly larger, than those of an age-matched cow. The results showed a remarkable difference in the amount of telomeric DNA between SCNT cloned cattle and normal cattle. Although the organs and tissues were not correlated, the amount of telomeres rapidly decreased with growth in cloned cattle. Conclusively, the telomeres of a cloned animal and its calves were significantly shorter than those of control cattle, and the short telomeres in calves could be inherited by progeny from their cloned mother.