Ontogeny of telomerase in chicken: Impact of downregulation on pre- and postnatal telomere length in vivo

Telomeres are the termini of linear chromosomes composed of tandem repeats of a conserved DNA sequence. Telomerase provides a mechanism for proliferat ing cells to offset telomeric sequence erosion by synthesizing new repeats onto the end of each parental DNA strand. Reduced or absent telomerase acti vity can lead to telomere shortening and genome instability. Telomeres and telomerase have not previously been characterized during ontogeny of any av ian species. In the present study, telomerase activity in the chicken model was examined from early differentiation embryos through to adulthood. Telo merase activity was detected in all early embryos (preblastula through neur ula) and in tissues throughout organogenesis. Subsequently, telomerase was downregulated in the majority of somatic tissues, either pre- or postnatall y. A subset of tissues, such as intestine, immune and reproductive organs, exhibited constitutive activity. The impact of telomerase downregulation on telomere length was investigated and a telomere reduction of 3.2 kb in som atic tissues compared with germ line was observed in 5-year-old adults. The present results suggest that the telomere clock function is a conserved fe ature of avians as well as mammals. Knowledge regarding the relationships a mong telomerase regulation, proliferation/senescence profiles and different iation status will be useful for numerous applications of chicken cells.