Telomeric profiles and telomerase activity in turkey satellite cell clones with different in vitro growth characteristics

Telomerase gene expression in the chicken: Telomerase RNA (TR) and reverse transcriptase (TERT) transcript profiles are tissue-specific and correlate with telomerase activity

Telomerase is the specialized enzyme which replicates the telomeres, thus maintaining the integrity of the chromosome ends; in absence of enzyme activity telomere lengths decrease, ultimately impacting genome stability. In this study, we examined the mRNA expression of both enzyme components, the RNA template (TR) and catalytic subunit (TERT) during growth and development of the chicken to better understand mechanisms which regulate telomerase activity in vertebrates. Quantitative real-time PCR was used to establish transcript profiles for six ages ranging from pre-blastula to two-year old adults. Organ-specific profiles were established for brain, heart, liver, intestine, spleen and gonad. The pre-blastula and gastrula stages exhibited very high transcript levels of both telomerase components; organs from the embryos and adult showed transcript levels either similar or down-regulated relative to the early differentiation embryo stages. Organs which are known to become negative for telomerase activity between the embryo and adult stages (brain, heart, liver) exhibited down-regulation of TR and either no change or an increase in TERT transcripts. Whereas, organs which maintain high telomerase activity even in adults (intestine, spleen, gonad), generally exhibited up-regulation of transcripts for both components. However, there were some tissue-specific differences between telomerase-positive tissues. These results show that TERT and TR transcript levels correlate with telomerase activity profiles and suggest that TR is the rate-limiting component in telomerase-negative tissues.

Telomeres in the chicken: genome stability and chromosome ends

Telomeres are the complex nucleoprotein structures at the termini of linear chromosomes. Telomeric DNA consists of a highly conserved hexanucleotide arranged in tandem repeats. Telomerase, a ribonucleoprotein of the reverse transcriptase family, specifies the sequence of telomeric DNA and maintains telomere array length. Numerous studies in model organisms established the significance of telomere structure and function in regulating genome stability, cellular aging, and oncogenesis. Our overall research objectives are to understand the organization of the telomere arrays in chicken in the context of the unusual organization and specialized features of this higher vertebrate genome (which include a compact genome, numerous microchromosomes, and high recombination rate) and to elucidate the role telomeres play in genome stability impacting cell function and life span. Recent studies found that the chicken genome contains three overlapping size classes of telomere arrays that differ in location and age-related stability: Class I 0.5 to 10 kb, Class II 10 to 40 kb, and Class III 40 kb to 2 Mb. Some notable features of chicken telomere biology are that the chicken genome contains ten times more telomeric DNA than the human genome and the Class III telomere arrays are the largest described for any vertebrate species. In vivo, chicken telomeres (Class II) shorten in an age-related fashion and telomerase activity is high in early stage embryos and developing organs but down-regulates during late embryogenesis or postnatally in most somatic tissues. In vitro, chicken cells down-regulate telomerase activity unless transformed. Knowledge of chicken telomere biology contributes information relevant to present and future biotechnology applications of chickens in vivo and chicken cells in vitro.

Muscle stem cells

Since its discovery four decades ago, the satellite cell of skeletal muscle has been implicated as the major source of myogenic cells involved in growth and repair of muscle fibres. This review not only looks at the role of the satellite cell in these processes but discusses how cells derived from other sources and tissues have recently been implicated in muscle formation and regeneration. Muscle itself also yields cells that contribute to other cell lineages although it is currently debated as to whether these cells originate within muscle or have migrated there from other tissues. The reality of using cells from muscle or other tissues to repair diseased muscle fibres is also addressed.