The versatility and utility of the domestic chicken as a developmental model was recently celebrated in a special issue of the journal Developmental Dynamics [(2004) 229, 413-712.] The chicken is one of the primary models for vertebrate developmental biology and a model organism for the study of virology, immunology, cancer and gene regulation (Tickle, 2004; Antin and Konieczka, 2005). With a 6.6X draft sequence of its genome completed, the chicken is poised to become even more valuable in traditional fields of study and also in aging research.
The earliest recorded descriptions of the chicken as a model for biological processes are attributed to Hippocrates and Aristotle who both wrote about embryonic development in fertilized chicken eggs. Twentieth century embryologists authored numerous treatises describing, diagramming, and providing detailed photographs of the chicken during development (Hamburger and Hamilton, 1951; Romanoff, 1960; Eyal-Giladi and Kochev, 1976) which promoted use of the chicken embryo as a model for study of mechanisms including morphogenesis; neurogenesis; somatogenesis; limb, limb-digit and craniofacial development; left-right symmetry; axis development and others. The extensive use of the chicken as a model for early vertebrate development and its role in biomedical research has of necessity produced a detailed and comprehensive body of knowledge about basic chicken biology (Stern, 2005; Scanes et al., 2004). Add to all of this the accessibility of the chicken embryo, the relative economy of breeding and maintaining chickens and the ease of manipulation of embryonic and adult tissues and the chicken becomes an obvious choice as a model for the study of organismal and cellular senescence.
Telomere-binding proteins, their interaction partners and transcription factors play a prominent role in telomere maintenance and telomerase activation. We examined mRNA expression levels of tankyrase 1 and 2, TRF1 and 2, c-myc, TERT and TR in Gallus domesticus, the domestic chicken, by quantitative real-time PCR, establishing expression profiles for three contrasting cell systems: the pluripotent gastrula, differentiated embryo fibroblasts and transformed DT40 cells.
This study examined telomerase activity and gene expression profiles for three genes in Gallus gallus domesticus: telomerase reverse transcriptase (chTERT), telomerase RNA (chTR), and c-myc. Expression of these genes was studied in chicken embryonic stem (chES) cells, chicken embryo fibroblasts (CEFs), and DT40 cells using quantitative real-time polymerase chain reaction. Our results establish that, relative to transcription levels in telomerase-negative CEFs, chTERT and chTR are up-regulated in telomerase-positive chES cells. Transcription levels of chTERT, chTR, and c-myc are dramatically up-regulated in telomerase-positive DT40 cells, relative to CEFs and chES cells. These results are consistent with a model in which telomerase activity is up-regulated in proliferating embryonic stem cells requiring stable telomeres to endure multiple rounds of cell division; down-regulated in differentiated, lifespan-limited cells; and dramatically up-regulated in immortalized, transformed cells for which uncontrolled proliferation is correlated with c-myc dysregulation and telomerase activity.
ABSTRACT 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.
Delany, Daniels, Swanberg and Taylor 2003, Poultry Science