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When you learn that deer antlers have been subjected to proteome analysis, you may think that this is simply a case of choosing a species that has not been covered and giving it the proteome treatment. But antler is the only tissue from all mammals that is regenerated annually, so it is hoped to discover the molecular basis behind this remarkable system. Deer antlers have important functions. Historically, the stags developed antlers as a weapon to defend against their natural enemies such as bear, wolf, mountain lion and lynx. In some countries, the deer still have to contend with these enemies but in others, like the UK, humans have killed them off, leaving deer with a relatively peaceful existence. Deer were fully established about 12 million years ago during the Pliocene era. This accounts for their wide global distribution because at that time, the land masses were still connected. Within the deer family, the red deer (Cervus elaphus) is one of the most widely distributed, stretching from New Zealand, through Asia and into Europe. After surviving the Ice Age, red deer migrated to North America and developed a separate life as elk. During summer red deer are dark red or brown but in winter they change to a darker brown or grey. However, their most distinctive feature is not their eponymous colour, but their antlers. In the absence of enemies, the main function of the antlers is in the mating ritual, attracting females and defending them from other males. But now antlers are attracting the attention of scientists because they are the only mammalian tissue capable of repeated regeneration, growing, shedding then regrowing year after year. After the first year of growth, the antlers fall off their supports, the pedicles that protrude from the cranium, and growth of the new antlers begins immediately, a soft velvet outer layer covering the inner bony tissue. The timing of the cycle is closely associated with the seasonal fluctuation of the concentration of androgen hormones in the blood. In spring, androgen levels are low and growth is rapid. When the antlers are fully grown, rising levels of testosterone promote ossification, and the velvet layer is lost. Although it is agreed that hormone levels control antler development, it is arguable whether they affect antler growth directly. It seems likely that cellular signalling molecules are involved, so Korean researchers have undertaken a proteomics study of the growing tips of antlers to try and identify those agents. Senior reporter Byoung Chul Park from the Systemic Proteomics Research Centre of theKorea Institute of Bioscience and Biotechnology in Taejon with colleagues from four other organisations described their methods in Proteomics 2004, 4, 3642. They cut off the bony tissue near the tips and collected blood from the surgical site, then extracted proteins from both for two-dimensional gel electrophoresis. The low-molecular-mass region was poorly resolved, so a second separation was carried out on a different gel, allowing more spots to be isolated. The proteins spots were located by silver staining and extracted for trypsin digestion and analysis by MALDI MS. Current public databases contain a limited number of deer sequences, so other mammalian species were also searched to identify the proteins. More than 800 protein spots were observed in a pattern unique to antler tissue, different even from that of the proximal bony tissue close to the antler pedicle. Moreover, more than 67% of these did not match plasma proteins, confirming that antlers were composed of tissue with different developmental origins. Several major plasma proteins such as immunoglobulin and gamma-globulin were absent from the antler proteome. A total of 130 proteins were identified from the growing tips, and classified into functional types. The presence of growth factors could not be confirmed but several proteins involved in growth factor signalling pathways were identified. Additionally, nuclear receptor proteins and other proteins that may be involved in antler growth, such as fatty acid binding proteins, were found in the tips, implicating them in the growth and differentiation of antlers. The proteome map and database will aid further studies of the development and biological properties of antlers and may lead to therapeutic applications, based on the capacity for regrowth. Related Links
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