Abstract
The annual regeneration cycle of deer (Cervidae, Artiodactyla) antlers represents a unique model of epimorphic regeneration and rapid growth in adult mammals. Regenerating antlers are innervated by trigeminal sensory axons growing through the velvet, the modified form of skin that envelopes the antler, at elongation velocities that reach one centimetre per day in the common deer (Cervus elaphus). Several axon growth promoters like NT-3, NGF or IGF-1 have been described in the antler. To increase the knowledge on the axon growth environment, we have combined different gene-expression techniques to identify and characterize the expression of promoting molecules not previously described in the antler velvet. Cross-species microarray analyses of deer samples on human arrays allowed us to build up a list of 90 extracellular or membrane molecules involved in axon growth that were potentially being expressed in the antler. Fifteen of these genes were analysed using PCR and sequencing techniques to confirm their expression in the velvet and to compare it with the expression in other antler and skin samples. Expression of 8 axon growth promoters was confirmed in the velvet, 5 of them not previously described in the antler. In conclusion, our work shows that antler velvet provides growing axons with a variety of promoters of axon growth, sharing many of them with deer's normal and pedicle skin.
Highlights
The capability to regenerate large sections of the body plan is typical of some invertebrates and urodele amphibians, while in mammals it is almost restricted to organs like the skin or the exceptional deer antlers [1,2]
Whole antler extracts promote neurite outgrowth in vitro [14] and we have shown that velvet -but not mesenchyme- secretes nerve growth factor (NGF) and other molecules that strongly promote neurite outgrowth in vitro [9]
Since previous studies have proposed that the sequence divergence and protein structure similarity among mammals will guarantee valid results [25], we used the well known and highly annotated Affymetrix human U133plus 2 Genechip to carry out the gene expression profiling
Summary
The capability to regenerate large sections of the body plan is typical of some invertebrates and urodele amphibians, while in mammals it is almost restricted to organs like the skin or the exceptional deer antlers [1,2]. Male deers shed (cast) their antlers and fulfill a complete regeneration process that leads to the formation of a new set of antlers in approximately three months. The growing antler is an extension of the antler pedicle periostium [3] that proliferates and differentiates into cartilage and bone tissue to form the bone core of the new antlers. At the end of the summer, antlers become calcified and velvet sheds, leaving the bony core used in agonistic encounters during the rut season
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