Table 1.
Overview of the comparisons between hair follicles and deer antlers.
| Similarities | ||
|---|---|---|
| Nature | Hair follicle | Antler unit |
| Mammalian organ | Mammalian organ | |
| Structure of mature organ | Permanent (infundibulum and isthmus) + cyclic (suprabulbar strand and bulb) components | Permanent (pedicle) + cyclic (antler) components |
| Ontogeny | Organogenesis and cyclic regeneration | Organogenesis and cyclic regeneration |
| Order of organogenesis | Permanent component formed first and cyclic component formed second | Permanent component formed first and cyclic component formed second |
| Nature of ontogeny | Stem-cell-based (bulge cells) | Stem-cell-based (AP and PP cells) |
| Location of stem cells | In permanent component | In permanent component |
| Initial identification of stem cells | Through tissue graft and genetic marker (LacZ gene) labeling, but not tissue deletion | Through tissue graft and genetic marker (LacZ gene) labeling, but not tissue deletion |
| Attributes of stem cells | Express embryonic stem-cell markers: Oct4, Nanog, and SOX2. Can differentiate into multiple cell lineages | Express embryonic stem-cell markers: Oct4, Nanog, and SOX2. Can differentiate into multiple cell lineages |
| Location of growth centre | In the cyclic component | In the cyclic component |
| Activation of generation and regeneration | By interactions between stem cells and the niche cell types (bulb cells) | By interactions between stem cells and the niche cell types (skin cells) |
| Process of appendage shedding | Enzymes are involved in a proteolytic process | Enzymes are involved in a proteolytic process |
| Endocrine control factors | Main factor: androgen | Main factor: androgen |
| Paracrine control factors | Main factor: IGF1 | Main factor: IGF1 |
| Molecules possibly involved in the interactions between stem cells and niche cells | Including canonical Wnt/β-catenin signaling, sonic hedgehog, and VEGF | Including canonical Wnt/β-catenin signaling, sonic hedgehog, and VEGF |
| Molecules possibly involved in maintenance of stem-cell stemness | Including c-myc | Including c-myc |
|
| ||
| Differences | ||
| Nature of organ | Epithelium | Mesenchyme |
|
| ||
| Organ encapsulation | A layer of mesenchymal tissue | A layer of epithelial tissue |
| Order of structural components | Distal, permanent, proximal, cyclic | Distal, cyclic, proximal, permanent |