How Deer Grow Antlers

Members of the deer family grow full sets of antlers
every year. Learn what stem cells have to do with this.

Members of the deer family, from moose to caribou to mule deer, vary widely in their antlers. Some forms are simple; others are branching and complex. Some are grown only by males; those of reindeer are grown by both sexes. However they grow, they are among the most distinctive parts of the animal.

Note: Deer (Cervidae) differ from permanently-horned Antelope (Bovidae) but are classified in the same order Artiodactyla, or even-toed ungulates.

Antlers grow very fast in the spring. To figure out how they grow, a team of six researchers in China studied the stem cells responsible for growth of antlers in Tarim red deer native to China. These antlers can grow as much as 2.5 cm per day.

Reindeer are the only deer where both sexes grow antlers. Credit: Duluth Trading, Inc. catalog

HGF/c-Met signaling promotes the migration and proliferation of deer antler MSCs (Wang et al., Nature Scientific Reports, 10 July 2023). As with anything else in biology, antler growth is a complex process involving multiple genes, proteins, cells and signals.

The complete regeneration of deer antlers is based on the proliferation and differentiation of stem cells. Mesenchymal stem cells (MSCs) of antlers have an important role in antler regeneration and rapid growth and development. HGF [hepatocyte growth factor] is mainly synthesized and secreted by mesenchymal cells. After binding to its receptor c-Met, which transduces signals into cells to stimulate cell proliferation and migration in various organs to promote tissue morphogenesis and angiogenesis. However, the role and mechanism of the HGF/c-Met signaling pathway on antler MSCs are still unclear.

This signaling pathway, they found, is a trigger for many other processes. Each of the other pathways signals others, and so on.

Caribou: headgear is often a major contributor to an animal’s appearance.

The process of antler growth involves signals within the stem cells, and migration of those cells into the right places. More pathways are involved in the migration step.

In this study, we established antler MSCs with overexpression and interference of HGF gene by lentivirus and small interference RNA, observed the effect of HGF/c-Met signal pathway on the proliferation and migration of antler MSCs, and detected the expression of downstream related signal pathway genes, to explore the mechanism of HGF/c-MET signal pathway on the proliferation and migration of antler MSCs. The results showed that the HGF/c-Met signal affects the expression of RAS, ERK and MEK genes, regulates the proliferation of pilose antler MSCs through Ras/Raf, MEK/ERK pathway, affects the expression of Gab1, Grb2, AKT and PI3K genes, and regulates the migration of MSCs of pilose antler through Gab1/Grb2 and PI3K/AKT pathway.

What this means, briefly, is that one pathway regulates multiple other pathways. A pathway involves expression of genes, signals to cells, and movement of parts to complete a process.

The mesenchymal stem cells (MSCs) responsible for antler growth—recently discovered—are unique in their high growth rates. This makes them interesting for possible human health applications.

A study found that the proliferation ability of Antler stem cells (AnSCs) is significantly stronger than that of human placenta mesenchymal stem cells in vitro. Furthermore, an animal experiment reported a higher skin wound healing in rats treated with antler MSCs than of human umbilical cord mesenchymal stem cells and rat bone marrow mesenchymal stem cells, further indicating that AnSCs are a class of stem cells with great clinical applications.

Such rapid growth would seem a risk for cancer. Antler growth, however, succeeds in preventing tumor initiation and growth.

Previous studies have shown that both tumor suppressor genes and proto-oncogenes in deer are positively selected so that antler MSCs with a significantly higher proliferation rate of cancer cells do not become cancerous during the rapid growth period…. HGF/c-Met regulates biological events such as proliferation, migration and morphogenesis of normal cells, but HGF and c-Met are abnormally expressed in many cancers. The binding of HGF to its receptor c-Met can induce dimerization of c-Met and autophosphorylation of tyrosine residues in the carboxy-terminal domain of c-Met, resulting in downstream MAPK, PI3K, RAS and ERK. Also, other signal transduction molecules are sequentially activated, thereby promoting the conduction of downstream signals and participating in the regulation of cell survival, proliferation, and invasion.

As many as seven genes and their pathways are regulated by the HGF/c-Met pathway. Without mentioning evolution, the authors say in conclusion that their research only constitutes a beginning to understanding the complex process of antler growth.

The migration and proliferation ability of antler MSCs are crucial for antler tissue regeneration. We suggest that HGF/c-Met signaling has an important regulatory role in the migration and proliferation ability of antler MSCs, and the results of this study provide an important theoretical supplement to explore the mechanism of rapid antler growth and regeneration.

Headgear on ruminants is highly varied. Spotted deer (Cervidae) with oryx (Bovidae). Corel Photos.

Many further questions can stem from this team’s findings. For instance, if cells are local to the stump of a growing antler, how do the two antlers maintain their bilateral symmetry, such that they branch at almost exactly the same points while separated by many centimeters to feet apart? Don’t ask they deer. They don’t know.

Anybody want to explain this by the “evolution pathway” of random mutations and ‘stuff happens’? Ha.