The moose mouse, or Moomouse, lives in wooded areas and are found in Northeastern America and through out Canada. They are essentially a species of rodent that has evolved the morphological novelty of antlers, which are typically not seen on smaller mammals, thus makes the moomouse unique in its phylogeny. They have lengthened claws to grab onto trees or use for protection purposes if their antlers are growing at that moment. They have normal fur growth but a reduced sensitivity to cold. The moomice are about the size of regular mice, with the males having miniature antlers so they can defend their territories, fight predators, and attract mates. All moomice have modified claws as a means for climbing up trees and using them as weapons if necessary. They also have fur growth and reduced sensitivity to cold so they could survive the winters. All these traits combined form the moomouse.
The moomouse antlers are only part of the males, so they could fight for territory, fight off predators, and attract mates. The larger and more symmetrical the antlers were the more attractive they are to mates, and the less chance that they will be challenged for their territory.
The process of antler development of the moomouse is like that of a red deer and involves insulin-like growth factor I (IGF-I) which is an important systemic regulator of the pedicle formation as it stimulates proliferation of osteogenic cells from all four ossification stages. Growth factors include epidermal growth factor (EGF) which stimulates cell growth, proliferation and differentiation by binding to the EGF receptor (Price et al.), fibroblast growth factor 2 (FGF-2) and vascular endothelial growth factor (VEGF), and their receptors FGFR1, FGFR2 and FGFR3, and VEGFR-2 respectively. Both signaling systems are widely expressed in the integument and osseocartilaginous compartments. FGF-2 was found in the same cells as all three FGFRs, indicating that FGF signaling may be principally autocrine. FGF-2 induces expression of VEGF, to stimulate and maintain high rates of neovascularization and angiogenesis, thereby providing nutrients to both velvet and bone as they rapidly grow and develop. Bone morphogenetic proteins (BMPs) 2, 4 and 14 and the BMP receptors BMPR1B and ACTRII are also present. These growth factors signal between the osseocartilaginous and skin compartments of the primary antler (Price et al.). These different proteins and growth factors work together in the formation of antlers.
The development of lengthened claws come in handy for the moomice when they have to fight for territory, climb up trees, or ward off a predator. The development of a longer claws is achieved through a three-part process. The first part is an epithelial thickening for an epithelial appendage, this placode formation is observed before the formation of hair follicles. Successful placode induction depends upon the inhibition of BMP4 expression by noggin. WNT-7A expression is vital for correct orientation of the placode along the dorso-ventral axis; in mice lacking normal WNT-7A function the footpads form on the dorsal instead of the ventral surface of the digit tips and this causes the claws to shortened. The second part involves formation of the claw fold and specification of cells forming the germinal matrix. Evidence from feather and hair development indicates that sonic hedgehog (SHH) plays an important role in elongation of feathers and hair, so SHH is therefore also likely to be important for development of the claw fold. In the third part of claw development MSX1 and MSX2 expression affects the length of the claw by regulating the proliferation of cells in the germinal epidermal matrix. These MSH-like genes play an important role in cell proliferation since their expression is associated with regions adjacent to the progress zone of developing limb buds. During skin development MSX1 and -2 often show overlapping, but not identical, expression domains in regions where active cell proliferation takes place. MSX1 expression maintains cells in a proliferating, “dedifferentiated,” state. In contrast, MSX2 has the opposite role of limiting cell proliferation and accelerating differentiation. Overexpression of MSX2 in mouse hair follicles leads to an increase in the number of cells passing from a proliferating stage to a differentiating stage, whereas MSX2 deficiency in mice produces a marked lengthening of the claws (Hamrick). So this means by reducing the expression of MSX2 the claws on the moomice are lengthened.
The moomice have brown fur to better blend in with their woodland environments. The brown color of their fur is caused by the binding of alpha melanocyte stimulating hormone (a-MSH) to the MC1R protein, which in turn increases the levels of cyclic AMP which causes tyrosinase to be expressed with the result being eumelanin (NIH). To get the brown pigment the agouti protein needs to inhibit the binding of a-MSH for short periods of time so that some phaeomelanin is expressed as well, and the fur is a mix of mostly eumelanin and some phaeomelanin to appear brown. They also have the TPVR3 gene that reduces their sensitivity to the cold and allows them to survive through the winter (Callaway), which is an advantage as winters in Northeastern America can be brutal.
Tissue Cell. 2007 Feb;39(1):35-46. Epub 2007 Feb 20.
The distribution of the growth factors FGF-2 and VEGF, and their receptors, in growing red deer antler.
Lai AK, Hou WL, Verdon DJ, Nicholson LF, Barling PM.
Journal of Anatomy Volume 207, Issue 5, November 2005, Pages 603–618
Deer antlers: a zoological curiosity or the key to understanding organ regeneration in mammals?
J. S. Price, S. Allen, C. Faucheux, T. Althnaian, J. G. Mount
MC1R gene, Melanocortin 1 Receptor, National Institute of Health: US National Library of Medicine, reviewed March 2007, Published December 21, 2016
Mammoth genomes hold recipe for Arctic elephants, Ewen Callaway, Moodle Site
Development and evolution of the mammalian limb: adaptive diversification of nails, hooves, and claws, Mark W. Hamrick, First published: September 2001