The Anatomical Foundation for Multidisciplinary Studies of Animal Limb Function: Examples from Dinosaur and Elephant Limb Imaging Studies

Abstract

The identity of the cells that form the periosteum during development is controversial with current dogma suggesting these are derived from a Sox9-positive progenitor. Herein, we characterize a newly created Prrx1eGFP reporter transgenic mouse line during limb formation and postnatally. Interestingly, in the embryo Prrx1eGFP-labeled cells become restricted around the Sox9-positive cartilage anlage without themselves becoming Sox9-positive. In the adult, the Prrx1eGFP transgene live labels a subpopulation of cells within the periosteum that are enriched at specific sites, and this population is diminished in aged mice. The green fluorescent protein (GFP)-labeled subpopulation can be isolated using fluorescence-activated cell sorting (FACS) and represents approximately 8% of all isolated periosteal cells. The GFP-labeled subpopulation is significantly more osteogenic than unlabeled, GFP-negative periosteal cells. In addition, the osteogenic and chondrogenic capacity of periosteal cells in vitro can be extended with the addition of fibroblast growth factor (FGF) to the expansion media. We provide evidence to suggest that osteoblasts contributing to cortical bone formation in the embryo originate from Prrx1eGFP-positive cells within the perichondrium, which possibly piggyback on invading vascular cells and secrete new bone matrix. In summary, the Prrx1eGFP mouse is a powerful tool to visualize and isolate periosteal cells and to quantify their properties in the embryo and adult.

Skeletal pathology and variable anatomy in elephant feet assessed using computed tomography

“…Best-known amongst these is variable phalangeal number, especially in DI and DV (Ramsay & Henry, 2001; Fowler, 2006; Hutchinson et al, 2008; Siegal-Willott, Alexander & Isaza, 2012). Our data also support this longstanding observation of elephants, and confirm that digits II, III and IV generally have three phalanges (although exceptions existed, especially amongst Asian elephants).…”

“…The degree of ossification of “predigits” (prepollex/prehallux, or radial/tibial sesamoids; e.g., Hutchinson et al, 2008; Hutchinson et al, 2011) was also noted, and categorised as: non-ossified (code 0), minimally ossified (code 1), moderate ossification embedded in (presumably) cartilaginous soft tissue (code 2), or extensively ossified single structure (code 3). Anatomical variability in the proximal sesamoid bones was described.…”

Response: Of ideas, dichotomies, methods, and data – how much do elephant kinematics differ from those of other large animals?

“…Indeed our unpublished in vitro and radiographic data support the assumption that the toes move very little and that our markers were positioned on skeletal landmarks that enable approximation of ankle joint motion. Paul repeats descriptions of the same foot (and footpad) anatomy and function that we have described in three papers on that subject (Weissengruber et al, 2006;Hutchinson et al, 2008;, so we do not see what he is critiquing. Again, he is providing no new information.…”

Some basic relationships between density values in cancellous and cortical bone

“…The specimen was the right femur of an adult Asian elephant (3432 kg; 24 years old) and was representative of other elephant femora we have examined recently (Hutchinson et al, 2008). The specimen was collected shortly after the animal's euthanasia (for reasons unrelated to this study) at Whipsnade Zoo (Bedfordshire, UK) and frozen (À20 1C) until sample testing.…”