Ossification of the mouse metatarsal: Differentiation and proliferation in the presence/absence of a defined growth plate

Abstract

There is significant diversity in growth plate behavior among sites within an individual skeleton and between skeletons of different species. This variation within wild-type animals is an underutilized resource for studying skeletal development. One bone that potentially exhibits the most diverse behavior is the metatarsal. While one end forms a growth plate with an epiphyseal secondary center of ossification as in other long bones, the opposite end undergoes direct ossification in a manner more similar to short bones. Although descriptions of human metatarsal/metacarpal ossification are available, a detailed comparative analysis has yet to be conducted in an animal model amenable to biomolecular analysis. Here we report an analysis of proximal and distal ossification in an age series of mouse metatarsals. Safranin O staining was used for qualitative and quantitative histology, and chondrocyte differentiation and proliferation were analyzed using immunohistochemistry for type X collagen and proliferative cell nuclear antigen expression. We establish that, as in the human, both growth plate formation and direct ossification occur in the mouse metatarsal, with chondrocyte populations showing distinct differentiation patterns at opposite ends of the bone. In addition, growth plate formation is characterized by a peak of proliferation in reserve zone chondrocytes that distinguishes it from both established growth plates and direct ossification. Our analysis demonstrates that the mouse metatarsal is a productive model for investigating natural variation in ossification that can further understanding of vertebrate skeletal development and evolution.

Temperature regulates limb length in homeotherms by directly modulating cartilage growth

“…In all cases, there were more BrdU-positive cells in the epiphyseal region of the MTs when compared with the columnar region of the growth plate (Fig. 4 C and D), as is expected because much early proliferation in vivo occurs in the rounded epiphyseal chondrocytes before the establishment of a mature growth plate (24,25). Our experiments did not extend beyond four days in culture, and so it is possible that a differential temperature effect on the cell populations might occur later in growth.…”

“…The middle 3 metatarsal bones (MT2-4) were harvested from left and right hindpaws of neonatal C57BL/6J mice (housed at room temperature) on the day of birth after decapitation under deep halothane-induced anesthesia as detailed elsewhere (24). Each side was cultured separately at 32°C, 37°C, or 39°C in DMEM growth medium (10% FBS, L-glutamine, fungizone, and gentamycin; Sigma) in humidified incubators with 5% CO 2.…”

“…After a 12-hour labeling period, bones were removed from culture to assess their longitudinal growth (expressed as a percentage change from baseline averaged among MT2-4), fixed and decalcified in Cal-Ex II (Fisher), and processed for routine histology. Serial sections were stained with either Safranin-O for morphological evaluation (25) or BrdU by using a commercially available kit (BD Biosciences). Cells stained positively for BrdU were manually counted in 150-m ϫ 100-m sample regions from the growth plate columnar zone and distal epiphysis of MT3 by using an Olympus BH-2 microscope interfaced to Bioquant Osteo-II image analysis software (BQIAC) (Fig.…”

Proliferating Cells in Knee Epiphyses of Lizards Allow for Somatic Growth and Regeneration after Damage

“…The typical epiphyses shape at the two sides of the femur and tibia likely derives from the increase in the number of proliferating cells in these areas in comparison to the diaphysis, where chondrocytes instead differentiate. Similar observations are also reported for mammalian long bones [28][29][30]. The formation of the metaphysis or growth plate begins at stage 34 when chondroblasts in this region pile up and assume a flat shape.…”

Bone development in the femoral epiphysis of mice: The role of cartilage canals and the fate of resting chondrocytes

“…However, it should be also noted that cartilage canals are not necessarily a prerequisite for endochondral ossification in the long bone extremities. During early development, they appear to be absent in the femoral head of several marsupials and rats, as well as in metatarsals of mice (Thorp, 1990;Morini et al, 1999;Reno et al, 2006).…”