Growth and shaping of metacarpal and carpal cartilage anlagen: application of morphometry to the development of short and long bone. A study of human hand anlagen in the fetal period

Fin systems comparative anatomy in model Batoidea Raja asterias and Torpedo marmorata: Insights and relatioships between musculo-skeletal layout, locomotion and morphology

The macroscopic and microscopic morphology of the appendicular skeleton was studied in the two species Raja asterias (order Rajiformes) and Torpedo marmorata (Order Torpediniformes), comparing the organization and structural layout of pectoral, pelvic, and tail fin systems. The shape, surface area and portance of the T. marmorata pectoral fin system (hydrodynamic lift) were conditioned by the presence of the two electric organs in the disk central part, which reduced the pectoral fin surface area, suggesting a lower efficiency of the "flapping effectors" than those of R. asterias. Otherwise, radials' rays alignment, morphology and calcification pattern showed in both species the same structural layout characterized in the fin medial zone by stiffly paired columns of calcified tiles in the perpendicular plane to the flat batoid body, then revolving and in the horizontal plane to continue as separate mono-columnar rays in the fin lateral zone with a morphology suggesting fin stiffness variance between medial/lateral zone. Pelvic fins morphology was alike in the two species, however with different calcified tiles patterns of the 1st compound radial and pterygia in respect to the fin-rays articulating perpendicularly to the latter, whose tile rows lay-out was also different from that of the pectoral fins radials. The T. marmorata tail-caudal fin showed a muscular and connective scaffold capable of a significant oscillatory forward thrust. On the contrary, the R. asterias dorsal tail fins were stiffened by a scaffold of radials-like calcified segments. Histomorphology, heat-deproteination technique and morphometry provided new data on the wing-fins structural layout which can be correlated to the mechanics of the Batoid swimming behavior and suggested a cartilage-calcification process combining interstitial cartilage growth (as that of all vertebrates anlagen) and a mineral deposition with accretion of individual centers (the tiles). The resulting layout showed scattered zones of un-mineralized matrix within the calcified mass and a less compact texture of the matrix calcified fibers suggesting a possible way of fluid diffusion throughout the mineralized tissue. These observations could explain the survival of the embedded chondrocytes in absence of a canalicular system as that of the cortical bone.

The combined cartilage growth - calcification patterns in the wing-fins of Rajidae (Chondrichthyes): A divergent model from endochondral ossification of tetrapods

The relationship between cartilage growth - mineralization patterns were studied in adult Rajidae with X-ray morphology/morphometry, undecalcified resin-embedded, heat-deproteinated histology and scanning electron microscopy. Morphometry of the wing-fins, nine central rays of the youngest and oldest specimens documented a significant decrement of radials mean length between inner, middle and outer zones, but without a regular progression along the ray. This suggests that single radial length growth is regulated in such a way to align inter-radial joints parallel to the wing metapterygia curvature. Trans-illumination and heat-deproteination techniques showed polygonal and cylindrical morphotypes of tesserae, whose aligned pattern ranged from mono-columnar, bi-columnar, and multi-columnar up to the crustal-like layout. Histology of tessellated cartilage allowed to identify of zones of the incoming mineral deposition characterized by enhanced duplication rate of chondrocytes with the formation of isogenic groups, whose morphology and topography suggested a relationship with the impending formation of the radials calcified column. The morphotype and layout of radial tesserae were related to mechanical demands (stiffening) and the size/mass of the radial cartilage body. The cartilage calcification pattern of the batoids model shares several morphological features with tetrapods' endochondral ossification, that is, (chondrocytes' high duplication rate, alignment in rows, increased volume of chondrocyte lacunae), but without the typical geometry of the metaphyseal growth plates. RESEARCH HIGHLIGHTS: 1. The wing-fins system consists of stiff radials, mobile inter-radial joints and a flat inter-radial membrane adapted to the mechanical demand of wing wave movement. 2. Growth occurs by forming a mixed calcified-uncalcified cartilage texture, developing intrinsic tensional stresses documented by morphoanatomical data.

Morphology of joints and patterns of cartilage calcification in the endoskeleton of the batoid Raja cf. polystigma

The skeleton of the batoid fish consists of a mixture of calcified and uncalcified cartilage with a typical layout of mineral deposition toward the outer border, leaving an uncalcified central core in most of the skeleton segments. An exception is observed in the radials, where mineral deposition is central. Joints and endoskeleton segments were studied in two adult samples of Raja cf. polystigma. Histomorphology, mineral deposition pattern, and zonal chondrocyte duplication activity were compared among several endoskeleton segments, but with particular attention to the fin rays; in the first, the uncalcified cartilage is central with an outer layer ranging from mineralized tesserae to a continuous calcified coating, whereas in the second, the uncalcified cartilage surrounds one or more central calcified columns. The diarthroses have a joint cavity closed by a fibrous capsule and the sliding surfaces rest on the base of mineralized tesserae, whereas the interradial amphiarthroses show a layer of densely packed chondrocytes between the flat, calcified discs forming the base of neighboring radials. In the endoskeleton segments, three types of tesserae are distinguished, characterizing the phases of skeletal growth and mineralization which present differences in each endoskeleton segment. The chondrocyte density between central core, subtesseral layer, and radial external cartilage did not show significant differences, while there was a significant difference in chondrocyte density between the latter zones and the type c tesserae of the pelvic girdle. The histomorphology and morphometry observed in Raja cf. polystigma suggest a model of cartilage growth associated with structural stiffening without remodeling. A key point of this model is suggested to be the incomplete mineralization of the tesseral layer and the continuous growth of cartilage, both enabling fluid diffusion through the matrix fibril network of scattered, uncalcified cartilage zones inside and between the tesserae.

Long bone human anlage longitudinal and circumferential growth in the fetal period and comparison with the growth plate cartilage of the postnatal age

The patterns of longitudinal and peripheral growth were analyzed in human autopod cartilage anlagen (fetal developmental stage 20th-22nd week) through morphometric assessment of chondrocyte parameter size, shape, alignment and orientation between peripheral and central sectors of the anlage transition zone defined by primary ossification center and the epiphyseal basis. The aim was to correlate the chondrocyte dynamics with the longitudinal and peripheral growth. A further comparison was carried out between the corresponding sectors of the postnatal (3-5 months old) growth plate cartilage documenting: (1) the different chondrocyte framework and the new peripheral mechanism; (2) the opposite direction of fetal periosteal ossification versus the Lacroix bone bark. Measurement of multiple parameters (% lac area, % total matrix area, total lac density and mean single lac area), which characterize the cartilage Anlage growth, suggested the following correlations with chondrocyte duplication rate: (a) slow duplication rate ≈ coupled, intralacunar chondrocytes (in central epiphysis); (b) repeated/frequent cell duplications ≈ clusters (in the basal epiphyseal layer); (c) clusters of chondrocytes before becoming hypertrophic were stacked up on the top of each other (both in the Anlage transition zone or in the columns of metaphyseal growth plate); (d) enhanced osteoclastic resorption of the Lacroix bone bark lower end, extended to the more external metaphyseal trabeculae counterbalancing the discrepancy between the epiphyseal and the diaphyseal circumferential growth.

The missing segment of the autopod 1st ray: new insights from a morphometric study of the human hand

Whether the 1st segment of the human autopod 1st ray is a 'true' metapodial with loss of the proximal or mid phalanx or the original basal phalanx with loss of the metacarpal has been a long-lasting discussion. The actual knowledge of the developmental pattern of upper autopod segments at a fetal age of 20-22 weeks, combined with X-ray morphometry of normal long bones of the hand in the growing ages, was used for analysis of the parameters, percentage length, position of epiphyseal ossification centers and proximal/distal growth rate. The symmetric growth pattern in the fetal anlagen changed to unidirectional in the postnatal development in relation to epiphyseal ossification formation. The percentage length assessment, the distribution of the epiphyseal ossification centers, and differential proximal/distal growth rate among the growing hand segments supported homology of most proximal segment of the thumb with the 2nd-5th proximal phalanges and that of the proximal phalanx of the thumb with the 2nd-5th mid phalanges in the same hand. Published case reports of either metanalysis of 'triphalangeal thumb' and 'proximal/distal epiphyseal ossification centers' were used to support the applied morphometric methodology; in particular, the latter did not give evidence of growth pattern inversion of the proximal segment of the thumb. The presented data support the hypothesis that during evolution, the lost segment of the autopod 1st ray is the metacarpal.