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R Amprino

Publications and source records attributed to R Amprino.

At least 19 recordsLinked to original sources
PubMed1985

The influence of stress and strain in the early development of shaft bones. An experimental study on the chick embryo tibia.

In chick embryos from stage 23 to stage 27 the whole presumptive zeugopod - or its pre-axial (tibial) portion only - was proximodistally and dorsoventrally inverted by turning it 180 degrees round the anteroposterior axis of the limb bud. Development of the reoriented blastema of the tibia was consistently retarded and variously reduced: this skeletal piece appeared shorter and relatively thicker than the controlateral normal tibia. Chondrification, progress of differentiation of the cartilaginous model, onset and gradual spreading of the ossification processes were considerably delayed. Often the diminutive tibia underwent a degree of bending or angulation of up to 90 degrees - 100 degrees in the sagittal plane. In these bent tibiae - obviously developing under abnormal conditions of intrinsic and extrinsic mechanical stresses - cell hypertrophy appeared greatly retarded or hindered in sites of the diaphysial cartilaginous core which were presumably subjected to strong longitudinal compression. No rigorous temporal and topographical relationships were observed between chondrocyte hypertrophy and onset of perichondral osteogenesis. Apparently, a direct contact between hypertrophic cartilage and perichondrial cells was not strictly required to prompt osteogenesis; this process, in fact, often involved areas of the perichondrium enveloping parvicellular cartilage. Radial pressures exerted by the over-stretched outer layer of the perichondrium, or periosteum, on the subjacent prospective osteogenous layer reduced or prevented the deposition of bone. Conversely, radial stretching of the inner layer of the perichondrium, or periosteum, considerably enhanced cell proliferation, blood vessel formation, differentiation of osteoblasts and formation of bone matrix.

Animals↗
PubMed1984

The development of the vertebrate limb.

Knowledge of the early development of the tetrapod limb largely rests on studies conducted on the chick embryo, the main object of descriptive and experimental work on limb morphogenesis for the last 40 years. A short account is given here of the origin and gradual changes in size and shape of the limb bud, the structure of its ectodermal and mesodermal components, and the mechanisms at play during the early phases of the organogenesis of the skeletal pieces, joints, and muscles. From studies on the causality of limb morphogenesis in both amphibian and avian embryos, it appears that the mesodermal component of the primitive limb area, activated by influences exerted by the adjacent somitic mesoderm, is the primary seat of the limb developmental potencies. The limb type, the establishment of the limb axes, and the individuation, determination, and differentiation of the limb articles in a definite temporal sequence according to an orderly proximodistal pattern seem to be inherent properties of the mesoderm. Uncertainties exist as to (1) the nature of interactions between mesoderm and ectoderm in limb-bud outgrowth and pattern formation and (2) the precise role(s) played by the ectoderm, particularly by its apical thickening--a structure that, after all, does not form in urodeles and some anurans. Mention is also made of the regulation ability of chick limb-bud and of recent attempts to stimulate limb regeneration in mammals.

Amphibians↗
PubMed1983

[Morphogenetic factors and mechanisms in the articulation of limbs].

After excision or reorientation of a part of the tibia rudiment in the chick embryo, an articular head or a heterotopic joint may develop by regulation without direct or indirect participation of the interzonal mesenchyme. The undifferentiated cells which take part in the regulation arise from the prospective perichondrium: their proliferation, organization and incorporation are controlled by influences exerted by the adjacent parts of the skeletogenous blastema. Other experiments have been performed on the tibia rudiment in the attempt to modify the pressures exerted along the zeugopod by its growing skeleton. When the pressures are reduced, a joint can form between the distal end of the tibia and the proximal tarsal, which undergo fusion in normal development. As an effect of increased longitudinal pressures, fusion of the proximal tarsal and the proximal epiphysis of the 180 degrees inverted tibia may occur in spite of the interposition of a part of the interzonal mesenchyme of the knee. Our results stress the primary role seemingly exerted by the growing articular ends of the skeletal pieces during joint formation; under the conditions of our experiments, joint development does not seem causally related to any special morphogenetic property of the interzonal mesenchyme. In some joints, menisci, ligaments, fatty pads differentiate from parts of the interzonal mesenchyme which are apparently endowed with a special and early determination; it is still unknown, however, whether the interzonal mesenchyme also plays a more general role in all the joints.

Animals↗
PubMed1981

[Experimental changes in the sites of presumptive articular areas].

Following proximo-distal and dorso-ventral reorientation of about the proximal (or distal) half of the chick embryo tibial rudiment, changes of the original morphogenetic fate of the latter occur. In the embryos operated upon between stage 24 and stage 26, from the bisected blastema two diminutive, tandem skeletal pieces each built of a diaphysis and two articular ends can develop. More restricted organogenetic changes take place when the tibial rudiment is divided during early phases of its chondrification (stage 26-27 1/2); in these cases, the presumptive diaphyseal (or metaphyseal) zone lying at one of the ends of both segments of the bisected tibia gives rise to an epiphysis sometimes reduced but often exhibiting an articular surface. The early rudiment of a long bone can, therefore, be viewed as an unitary morphogenetic field endowed with a remarkable plasticity. The site of the joints seems not to be definitely determined until the articular ends of the skeletal pieces undergo chondrification.

Animals↗
PubMed1979

Developmental interactions between the adjacent parts of combined heterologous skeletogenous territories.

The right limb buds of chick embryos (H.-H.stages 22 to 26) were transversely divided at approximately the presumptive zeugopod mid-length, and (1) the distal parts exchanged between wing and hind-limb bud in apdv-reversed orientation (operation A), or (2) the severed distal part of the leg bud was reoriented in situ (operation B). Both the proximal and distal segments of the zeugopodal bones developing from the recombined portions of presumptive heterologous territories showed characteristic differences of size and shape in comparison to the corresponding parts of the skeletal pieces of the zeugopod of the intact, control limbs. These developmental changes are interpreted as being the consequence of reciprocal influences exerted by the adjacent parts of mesenchymal territories (or blastemata) that, under normal developmental conditions, are destined to give rise to different bones. Such influences may enhance or depress the growth potential of the skeletogenous populations affected, and, within each cell population, modify the geometry of the growth processes by which the various parts of each skeletal piece attain their typical shape.

Animals↗
PubMed1979

[Experimental data on the development of the primordia of the long bones of chick embryo extremities].

By means of various kinds of recombination of the two halves of the chick limb buds transected at the presumptive zeugopod mid-length a continuity was established between the opposite portions of the mesenchymal precursors of heterologous shaft bones of the zeugopod. In later development, both proximal and distal components of the recombined skeletal pieces consistently showed variously marked differences in size and shape in comparison with the corresponding parts of the control bones. Reciprocally, from the opposite portions of the presumptive territory of each zeugopodal bone separated the one from the other so that they could not contact and fuse, hypoplasic pieces developed which failed to attain the size and shape typical of the control segments. Those observations seem to show that morphogenetic interactions reciprocally exerted between the various parts of the presumptive territory of each shaft bone are mandatory to ensure the normal development of these skeletal pieces.

Animals↗
PubMed1977

Further observations on the site of bone prospective areas in the chick embryo wing bud.

The portion of the pre-axial region of the wing bud anterior to the cranial boundary of the skeletogenous territory of the stylo-zeugopod, according to Stark and Searls' recent maps, was surgically isolated in chicken embryos of the stages 18-25, and autoplastically grafted to the dorsal surface of the hind-limb bud or to the trunk. In other embryos of the same stages the cranial half or the cranial two thirds of the pre-axial region mentioned were isolated and heterotopically implanted. The experimental results consistently showed that the isolate contained a variously large portion of the presumptive radius and a significant part of the proximal half of the prospective humerus. In fact, the skeletal parts mentioned did not develop in situ in the donor wing while they differentiated, in general, in the implantation site. In this regard, the present research confirms data from previous experiments showing that Stark and Searls' maps do not offer an accurate representation of the position and the cranio-caudal width of the presumptive areas of the skeletal pieces of the wing. Our findings seem also to indicate that the major (or longitudinal) axis of the future radius is arranged along the proximodistal axis of the wing bud throughout the developmental stages mentioned; instead, the major axis of the future humerus undergoes a gradual shift, being first (stages 18-20) arranged nearly parallel to the bud base and getting more and more parallel to the proximo-distal axis of the wing bud through stages 21-24. Besides, between stage 18 and 25 the cranio-caudal width of the presumptive skeletogenous territory of the zeugopod, and to a lesser extent of the stylopod, seems to undergo a slight relative reduction with respect to the cranio-caudal thickness of the whole wing bud; this might depend on a process of aggregation of the prospective skeletogenous cells into gradually denser and more defined precartilaginous blastemes.

Animals↗