Embryonic Joint Research Articles

Collagen gene expression during development of avian synovial joints: Transient expression of types II and XI collagen genes in the joint capsule

The developmental sequence of the embryonic joint has been well studied morphologically. There are, however, no definitive studies of cell function during joint development. In order to begin to understand the differentiation events that contribute to joint formation, we examined the expression of collagen mRNAs encoding types I, IIA, IIB, and XI. In situ hybridization was performed on chicken embryo hind limb buds and digits from day 7 to day 18 (Hamburger and Hamilton stages 31-44). In the day 7 (stage 31) limb bud, there was a condensation of mesenchyme forming the primitive tarsal and metatarsal bones that showed abundant expression of type IIA procollagen message, but no type IIB or type alpha 1(XI) message. By day 8 (stage 33), co-expression of types IIA, and type XI procollagen mRNAs was observed in the condensations, with expression of IIB restricted to early chondrocytes with metachromatically staining matrix. At this stage, DNA fragmentation characteristic of apoptosis was observed in cells near the midline of the interzone region between the developing anlagen, and in areas between and around the individual digits of the paddle. The presumptive apoptotic cells were more numerous at day 9 (stage 35), and were not found in the developing joint at subsequent time points, including the initiation of spatial cavitation of the joint. From days 11-18, type IIA procollagen mRNA was expressed in flattened cells at the surface of the anlagen, and in the perichondrium and in the developing joint capsule; type IIB mRNA message was found only in chondrocytes. Type XI mRNA was expressed by all type II-expressing cells. Alpha 1(I) mRNA was expressed early by cells of the interzone and capsule, but as cavitation progressed, the type I expressing cells of the interzone merged with the superficial layer of the articular surface. Thus, at the time of joint cavitation, there was a distinct pattern of expression of procollagen messages at the articular surface, with type I being outermost, followed by morphologically similar cells expressing type IIA, then chondrocytes expressing type IIB. The progenitor cells expressing type IIA message define a new population of cells. These cell populations contribute to the molecular heterogeneity of the articular cartilage, and these same populations likely exist in the developing joints of other species. The transient transcription of type II and type XI collagen genes, characteristic of chondrocytes, by cells in the joint capsule demonstrates that these cells may have chondrogenic potential.

Development of the metatarsophalangeal joint of the chick embryo: morphological, ultrastructural and histochemical studies.

The histogenesis and mechanism of joint clefting of the developing chick embryo up to the fifteenth day of incubation have been studied morphologically, ultrastructurally, and by histochemical methods. Cell degeneration was consistently noted 24 hours after differentiation of the joint tissue, and it is postulated that this early cell necrosis might account for the loosening of the medial part of articular mesenchyme (interzone) leading to differentiation of a three-layered embryonic joint. At the time of joint clefting degenerative cells were also seen in the peripheral parts of the developing articular cavity. In some cases clefting was immediately preceded and/or accompanied by the appearance of elongated, basophilic and electron-opaque cells closely arranged along the zone of tissue cleavage. These cells were thought to be implicated in some way in the clefting process and later to constitute a surface cell layer of articular cartilage. In addition to these observations clear morphological and histoautoradiographic evidence was found for the presence of an organic component, presumably mucopolysaccharide, in the primitive synovial fluid. Fluid secretion might also account for tissue cleavage at the sites of its accumulation. The data reported here suggest that joint cavity formation results from a combination of both intrinsic, genetically expressed and extrinsic mechanical factors acting synchronously.

The role of movement in embryonic joint development

The role of movement in embryonic joint development

Early Transverse Dykes in the Main Donegal Granite

AbstractCertain microtonalite dykes cut across the flow banding of the Main Donegal Granite in the direction of an important cross-joint, yet they and their granite host are shown to have crystallized together and in the same manner as both the darker flow bands in the granite and the pelitic xenoliths within it. It appears that an embryonic joint system existed in the Donegal Granite before consolidation and crystallization were complete. It is suggested that the early dykes represent metasomatized pelitic enclave material and are not differentation products of granitic magma. Comparison is made with the basic analogue provided by the beerbachite enclaves and dykes of the hypersthene-gabbro of Ardnamurchan.