User:Alejandrobc95/sandbox

Be bold, be brave. . But also, don't forget to be happy.

Transcription factors involved in chondrogenesis
The molecule sonic hedgehog (Shh) modifies the activation of the L-Sox5, Sox6, Sox9 and Nkx3.2. Sox9 and Nkx3.2 induce each other in a positive feedback loop where Nkx3.2 inactivates a Sox9 inhibitor. This loop is supported by BMP expression. The expression of Sox9 induces the expression of BMP, which causes chondrocytes to proliferate and differentiate. L-Sox5 and Sox6 share this common role with Sox9. L-Sox5 and Sox6 are thought to induce the activation of the Col2a1 and the Col11a2 genes, and to repress the expression of Cbfa1, a marker for late stage Chondrocytes. L-Sox5 is also thought to be involved primarily in embryonic chondrogenesis, while Sox6 is thought to be involved in post-natal chondrogenesis. The molecule Indian hedgehog (Ihh) is expressed by prehypertrophic chondrocytes. Ihh stimulates chondrocyte proliferation and regulates chondrocyte maturation by maintaining the expression of PTHrP. PTHrP acts a patterning molecule, determining the position in which the chondrocytes initiate differentiation.

Cartilage in invertebrates
Mollusks

Cephalopods: the models used for the studies of cartilage in cephalopods are Octopus vulgaris and Sepia officinalis. The cephalopod cranial cartilage is the invertebrate cartilage that shows more resemblance to the vertebrate hyaline cartilage. The growth is though to take place through out the movement of cells from the periphery to the center. The chondrocytes present different morphologies related to their position in the tissue. . The embryos of Sepia officinalis express ColAa, ColAb and hyaluronan in the cranial cartilages and other regions of chondrogenesis. This implies that the cartilage is fibrillar-collagen-based. The Sepia officinalis embryo expresses hh, whose presence causes ColAa and ColAb expression and is also able to maintain proliferating cells undifeentated. It has been observed that this species presents the expression SoxD and SoxE, analogs of the vertebrate Sox5/6 and Sox9, in the developing cartilage. The cartilage growth pattern is the same than in vertebrate cartilage.

Gastropods: the interest lies on the odontophore, a cartilaginous structure that supports the radula. The most studied species regarding to this particular tissue is Busycon canaliculatum. The odontophore is a vesicular cell rich cartilage, consisting on vacuolated cells containing myoglobin, surrounded by a low amount of extra cellular matrix containing collagen. The odontophore contains muscle cells along with the chondrocytes in the case of Lymnaea and other mollusks that graze vegetation.

Arthropods

The most studie cartilage in arthropods is the Limulus polyphemus branchial cartilage. It is a vesicular cell-rich cartilage due to the large, spherical and vacuolated chondrocytes with no homologies in other arthropods. Other type of cartilage found in Limulus polyphemus is the endosternite cartilage, a fibrous-hyaline cartilage with chondrocytes of typical morphology in a fibrous component, much more fibrous than vertebrate hyaline cartilage, with mucopolysaccharides inmunoreactive against chondroitin sulfate antibodies. There are homologous tissues to the endosternite cartilage in other arthropods. The embryos of Limulus polyphemus express ColA and hyaluronan in the gill cartilage and the endosternite, which indicates that these tissues are fibrillar-collagen-based cartilage. The endosternite cartilage forms close to Hh-expressing ventral nerve cords and expresses ColA and SoxE. This is also seen in gill cartilage tissue.

Sabellid polychaetes

The Sabellid polychaetes have cartilage tissue with cellular and matrix specialization supporting their tentacles. They present two distinct extracellular matrix regions. These regions are an acellular fibrous region with a high collagen content, called cartilage-like matrix, and a collagen lacking highly cellularized core, called osteoid-like matrix. The cartilage-like matrix surrounds the osteoid-like matrix. The amount of the acellular fibrous region is variable. The model organisms used in the study of cartilage in sabellid polychaetes are Potamilla sp and Myxicola infundibulum.