Chick embryo limb bud mesenchyme cells undergoing chondrogenesis in vitro were labeled with [3H] arachidonic acid and [14C] palmitic acid, and stimulated by mechanical means to convert a portion of their incorporated [3H] to radiolabeled compounds which co-chromatographed with authentic prostaglandins in the appropriate thin layer chromatography system. Chondrogenesis was (1) inhibited by concentrations of indomethacin or eicosa-5,8,11,14-tetraynoic acid which inhibited conversion of [3H] to prostaglandinlike compounds; and (2) stimulated by prostaglandin E2. We interpret these data to mean that (1) cells undergoing chondrogenesis in vitro are able to metabolize endogenous arachidonic acid to prostaglandins, and (2) synthesis of prostaglandinlike compounds is requisite to chondrogenesis in vitro.
This study correlates endogenous levels of cAMP and cGMP with their immunohistochemical localization during chondrogenic differentiation of C57B1/6J mouse limb mesenchyme in vivo and in vitro. A transient decrease in cGMP but not cAMP was found from days 12 to 13 in vivo correlating with early stages of chondrogenesis in the developing limb. Intracellular levels of both cAMP and cGMP in high density limb mesenchyme cultures increased 25% after 24 hr in culture when aggregate and nodule formation was detectable. When cells were seeded at different initial plating densities to delay the onset of aggregate and nodule formation, increased levels of intracellular cAMP correlated temporally with the appearance of nodules. Both cyclic AMP and cGMP were immunohistochemically localized in perichondrial cells and chondrocytes in vivo and in vitro. Therefore, (1) cAMP levels correlated temporally with the appearance of chondrogenic cells and (2) cAMP and cGMP were immunohistochemically localized to chondrogenic cells. These data indicate that fluctuations of both cAMP and cGMP levels may be involved in limb cartilage differentiation. Although increases in both nucleotides were found to correlate with the onset of chondrogenesis in vitro, in vivo data suggest that the amount of cAMP relative to cGMP rather than the absolute amount of an individual cyclic nucleotide may be more significant in modulating differentiation.
The XT-1-molecule, an adhesion-related differentiation antigen of male mouse germ cells, is a 34000 Mr glycoprotein with major charge isomer at pI 5·1 and is an integral component of the cell membrane. On large late pachytene spermatocyte, the molecule is present at a concentration of 2·5×103 molecules µm−2, which approximates HLA/ABC concentration on lymphocytes. By comparing the reactivity of four anti-XT-1 monoclonal antibodies, three of which elicit germ cell-germ cell adhesion, we have defined two distinct surface regions of the XT-1-molecule. The relationship of the XT-1-molecule with other known adhesion-related molecules and testicular antigens is discussed.
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