Abstract
Proteoglycans and their associated glycosaminoglycans can bind growthfactors, integrin and non-integrin cell surface molecules, enzymes, proteaseinhibitors and other extracellular matrix components including fibronectin,laminin and tenascin. We studied the expression and spatiotemporaldistribution of versican and CD44 by RT-PCR and immunofluorescence inthe chick embryo from the morula stage (stage XI-XII) to early organogenesis(stage HH16+, 28-29 somites). We also studied the versican and CD44 roleby using blocking antibodies in the early chick embryo.Versican is a chondroitin sulfate proteoglycan that binds growth factorsand interacts with various extracellular matrix proteins and cell surfacemolecules including the CD44. Combined RT-PCR and immunohistochemistrydemonstrated the expression of versican as early as the morula stage.Interestingly, we detected splice variants of versican at the morula stage, andtheir expression was developmentally regulated. The presence of versicanmRNA at ...
Proteoglycans and their associated glycosaminoglycans can bind growthfactors, integrin and non-integrin cell surface molecules, enzymes, proteaseinhibitors and other extracellular matrix components including fibronectin,laminin and tenascin. We studied the expression and spatiotemporaldistribution of versican and CD44 by RT-PCR and immunofluorescence inthe chick embryo from the morula stage (stage XI-XII) to early organogenesis(stage HH16+, 28-29 somites). We also studied the versican and CD44 roleby using blocking antibodies in the early chick embryo.Versican is a chondroitin sulfate proteoglycan that binds growth factorsand interacts with various extracellular matrix proteins and cell surfacemolecules including the CD44. Combined RT-PCR and immunohistochemistrydemonstrated the expression of versican as early as the morula stage.Interestingly, we detected splice variants of versican at the morula stage, andtheir expression was developmentally regulated. The presence of versicanmRNA at the morula stage may indicate that it is of oogenetic origin. Versicanfluorescence was strong in the epiblast and the hypoblast at the late blastulastage (XIII). At stage HH3+ (intermediate streak), versican expression wasintense in the cells ingressing through the primitive streak and the migratingmesenchymal cells which will form the mesoderm and endoderm. By thedefinitive streak stage (HH4), versican fluorescence was intense in the cellsingressing through the primitive streak and in the mesenchymal cells thathave already started to form the mesoderm and endoderm. At stage HH8 (4somite pairs), versican expression was strong in the neural plate, theelevated neural folds and the ectoderm neighboring the neural folds. At stageHH12 (16 somite pairs), versican fluorescence was intense in the neural tubeand its adjacent ectoderm, the neural crest cells, the somite and in themesonephros and in the adjacent lateral mesoderm that will form themesonephric tubules. Later in development, versican fluorescence wasintense in the diencephalon, the optic stalk, mesencephalon, myelencephalon.Versican fluorescence was also intense in the dorsal mesocardium,myocardium and endocardium, dorsal aorta and aortic arches, in themyotome and sclerotome in somites, gut and in the extracellular matrix ofembryonic cavities. Inhibition of the function of versican by blockingantibodies showed that versican is crucial for the neural tube closure, neuralcrest migration, formation of the heart tube, for the architecture of embryoniccavities and consequently tissue and organ morphogenesis.CD44 is a transmembrane part-time proteoglycan and the main receptorfor hyaluronan. We detected CD44 protein even at the morula stage. Thepresence of high levels of CD44 mRNA at the morula stage indicated that thisis an oogenetic mRNA. CD44 fluorescence was strong in the epiblast cells,especially those neighboring the blastocoele, and in the hypoblast at the lateblastula stage (XIII). At stage HH3+, during gastrulation, CD44 was expressedstrongly in the epiblast cells, in mesenchymal cells and in endoderm cells. Atstage HH8 (4 somite pairs), strong CD44 expression was detected in theneural plate and neural folds and their adjacent ectoderm and this expressionpattern was similar to that of versican. Later in development, CD44expression was intense in the diencephalon, optic stalks, mesencephalon,myelencephalon, metencephalon, auditory vesicles and the neural crest cellsmigrating towards the auditory vesicle and the neural tube. CD44fluorescence was also intense in the dorsal mesocardium, myocardium,endocardium, aortae and aortic arches, sclerotome and myotome in somites,mesonephros, liver, gut and in the migrating neural crest cells that will formthe sympathetic and enteric ganglia. Inhibition of CD44 function by blockingantibodies showed that CD44 is crucial for the architecture of the embryoniccavities such as the brain lumen, neural tube closure, neural crest cellmigration, cardiac and cardiovascular formation and somite morphogenesis.Our results showed a synergistic role of CD44 and versican during thedevelopment of the early embryo.
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