Quantitative in situ localization of tenascin-C alternatively spliced transcripts in the avian optic tectum.

PURPOSE Tenascin-C is an extracellular matrix glycoprotein found at sites of embryonic cell motility, including the developing visual system. Numerous alternatively spliced variants of tenascin-C have been identified, and these variants have distinctive properties in vitro. The purpose of this study was to use quantitative in situ hybridization to determine the relative abundance of transcripts encoding the alternatively spliced fibronectin type III repeats of tenascin-C in the embryonic avian optic tectum. METHODS Similarly sized DNA probes specific for sequences encoding the alternatively spliced repeats of tenascin-C were labeled with 35-S and applied to frozen sections of the E10 optic tectum. After determining the linear period of exposure, silver grain densities in the ventricular zone were calculated. RESULTS Densitometric analysis revealed that more than half of the total tenascin-C mRNAs expressed in the ventricular zone of the E10 optic tectum encode the variable fibronectin type III repeats "A," "AD1" and "D." Transcripts encoding other variable repeats were detectable, but at considerably lower levels. CONCLUSIONS The most abundant form of tenascin-C in the developing optic tectum has a molecular weight of 230 kDa. Most of this form contains the variable repeats "A," "AD1," and "D," a combination of fibronectin type III repeats that has previously been identified only in a tumor-derived cell line.