Changes in the types of collagen synthesized during chondrogenesis of the mouse otic capsule

Abstract

We have investigated the temporal relationship between the morphological differentiation of the mouse otic capsule and the pattern of collagen synthesis by mouse otocyst-mesenchyme complexes labeled in vitro. In 10.5- to 12-day embryos the mesenchyme surrounding the otocyst was loosely organized except for a few lateroventral condensations; explants from these embryos synthesized only small amounts of collagen. Collagen synthesis by whole explants increased by more than 50% between 12 and 13 days concomitant with metachromatic staining of the lateral periotic mesenchyme. Cartilage specific type II collagen was the predominant collagen synthesized by these explants as confirmed by SDS-PAGE, densitometry, CNBr cleavage, and V8 protease digestion. This biochemical expression of the cartilage phenotype preceded morphologic recognition of otic capsular cartilage by almost 2 days. Type II collagen synthesis continued to increase and predominate through Day 16 of gestation by which time the otic labyrinth was surrounded by mature cartilage. The minor cartilage collagen chains, 1α, 2α, and 3α, first appeared on different days of gestation. The 1α, and 3α chains were synthesized by explants from 11-day embryos while the 2α chain appeared during Day 13, just before overt differentiation of mature cartilage. These results suggested that the 1α, 2α, and 3α chains may not form heterotrimers containing all three chains and that synthesis of the 2α chain may be associated with stabilization of the cartilaginous matrix. Comparison of these data with the patterns of collagen production by mutant, diseased, or experimentally manipulated inner ear tissues may provide insights into the molecular basis of chondrogenic tissue interactions.