Chick alpha-tectorin : molecular cloning and expression during development and regeneration in the avian inner ear.
The avian and mammalian tectorial membranes both contain two non-collagenous
glycoproteins, a- and ß-tectorin. To determine whether variations in the primary sequence
of the chick and mouse a-tectorins account for differences in subunit composition and
matrix structure of the tectorial membranes in these two species, the cDNA for chick atectorin
was cloned and sequenced. The derived amino acid sequence was found to have
73% identity with mouse a-tectorin, suggesting that the tectorins are highly conserved
proteins. The central region of chick a-tectorin contains fewer potential N-glycosylation
sites than that of mouse a-tectorin and is cleaved at two additional sites. The extra
glycosylation sites in the mouse sequence may help occlude sites of proteolytic attack. In
situ hybridisation and northern blot analysis indicate that the spatial and temporal patterns
of chick a- and ß-tectorin mRNA expression in the inner ear are different, suggesting that
the two tectorins may each form homomeric filaments.
Early functional recovery in the chicken after sound damage has been attributed to the
rapid regeneration of the tectorial membrane. In situ hybridisation indicates that both aand
ß-tectorin mRNAs are upregulated in the sound damaged basilar papilla. The
regenerated tectorial membrane contains both a and ß-tectorin proteins. In order to
understand how the tectorin genes are regulated during development and regeneration, the
upstream non-coding region of the ß-tectorin genes from mouse and chicken were
compared in an attempt to identify potential regulatory elements. DNA sequence
alignments of the chick and mouse ß-tectorin upstream sequence show low identity,
suggesting that the chick and mouse ß-tectorin promoters have not remained functionally
conserved throughout evolution.