Cytochemical investigations on tunic morphogenesis in the sea peach Halocynthia papillosa (Tunicata, Ascidiacea) 2: demonstration of proteins

Abstract

In a previous paper, cellulose fibres were demonstrated in the larval, the metamorphosing, and the juvenile tunics. In this paper we used cytochemical methods and X-ray microanalysis to obtain additional information on tunic morphogenesis in Halocynthia papillosa. The chemical composition of the tunic evolves with its structural complexity. The larval and juvenile fibres are shown to be structurally and chemically different. While neither proteins nor glycosaminoglycans seem to be associated with the larval fibres, the juvenile fibres consist of a cellulose core wrapped in a sheath of tannophilic proteins. Patches of glycosaminoglycans line their longitudinal axes. In the course of metamorphosis, the cuticle undergoes profound modifications in regions of spine morphogenesis. Granular material that was previously called fibro-granular material (Lübbering et al., 1993) is essential to the formation of cuticular plates and spines. During metamorphosis, this material accumulates in epidermal granules and is discharged into the tunic. It crosses the fundamental layer of the tunic and reaches the cuticle. Our results strongly suggest that this material consists of proteins rich in cysteine and hydrophobic amino acids.