Orchestin, a calcium-binding phosphoprotein, is a matrix component of two successive transitory calcified biomineralizations cyclically elaborated by a terrestrial crustacean.

Orchestia cavimana is a crustacean that cyclically replaces its calcified cuticle during molting cycles in order to grow. Its terrestrial way of life requires storage of calcium during each premolt period, as calcareous concretions, in tubular diverticula of the midgut. During the postmolt period the stored calcium is reabsorbed and is translocated through the storage organ epithelium as calcified small spherules.

Characterization and spatiotemporal expression of orchestin, a gene encoding an ecdysone-inducible protein from a crustacean organic matrix.

We report the characterization of a new gene encoding an acidic protein named Orchestin. This protein is a component of the organic matrix of calcium storage structures (calcareous concretions) elaborated during the moulting cycles of the terrestrial crustacean Orchestia cavimana. The deduced molecular mass of Orchestin is estimated to be 12.

Premolt calcium secretion in midgut posterior caeca of the crustacean Orchestia: Ultrastructure of the epithelium.

Both structural and functional changes are observed within the posterior caeca (PC) of Orchestia during the molt cycle. During the intermolt period, there are two segments which are structurally different: a distal segment lined by type I epithelial cells and a proximal segment lined by type II cells. During molting, the PC cells are active in calcium turnover.

Fine structure of the midgut posterior caeca in the crustacean Orchestia in intermolt: Recognition of two distinct segments.

This study carried out on the posterior caeca of Orchestia in intermolt by means of light and electron microscopy shows that the diverticula of the midgut consist of two segments which are different from an anatomical point of view. The distal segment is in close relationship to the dorsal blood vessel, whereas the proximal segment, twice as long as the distal one, only touches the haemocoel. The cells of the distal segment are characterized by a brush border, some apical extrusions, a great number of ribosomes, rough endoplasmic reticulum, often associated with the mitochondria, the matrix of which is clear, high activity of the Golgi complexes, and a great development of extracellular channels.