Spicule matrix protein LSM34 is essential for biomineralization of the sea urchin spicule.

Biomineralized skeletal structures are composite materials containing mineral and matrix protein(s). The cell biological mechanisms that underlie the formation, secretion, and organization of the biomineralized materials are not well understood. Although the matrix proteins influence physical properties of the structures, little is known of the role of these matrix proteins in the actual formation of the biomineralized structure. We present here results using an antisense oligonucleotide directed against a spicule matrix protein, LSM34, present in spicules of embryos of Lytechinus pictus. After injection of anti-LSM34 into the blastocoel of a sea urchin embryo, LSM34 protein in the primary mesenchyme cells decreases and biomineralization ceases, demonstrating that LSM34 function is essential for the formation of the calcareous endoskeletal spicule of the embryo. Since LSM34 is found primarily in a specialized extracellular matrix surrounding the spicule, it is probable that this matrix is important for the biomineralization process.