May play a role in the regulation or execution of skeletal growth. Secreted to the skeletal compartment and accumulates predominantly at the advancing mineralizing surface of the spicule tips. As the spicules elongate PM27 protein disappears from the more mature mid-shaft regions. May be concentrated at the mineral-nonmineral interface, rather than within the spicule matrix. Expressed specifically in the micromere/primary mesenchyme cells (PMC) lineage. Produced uniformly and exclusively by PMCs through the early prism stage and this specificity is further restricted during skeletogenesis to a subpopulation of PMCs associated with the growing tips of the spicules. Appears at the mesenchyme blastula stage. The repetitive domain may provide a calcite binding matrix.