THE SEA-URCHIN LARVA, A SUITABLE MODEL FOR BIOMINERALIZATION STUDIES IN-SPACE (IML-2 ESA BIORACK EXPERIMENT 24-F URCHIN)

By the ESA Biorack 'F-24 urchin' experiment of the IML-2 mission, for the first time the biomineralisation process in developing sea urchin larvae could be studied under real microgravity conditions. The main o bjectives were to determine whether in microgravity the process of ske leton formation does occur correctly compared to normal gravity condit ions and whether larvae with differentiated skeletons do 'de-mineralis e'. These objectives have been essentially achieved, Postflight studie s on the recovered 'sub-normal' skeletons focused on qualitative, stat istical and quantitative aspects. Clear evidence is obtained that the basic biomineralisation process does actually occur normally in microg ravity, No significant differences are observed between flight and gro und samples. The sub-normal skeleton architectures indicate, however, that the process of positioning of the skeletogenic cells (determining primarily shape and size of the skeleton) is particularly sensitive t o modifications of environmental factors, potentially including gravit y. The anatomical heterogenity of the recovered skeletons, interpreted as long term effect of an accidental thermal shock during artificial egg fertilisation (break of climatisation at LSSF), masks possible eff ects of microgravity, No pronounced demineralisation appears to occur in microgravity; the magnesium component of the skeleton seems yet les s stable than the calcium, On the basis of these results, a continuati on of biomineralisation studies in space, with the sea urchin larva as model system, appears well justified and desirable.