Inversion in Volvox tertius: the effects of con A
During the development of Volvox tertius spheroids, a single-celled gonidium enlarges and undergoes multiple incomplete cleavages to give an embryo which is ‘inside-out’ with respect to the adult organism. A morphogenetic movement, termed ‘inversion’, turns this hollow ball of cells ‘inside-out’ through a hole, the phialopore. In V. tertius this phialopore possesses 4 inwardly directed lips. Normal inversion was studied in vitro in slide chambers and involved cell-shape changes accompanied by the production of pseudopodia and the bending backwards of the phialopore lips. 100 micrograms/ml Con A specifically and reversibly blocked inversion. Despite the inhibitory effect on cell division, the blocking of inversion was not due to the blocking of the last cell division some 50–100 min prior to inversion. Neither did the first cell-shape change from pear- to spindle-shape appear blocked. A feature of inhibition by Con A was the enhanced production of pseudopodia by embryos blocked at inversion, and the abnormal production of pseudopodia by embryos blocked at earlier stages. Non-inverting embryos showed internal flagella. We suggest that the Con A block to inversion, which may be reversed by alpha-methyl mannoside, arises from the prevention of backwards-bending of the phialopore lips. Fluorescein-isothiocyanate-Con A bound to embryo and cell coat, ane more strongly to the embryo at pre-inversion. SDS-polyacrylamide gel analysis of proteins isolated from embryos showed 4 glycoprotein bands, but Con A binding to these bands could not be demonstrated.