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Cell Biology International (2001) 25, 147–155 (Printed in Great Britain)

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GIANT VACUOLES OBSERVED IN DICTYOSTELIUM DISCOIDEUM

Aidong Yuan^f1 and Catherine P. Chia

School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, NE, 68588-0118, U.S.A.

Abstract

Large intracellular vacuoles, >4μm in diameter and either round or oval-shaped, were observed infrequently in Dictyostelium discoideum amoebae of axenically-grown strain AX2 (only 1 in 106–108cells). These previously unreported single or multiple ‘giant’ vacuoles were more common, however, in newly germinated KAX3 cells (0.55% of the population) and AT-Kneg, a strain that lacks an esterase (0.47% of the population). A vacuolar H+-ATPase was enriched in their membranes of intracellular giant vacuoles, indicating that the vacuoles were related possibly to both endosomes and the contractile vacuole compartment. When monitored over time, giant vacuoles protruded from, and retracted back into cells under hyperosmotic conditions, suggesting an osmoregulatory role for these vacuoles. Some of the intracellular and protruded giant vacuoles harbored a fluid-phase marker, fluorescein-labeled dextran, implying a pinocytotic origin for the vacuoles.

Key words: Dictyostelium discoideum, giant vacuole, endosome, contractile vacuole, vacuolar H+-ATPase.

^f1To whom correspondence should be addressed: Aidong Yuan, PhD, School of Biological Sciences, University of Nebraska-Lincoln, 348 Manter Hall, P.O. Box 880118, Lincoln, NE 68588-0118, U.S.A. E-mail:dyuan@unlserve.unl.edu

Received 8 September 1999; accepted 16 May 2000