Fig. 4. Formation of the fruiting body. (A) The slug contains a pre-pattern that presages culmination. The pstAB cells form an inverted cone structure within the slug tip. These cells mark the future entrance to the stalk tube and are the first cells to enter the stalk. As culmination proceeds, they embed into the basal disc. When development passes directly from mound to culmination, the basal disc is formed from the pstB population. During slug migration, pstB cells are lost and re-differentiate from the anterior-like cells (ALC). The ALC are also a source of the pstO cells. During culmination, pstO cells differentiate into pstA cells and then into stalk cells within the stalk tube. The upper and lower cup structures form from pstO and pstB populations, respectively. (B) During culmination, the stalk tube forms a constriction just below its entrance. A transverse section of this region shows that the cells surrounding this stalk tube are connected by electron-dense adherens junctions (AJ) and actin filaments (AF). Reprinted by permission from Nature 408:727-731 copyright 2000 Macmillan Magazines Ltd.
