Gradients in the expression of cell surface glycoproteins in a simple tissue, the Dictyostelium discoideum slug

Abstract

Gradients in diffusible morphogens have long been postulated to have a role in the establishment of polarity and pattern formation in developing animal embryos. In the cellular slime mould Dictyostelium discoideum, several morphogens have been described and their interactions and location in the multicellular 'slug' stage are being studied. Here we report that two cell surface antigens, which identify prespore and prestalk cells, respectively, are present at different levels on the surface of cells depending on their position within the slug. This is the first evidence of the existence of gradients in cell surface molecules in Dictyostelium discoideum tissues. The level of prespore glycoprotein PsA on the surface of prespore cells increased progressively along the length of the slug, so that the rear cells had the highest surface density of this glycoprotein. Since the pspA gene, which encodes PsA, is CAMPregulated, this raises the possibility that expression of PsA reflects an underlying morphogenetic cAMP gradient. The level of the MUD9 antigen, which is prestalk-enriched, decreased on the surface of prestalk cells towards the rear of the slug. As this correlated with a decrease in size of these cells along the length of the slug, it is possible that the surface density of this antigen is approximately constant. We have also identified a population of prestalklike cells that lack both the PsA glycoprotein and the MUD9 antigen. These cells primarily occurred in the posterior of the slug and could represent the population of cells that form the basal disc.

Recombinant Prespore‐Specific Antigen from Dictyostelium discoideum is a β‐sheet Glycoprotein with a Spacer Peptide Modified by O‐linked N‐acetylglucosamine

“…Browne and Williams (1993) have shown that PsA is unevenly distributed within the slug, prespore cells at the posterior end of the slug having greater levels of PsA than those in the anterior. Transcription of the pspA gene, which encodes PsA, is CAMP-dependent (Barklis and Lodish, 1983), which suggests the possible presence of morphogenetic gradients of CAMP within the slug (Browne and Williams, 1993).…”

Dictyostelium discoideum as Expression Host: Isotopic Labeling of a Recombinant Glycoprotein for NMR Studies

“…This glycoprotein is the predominant cell surface protein during slug phase of the D. discoideum life cycle, and the molecule's emergence on the cell surface signals the initiation of organized multicellular tissue (11). There has recently been a substantial increase in structural information concerning proteins involved in cell adhesion, with several types of three-dimensional folds now defined from among the clearly identifiable and recurring protein modules (12)(13)(14). It remains to be seen where PsA fits within the existing classes of cell surface molecular structures.…”

NMR assignment of prespore specific antigen—a cell surface adhesion glycoprotein from Dictyostelium discoideum

“…A model system in which these cellular processes has been particularly well studied is the eukaryote Dictyostelium discoideum (Coates and Harwood 2001). This report concerns pre-spore specific antigen (PsA), the most abundant cell surface protein of D. discoideum in the multicellular stage of its life cycle, where it occurs spread in a spatial gradient across the slug tissue (Browne and Williams 1993).…”