The different components of a multisubunit cell number-counting factor have both unique and overlapping functions

Debra A. Brock, R. Diane Hatton, Dan Victor Giurgiutiu, Brenton Scott, Robin Ammann, Richard H. Gomer

Research output: Contribution to journalArticlepeer-review

33 Scopus citations


Dictyostelium aggregation streams break up into groups of 103 to 2×104 cells. The cells sense the number of cells in a stream or group by the level of a secreted counting factor (CF). CF is a complex of at least 5 polypeptides. When the gene encoding countin (one of the CF polypeptides) was disrupted, the cells could not sense each other's presence, resulting in non-breaking streams that coalesced into abnormally large groups. To understand the function of the components of CF, we have isolated cDNA sequences encoding a second component of CF, CF50. CF50 is 30% identical to lysozyme (but has very little lysozyme activity) and contains distinctive serine-glycine motifs. Transformants with a disrupted cf5O gene, like countin- cells, form abnormally large groups. Addition of recombinant CF50 protein to developing cf5O- cells rescues their phenotype by decreasing group size. Abnormalities seen in aggregating countin- cells (such as high cell-cell adhesion and low motility) are also observed in the cf5O- cells. Western blot analysis of conditioned medium sieve column fractions showed that the CF50 protein is present in the same fraction as the 450 kDa CF complex. In the absence of CF50, secreted countin is degraded, suggesting that one function of CF50 may be to protect countin from degradation. However, unlike countin- cells, cf5O- cells differentiate into an abnormally high percentage of cells expressing SP70 (a marker expressed in a subset of prespore cells), and this difference can be rescued by exposing cells to recombinant CF50. These observations indicate that unlike other known multisubunit factors, CF contains subunits with both overlapping and unique properties.

Original languageEnglish (US)
Pages (from-to)3657-3668
Number of pages12
Issue number15
StatePublished - Aug 1 2002
Externally publishedYes


  • Cell population size
  • Counting factor
  • Dictyostelium discoideum

ASJC Scopus subject areas

  • Molecular Biology
  • Developmental Biology


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