A new Dictyostelium prestalk cell sub-type

Abstract

The mature fruiting body of Dictyostelium consists of stalk and spore cells but its construction, and the migration of the preceding slug stage, requires a number of specialized sub-types of prestalk cell whose nature and function are not well understood. The prototypic prestalk-specific gene, ecmA, is inducible by the polyketide DIF-1 in a monolayer assay and requires the DimB and MybE transcription factors for full inducibility. We perform genome-wide microarray analyses, on parental, mybE− and dimB− cells, and identify many additional genes that depend on MybE and DimB for their DIF-1 inducibility. Surprisingly, an even larger number of genes are only DIF inducible in mybE− cells, some genes are only inducible in DimB− cells and some are inducible when either transcription factor is absent. Thus in assay conditions where MybE and DimB function as inducers of ecmA these genes fall under negative control by the same two transcription factors. We have studied in detail rtaA, one of the MybE and DimB repressed genes. One especially enigmatic group of prestalk cells is the anterior-like cells (ALCs), which exist intermingled with prespore cells in the slug. A promoter fusion reporter gene, rtaA:galu, is expressed in a subset of the ALCs that is distinct from the ALC population detected by a reporter construct containing ecmA and ecmB promoter fragments. At culmination, when the ALC sort out from the prespore cells and differentiate to form three ancillary stalk cell structures: the upper cup, the lower cup and the outer basal disk, the rtaA:galu expressing cells preferentially populate the upper cup region. This fact, and their virtual absence from the anterior and posterior regions of the slug, identifies them as a new prestalk sub-type: the pstU cells. PstU cell differentiation is, as expected, increased in a dimB− mutant during normal development but, surprisingly, they differentiate normally in a mutant lacking DIF. Thus genetic removal of MybE or DimB reveals an alternate DIF-1 activation pathway, for pstU differentiation, that functions under monolayer assay conditions but that is not essential during multicellular development.

Cell signaling during development of Dictyostelium

“…However, rather than inducing expression, it appears to repress it (Zhukovskaya et al, 2006). In response to DIF-1 DimB appears to act as an inducer for some genes and as a repressor for other genes (Yamada et al, 2010). Two other DNA binding proteins, STATc and GataC, respond to addition of DIF-1 by rapid entry into the nucleus where they affect differentiation of PstO and PstB cells (Fukuzawa, Abe and Williams, 2003; Keller and Thompson, 2008; Fukuzawa, 2011).…”

eIF2α Kinases Regulate Development through the BzpR Transcription Factor in Dictyostelium discoideum

“…Upper cup cells are derived from ALCs as are lower cup and basal disk cells [27], [28]. The lack of β-galactosidase in the latter two cell types suggest its production was confined to the recently identified PstU cells [29]. Normal production of BzpR in upper cup or PstU cells may explain the “droopy” sori phenotype of bzpR null cells, as upper cup cells have been shown to function in lifting the spore mass up the stalk [30].…”

Combinatorial cell-specific regulation of GSK3 directs cell differentiation and polarity in Dictyostelium

“…These terminally differentiated cells derive from non-committed prespore and prestalk precursors. The pioneering work of Williams, Kay, Firtel and others have shown that progenitors to both prestalk and prespore populations are heterogeneous (Gaudet et al, 2008;Williams, 2006;Yamada et al, 2010). Spatially restricted expression of gene patterns has been used to define very specific classes of prestalk cells (e.g.…”