GBF-dependent family genes morphologically suppress the partially active Dictyostelium STATa strain

Abstract

Transcription factor Dd-STATa, a functional Dictyostelium homologue of metazoan signal transducers and activators of transcription proteins, is necessary for culmination during development. We have isolated more than 18 putative multicopy suppressors of Dd-STATa using genetic screening. One was hssA gene, whose expression is known to be G-box-binding-factor-dependent and which was specific to prestalk A (pstA) cells, where Dd-STATa is activated. Also, hssA mRNA was expressed in pstA cells in the Dd-STATa-null mutant. At least 40 hssA-related genes are present in the genome and constitute a multigene family. The tagged HssA protein was translated; hssA encodes an unusually high-glycine-serine-rich small protein (8.37 kDa), which has strong homology to previously reported cyclic-adenosine-monophosphate-inducible 2C and 7E proteins. Overexpression of hssA mRNA as well as frame-shifted versions of hssA RNA suppressed the phenotype of the partially active Dd-STATa strain, suggesting that translation is not necessary for suppression. Although overexpression of prespore-specific genes among the family did not suppress the parental phenotype, prestalk-specific family members did. Although overexpression of the hssA did not revert the expression of Dd-STATa target genes, and although its suppression mechanism remains unknown, morphological reversion implies functional relationships between Dd-STATa and hssA.

Cell-type specific RNA-Seq reveals novel roles and regulatory programs for terminally differentiated Dictyostelium cells

“…The cup-specific late expressed genes contained many members of the hssA/7E/2C family [ 24 ], which are also the most highly expressed genes in the set. The hssA genes are around 213 bp in size, with a 13 bp first exon and ~ 200 bp second exon.…”

Dictyostelium Finds New Roles to Model

“…Although valuable results have been obtained using a Dictyostelium cDNA expression library (Robinson and Spudich 2000;Shimada and Kawata 2007;Shimada et al 2008), the library is very unlikely to contain full-length sequences representing all the less highly transcribed genes. The alternative approach of genomic DNA complementation has never been made to work, probably because of the difficulty of amplifying representative genomic Dictyostelium DNA libraries in E. coli.…”

The GATA transcription factor gene gtaG is required for terminal differentiation in Dictyostelium

“…The hssA gene, which encodes a 93-amino-acid polypeptide, was originally identified as a high-copy suppressor of the Dd-STATa mutant. However, its expression is independent of Dd-STATa and dependent on GbfA (Iranfar et al, 2006;Shimada et al, 2008). Dd-STATa was overexpressed after 12 h of development in the gtaG − mutant (dstA in Fig.…”

“…First, many DdSTATa-dependent transcripts, including ecmF, ecmJ and aslA (Shimada et al, 2004), are gtaG-dependent. Second, gtaG is essential for the expression of several genetic suppressors of the DdSTATa-defective phenotype (Shimada et al, 2008), including some members of the hssA/7E/2C family. Third, dstA − cells fail to synergize with gtaG − cells in mixing experiments.…”