Partner specificity is essential for proper function of the SIX-type homeodomain proteins Sine oculis and Optix during fly eye development

Abstract

The development of the Drosophila visual system utilizes two members of the highly conserved Six-Homeobox family of transcription factor, Sine oculis and Optix. Although in vitro studies have detected differences in DNA-binding and interactions with some co-factors, questions remain as to what extent the activity for these two transcriptional regulators is redundant or specific in vivo. In this work, we show that the SoD mutation within the Six domain does not abolish DNA-protein interactions, but alters co-factor binding specificity to resemble that of Optix. A mutation in the same region of Optix alters its activity in vivo. We propose that the dominant mutant phenotype is primarily due to an alteration in binding properties of the Sine oculis protein and that distinct partner interactions is one important mechanism in determining significant functional differences between these highly conserved factors during eye development.

Dual transcriptional activities of SIX proteins define their roles in normal and ectopic eye development

“…7, rows 2 and 5). Our results showing that So binds to Eya is supported by data from yeast 2-hybrid and in vitro GST pull-down assays (Pignoni et al, 1997;Kenyon et al, 2005a;Kenyon et al, 2005b). However, our data demonstrating that Optix can interact with Eya stands in contrast to a report that failed to observe a genetic interaction between the two genes (Seimiya and Gehring, 2000) and a yeast 2-hybrid assay that used a truncated Optix protein (Kenyon et al, 2005a).…”

“…The evidence surrounding Drosophila Optix presents a slightly different picture. In directed yeast two-hybrid assays, a truncated version of Optix is capable of binding to Gro but not to Eya (Kenyon et al, 2005a;Kenyon et al, 2005b). Optix and Eya also do not functionally interact during the induction of ectopic eye development (Seimiya and Gehring, 2000;Salzer and Kumar, 2010).…”

Direct control of neurogenesis by selector factors in the fly eye:regulation ofatonalby Ey and So

“…Either the full-length So protein produced in S2 cells, or a GSTSo SixHD -fusion protein purified from Escherichia coli (Six and Homeobox domains) (Kenyon et al, 2005) were used. DNA probes were generated by PCR or by annealing of synthesized oligonucleotides, and were labeled using polynucleotide kinase (NEB) and [␥-32 P]ATP (Amersham).…”

Cell cycle regulation of the human Six1 homeoprotein is mediated by APCCdh1

“…Six1 protein represented by the light gray oval, can then be synthesized and bind to regulatory regions of its target genes during S and G 2 phases. Although Six1 is known to cooperate with cofactors (Kenyon et al, 2005), for simplicity only Six1 is shown in the diagram. Six1 exists as a phosphoprotein throughout the cell cycle, but is hyper-phosphorylated during mitosis, inhibiting its ability to bind DNA.…”