ABSTRACT
In this study we investigate the gene regulatory functions of Drosophila Fish-hook (Fish), a high mobility group (HMG) Sox protein that is essential for embryonic segmentation. We show that the Fish HMG domain binds to the vertebrate Sox protein consensus DNA binding sites, AACAAT and AACAAAG, and that this binding induces an 85 degrees DNA bend. In addition, we use a heterologous yeast system to show that the NH2-terminal portion of Fish protein can function as a transcriptional activator. Fish directly regulates the expression of the pair rule gene, even-skipped (eve), by binding to multiple sites located in downstream regulatory regions that direct formation of eve stripes 1, 4, 5, and 6. Fish may function along with the Drosophila POU domain proteins Pdm-1 and Pdm-2 to regulate eve transcription, as genetic interactions were detected between fish and pdm mutants. Finally, we determined that Fish protein is expressed in a dynamic pattern throughout embryogenesis, and is present in nuclear and cytoplasmic compartments.
Subject(s)
DNA-Binding Proteins/physiology , Drosophila Proteins , Drosophila/genetics , Gene Expression Regulation, Developmental/physiology , High Mobility Group Proteins/physiology , Transcription Factors/physiology , Animals , Base Sequence , DNA Primers , Drosophila/embryology , SOX Transcription Factors , Transcriptional Activation/physiologyABSTRACT
We describe the isolation and analysis of the Drosophila fish-hook (fish) gene, which encodes a novel member of the SOX subgroup of High Mobility Group (HMG) domain proteins that exhibit similarity to the mammalian testis determining factor, SRY. The fish gene is initially expressed in a pair-rule-like pattern which is rapidly replaced by strong neuroectoderm expression. fish null mutants exhibit severe segmentation defects, including loss and/or fusion of abdominal denticle belts and stripe-specific defects in pair-rule and segment polarity gene expression.fish mutant embryos also exhibit loss of specific neurons, fusion of adjacent ventral nerve cord ganglia and aberrant axon scaffold organization. These results indicate an essential role for fish in anterior/posterior pattern formation and nervous system development, and suggest a potential function in modulating the activities of gap and pair-rule proteins.
