Transcriptional regulation of AQP-8, a Caenorhabditis elegans aquaporin exclusively expressed in the excretory system, by the POU homeobox transcription factor CEH-6.
Due to the ever changing environmental conditions in soil, regulation of osmotic homeostasis in the soil-dwelling nematode Caenorhabditis elegans is critical. AQP-8 is a C. elegans aquaporin that is expressed in the excretory cell, a renal equivalent tissue, where the protein participates in maintaining water balance. To better understand the regulation of AQP-8, we undertook a promoter analysis to identify the aqp-8 cis-regulatory elements. Using progressive 5' deletions of upstream sequence, we have mapped an essential regulatory region to roughly 300 bp upstream of the translational start site of aqp-8. Analysis of this region revealed a sequence corresponding to a known DNA functional element (octamer motif), which interacts with POU homeobox transcription factors. Phylogenetic footprinting showed that this site is perfectly conserved in four nematode species. The octamer site's function was further confirmed by deletion analyses, mutagenesis, functional studies, and electrophoretic mobility shift assays. Of the three POU homeobox proteins encoded in the C. elegans genome, CEH-6 is the only member that is expressed in the excretory cell. We show that expression of AQP-8 is regulated by CEH-6 by performing RNA interference experiments. CEH-6's mammalian ortholog, Brn1, is expressed both in the kidney and the central nervous system and binds to the same octamer consensus binding site to drive gene expression. These parallels in transcriptional control between Brn1 and CEH-6 suggest that C. elegans may well be an appropriate model for determining gene-regulatory networks in the developing vertebrate kidney.
Mah
Allan K
AK
Department Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada.
Armstrong
Kristin R
KR
Chew
Derek S
DS
Chu
Jeffrey S
JS
Tu
Domena K
DK
Johnsen
Robert C
RC
Chen
Nansheng
N
Chamberlin
Helen M
HM
Baillie
David L
DL
D000818:Animals; D020346:Aquaporins / Q000378:metabolism* / Q000502:physiology; D001483:Base Sequence; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism / Q000502:physiology*; D019295:Computational Biology; D017931:DNA Primers / Q000737:chemistry; D018398:Homeodomain Proteins / Q000378:metabolism / Q000502:physiology*; D007668:Kidney / Q000378:metabolism; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D050809:POU Domain Factors / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic
D020346:Aquaporins; D029742:Caenorhabditis elegans Proteins; C423385:Ceh-6 protein, C elegans; D017931:DNA Primers; D018398:Homeodomain Proteins; D009419:Nerve Tissue Proteins; D050809:POU Domain Factors; D014157:Transcription Factors; C108330:aquaporin 8; C074065:Pou3f3 protein, mouse