The POU protein Oct-6 is a nucleocytoplasmic shuttling protein

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.

Section: Discussionmentioning

confidence: 98%

Transcriptional Regulation of AQP-8, a Caenorhabditis elegans Aquaporin Exclusively Expressed in the Excretory System, by the POU Homeobox Transcription Factor CEH-6

Mah

Armstrong

Chew

et al. 2007

“…However, the dynamic behavior of Oct4 once imported into the nucleus is essentially unknown. In contrast, Oct6, another POU homeodomain transcription factor, is known to shuttle between the nucleus and cytoplasm (26). Thus, in the present study we analyzed the dynamic behavior of Oct4 and its role in the determi-nation of cell fate.…”

Section: Oct4 Is a Member Of The Pou Family Of Transcription Factors mentioning

confidence: 99%

“…Oct6, another member of POU transcription factor family, is exported from the nucleus by the nuclear export factor Crm1/ exportin 1 (26). Thus, we subsequently examined whether Oct4 is also exported by Crm1.…”

Section: Oct4mentioning

confidence: 99%

Differential Role for Transcription Factor Oct4 Nucleocytoplasmic Dynamics in Somatic Cell Reprogramming and Self-renewal of Embryonic Stem Cells

Oka

Moriyama²,

Asally³

et al. 2013

Background:The spatiotemporal dynamic behavior of Oct4 remains largely unknown. Results: Oct4 is a nucleocytoplasmic shuttling protein, and Oct4 mutants with biased nucleocytoplasmic localization show limited potential for cellular reprogramming. Conclusion: An appropriate nuclear retention of Oct4 is critical for cellular reprogramming but not for the self-renewal of ES cells. Significance: Our findings will provide novel insight into the role of Oct4 during cellular reprogramming.

“…Some homeodomain-containing proteins (Vsx1, Chx10, Otx1, Otx2, Oct6, and Prospro) shuttle in and out of the nucleus (71)(72)(73)(74)(75). The localization of most of these proteins is sensitive to leptomycin B, suggesting a Crm1-mediated export pathway (76).…”

Section: Discussionmentioning

confidence: 99%

The Roles of Multiple Importins for Nuclear Import of Murine Aristaless-related Homeobox Protein

Lin

Cai

et al. 2009

Nuclear import of proteins with nuclear localization signals (NLSs) is mediated by shuttling carriers, the importins. Some cargoes display more than a single NLS, and among these are homeodomain proteins such as Arx, which is critical for development of multiple tissues. Arx has two functional NLSs. The present studies show that several pathways can import Arx via its NLS2, which is within its DNA binding homeodomain. Using an in vitro nuclear import assay, we show that import of Arx via NLS2 can be mediated by importin ␤1, importin 9, or importin 13, with binding being strongest to importin ␤1. All binding is sensitive to RanGTP. Experiments based on precise domain deletions indicate that NLS2 binds imp␤1, imp9, and imp13 and includes both an importin binding subdomain and a regulatory subdomain with arginine residues being important for function. Moreover, Arx can be co-precipitated with these importins when NLS2 is present. Although nuclear import of Arx can be mediated by these three importin ␤s, importin ␤1 seems to play the major role judging from in vivo small interfering RNA ablations and the in vitro import assay. This is the first evidence to show the role of importin ␤1 in nuclear import of paired-type homeodomain proteins. We propose a novel and possibly quite general mechanism for nuclear import of paired-type homeodomain proteins which is critical for development.Precise nucleocytoplasmic distribution of the homeodomain superfamily of transcription factors is critical for development. Several studies have demonstrated that NLS activity resides within the 60-amino acid DNA binding homeodomain itself, which is composed of three helices (1, 2). The "paired type" subgroup of the superfamily is characterized by a set of highly conserved residues. There are 26 members of this subgroup in man. The aristaless-related homeobox (ARX) 4 protein, a paired-type homeodomain containing protein, is mutated in multiple human conditions (3-5). ARX is expressed most strongly in the brain (6) and is important for development of the forebrain, pancreas, and testis (7). Arx proteins are highly conserved (Fig. 1) and contain 562 amino acids (564 amino acids in mouse) with four poly(A) (alanine) tracts of variable length, a paired-type homeodomain, and a conserved "aristaless" domain (8). Endogenous Arx was found in the nucleus of some types of nerve cells (9, 10). Because Arx has a molecular mass larger than 60 kDa, its nuclear import is likely to be signal-dependent. Three putative basic NLSs in Arx have been proposed (8, 11): NLS1 from aa 82 to 89, BC1 from aa 327 to 334, and BC2 from aa 381 to 388 (Fig. 1). It is not clear whether or how these putative NLSs function in the nuclear localization of Arx.As for other trinucleotide-repeat-containing genes (12, 13), the first poly(A) tract can expand in Arx. Expansion of this tract or loss of the 3Ј aristaless domain in Arx are both associated with infantile spasms syndrome and mental retardation (14, 15). Moreover, expansion of the first poly(A) tract of Arx results in for...