Dev Growth Differ
December 1, 2006;
Expression and promoter analysis of Xenopus DMRT1 and functional characterization of the transactivation property of its protein.
The doublesex and mab-3-related transcription factor 1 (DMRT1
) is involved in testis
formation in a variety of vertebrates. In the teleost fish, Medaka, DMY/DMRT1Y on the Y chromosome, a duplicate of the autosomal DMRT1
gene, is characterized as a sex-determining gene. We report here the characterization of the Xenopus DMRT1
genes. Reverse transcription-polymerase chain reaction (RT
-PCR) analysis revealed that X. laevis DMRT1
was expressed throughout the embryo
during early development and was restricted to the primordial gonads after embryogenesis. Whole-mount in situ hybridization analysis of the gene confirmed its specific expression in the primordial gonads. To study the transcriptional control of DMRT1
gene expression, we isolated the predicted promoter region of X. tropicalis DMRT1
using databases for this species. Analysis of transgenic tadpoles with a green fluorescence protein (GFP) reporter showed that approximately 3 kb of the 5''-flanking sequence of the DMRT1
gene was implicated in DMRT1
expression in the primordial gonads. We also showed that the C-terminal region of DMRT1
functioned as a transactivation domain in cultured cells, by a luciferase reporter assay using fusion proteins with the DNA-binding domain of GAL4
. These findings suggest that DMRT1
functions as an activator of one or more genes involved in sex determination or gonadal differentiation.
Dev Growth Differ
[+] show captions
Fig. 1. Structure of Xenopus
DMRT1. (A) Amino acid sequence
comparison among X. laevis, X.
tropicalis, Rana rugosa and human
DMRT1. The sequence of X. laevis
DMRT1 we obtained was identical
to that reported by Osawa et al.
(2005). The Rana and human sequences
of DMRT1 were reported
by Shibata et al. (2002) and
Raymond et al. (1998), respectively.
The protein sequence of
X. tropicalis DMRT1 was predicted
by analyses of the X. tropicalis
EST and genome databases. Multiple
alignments were performed
using the ClustalW program.
Identical amino acids to X. laevis
DMRT1 are shown in white against
black. Xl, Xenopus laevis; Xt,
Xenopus tropicalis; R, Rana rugosa;
H, human. (B) Predicted intronexon
structure of the X. tropicalis
DMRT1 gene. Detailed information
about the genome and EST
databases and their analyses is
provided in the Results section.
Fig. 2. Expression of DMRT1 during development in X. laevis.
(A) Reverse transcription-polymerase chain reaction (RT-PCR)
analysis of DMRT1 and elongation factor-1α (EF-1α) and
ornithine decarboxylase (ODC) as a control in unfertilized eggs
and embryos from stage (st.) 2-52. Each sample contained
0.25 μg of total RNA. L, H, P, M and G show liver, heart,
pronephros, mesonephros and primordial gonads, respectively.
(B) Specific expression of DMRT1 in the primordial gonad.
Whole-mount in situ hybridization using the antisense or sense
RNA probe for DMRT1 (nucleotides 598–1287) was performed
in tadpoles at stage 52 during sex determination. f and h show
forelimb and hindlimb. Scale bars, 0.5 mm.
Fig. 3. Promoter reporter analysis
of X. tropicalis DMRT1 in transgenic
animals. Decondensed sperm
nuclei were introduced into unfertilized
eggs of X. laevis together
with a plasmid bearing the green
fluorescence protein (GFP) gene
downstream of about 3 kb of the
5′-flanking sequence of X. tropicalis
DMRT1. GFP expression was
observed by a stereoscopic fluorescence
microscope. Typical GFP
expression in embryos at stage
(st.) 17 and 30 (A) and in tadpoles
at stage 52 (B) are shown. Scale
bars, 0.5 mm.
Fig. 4. Transactivation activity of the C-terminal region of X. laevis DMRT1. (A) In vitro transcription/translation was carried out using
<35S>-methionine and pcDNA3 FLAG-GAL4BD, pcDNA3 FLAG-GAL4BD-xDMRT1(full), pcDNA3 FLAG-GAL4BD-xDMRT1(1–134), or
pcDNA3 FLAG-GAL4BD-xDMRT1(130–334), and the <35S>-labeled proteins were detected by sodium dodecyl sulfatepolyacrylamide
gel electrophoresis (SDS-PAGE) and autoradiography. (B) P19 cells were transfected with 0.2 μg of the GAL4-
responsive luciferase reporter plasmid, pFR-luc, and 10 ng or 30 ng of effector plasmid encoding a fusion protein with the
DNA-binding domain of GAL4 (pcDNA3 FLAG-GAL4BD, pcDNA3 FLAG-GAL4BD-xDMRT1(full), pcDNA3 FLAG-GAL4BD-xDMRT1(1–
134), or pcDNA3 FLAG-GAL4BD-xDMRT1(130–334)), as indicated. The Renilla luciferase plasmid pRL-SV (5 ng) was used as a control
for transfection efficiency in each experiment. Twenty-four hours after transfection, the luciferase activities were measured by a dual
luciferase reporter system. Data represent the mean ± SE from three independent experiments.