MINIREVIEW
Dmrt1 genes at the crossroads: a widespread and central
class of sexual development factors in fish
Amaury Herpin and Manfred Schartl
Physiological Chemistry I, University of Wuerzburg, Germany
Introduction
The phenomenon of two different sexes and conse-
quently the necessity to make a developmental decision
for an embryo to become male or female (the so-called
sex-determination process), and the further differentia-
tion of the whole organism into two distinct phenotypes,
are common throughout the animal, plant and fungi
kingdoms. Nevertheless, with respect to animals at least,
decades of elegant genetic studies have led to the global
picture that the gene-regulatory cascades triggering
sexual differentiation from Caenorhabditis elegans and
Drosophila to mammals bear little resemblance to each
other. Hence, although developmental cascades are
generally headed by highly conserved universal master
regulators that determine the developmental fate of
a cell lineage to a given tissue or organ during embryo-
genesis, all the evidence suggests that sex determination
might disobey the conventional rules of evolutionary
conservation. The common picture emerging here is that
the genes at the top of the cascade are not conserved,
whereas the downstream genes have homologues in a
much broader spectrum of species [1,2]. For example,
SRY, the male sex-determining gene of mammals, has
not been detected outside the eutherians (placental
mammals). Conversely, known downstream effectors
involved in gonadogenesis or gonadal differentiation

remarkable amount of descriptive expression data has been gathered in a
large variety of fish, particularly with respect to early gonadal differentia-
tion and sex change. This minireview aims at distilling the current knowl-
edge of fish dmrt1s, in terms of expression and regulation. It is shown how
gonadal identities correlate with dimorphic dmrt1 expression in gonochoris-
tic and hermaphroditic fish species. It is also described how sex steroid hor-
mones affect gonadal identity and dmrt1 expression. Emphasis is also given
to recent findings dealing with transcriptional, post-transcriptional, post-
translational and functional regulations of the dmrt1a ⁄ dmrt1bY gene pair
in medaka.
1010 FEBS Journal 278 (2011) 1010–1019 ª 2011 The Authors Journal compilation ª 2011 FEBS
Among the downstream candidate genes, a gene
family involved in sex differentiation in organisms as
phylogenetically divergent as C. elegans, Drosophila,
frogs, fish, birds, mammals and corals is the dmrt gene
family [5]. The prototype members of this group of
factors are the Drosophila doublesex (dsx) and Caenor-
habditis mab-3 genes. The Dmrt group of molecules is
characterized by a conserved DNA-binding motif
known as the Doublesex- and Mab-3-related (DM)
domain. Being a noncanonical cysteine-rich DNA-
binding motif, this domain has two highly intertwined
finger structures that chelate one zinc ion each, and
binds to the minor groove of the DNA [6]. Dmrts were
originally described to play important roles during sex
determination in flies and worms by regulating several
aspects of somatic sexual dimorphism. They were also
reported to be able to substitute for each other across
species, indicating that their function is possibly inter-
changeable and that sex determination in invertebrates

review) and because of the discovery of sex-chromo-
some-linked dmrt1s in other vertebrates (DM-W in
Xenopus [14] and dmrt1 in birds [15] for example),
it was tempting to speculate, at least for teleosts,
that dmrt1s might have a universal and top control
function during sex determination. However, the
absence of a dmrt1bY gene even in closely related
Medaka species ruled this out [16]. Nevertheless, factu-
ally it did not exclude Dmrt1, in general, as an impor-
tant conserved effector of testis development, including
spermatogenesis.
Despite the attention that Dmrt1 factors have
received, to date it has not been elucidated how
Dmrt1s mediate their activities and putative down-
stream targets have yet to be characterized [17]. How-
ever, a remarkable amount of descriptive expression
data has been gathered in a large number of different
fish species, particularly in the context of early gonadal
development, gonadal differentiation and sex change.
This minireview aims at distilling current knowledge
about the expression and regulation of dmrt1s in fish
towards a more general picture. Emphasis is also given
to recent findings dealing with transcriptional, post-
transcriptional, post-translational and functional regu-
lation of the dmrt1a ⁄ dmrt1bY gene pair in medaka.
Gonadal dmrt1 gene expression across
different fish species
An amazing variety of sex-determining systems is
found in fish. Although information is emerging about
sex determination in lampreys, sharks, rays and stur-

restricted expression territories are seen within the tes-
tis. With respect to a gonadal function of Dmrt1, its
early expression in the somatic part of the male gonad
anlage (Oreochromis niloticus [20] and Oryzias latipes
[21]) would infer a role correlated with Sertoli cell
lineage specification and subsequently during testicular
differentiation. The specific expression in spermatogo-
nia and spermatocytes reported for Clarias gariepinus
[18], Danio rerio [24] and Gadus morhua [25] are clearly
consistent with a role at some stage of spermatogenesis
in these species.
Another remarkable piece of information towards
the understanding of Dmrt1 function(s) is coming from
gonochoric fish that are annual breeders (Clarias
gariepinus [18], Oncorhynchus mykiss [27] and Silurius
meridionalis [29]). In these species, fish undergo a sea-
sonal pattern of gonadal resting and recrudescence
Table 1. Gonadal expression of dmrt1 genes across the fish kingdom.
Species
Gonadal
expression Expression levels
Expression
localization Methods Ref
Acanthopagrus schlegeli pA Testis Higher in mature testis n.i. PCR [30]
Acipenser fulvescens G Ovary and testis High in testes n.i. PCR [23]
Clarias gariepinus G Testis Ova-testis Spermatogonia,
spermatocytes
PCR, IC,
western blot
[18]

Oncorhynchus mykiss G Testis and ovary Higher in testes Differentiating testis PCR, Northern
blot
[27]
Oreochromis niloticus G Testis In sex-reversed testes Sertoli and epithelial cells
of the efferent duct
PCR, ISH [20]
Oryzias latipes G Dmrt1a: testis – Spermatogonial
supporting cells,
pre-Sertoli,
PCR, ISH, IC [21,54]
Dmrt1bY: testis – Sertoli cells and testicular
interstitial tubules
Paralichthys olivaceus G Testis – n.i. PCR [22]
Scaphirhynchus
platorynchus
G Testis and ovary Higher in testes n.i. PCR [28]
Sparus auratus pA Testis Decreases during
testicular involution
n.i. PCR [31]
Silurus meridionalis G Ovary and testis High in testes during
masculinization
n.i. PCR [29]
Takifugu rubripes G Testis and ovary High in testes Sertoli cells PCR, ISH [57]
Xiphophorus maculatus G Testis – Spermatogonia,
Sertoli cells
PCR, ISH [58]
G, gonochoric; pA, protandrous; pG, protogynous; TSD, temperature-dependent sex determination; n.i., not investigated; IC, immunocyto-
chemistry; ISH, in situ hybridization.
Sexual development factors in fish A. Herpin and M. Schartl
1012 FEBS Journal 278 (2011) 1010–1019 ª 2011 The Authors Journal compilation ª 2011 FEBS

genesis. Of note, in pejerrey (Odontesthes bonariensis),
a teleost with a temperature-dependant sex determina-
tion system, developmental expression of dmrt1 is
perfectly correlated with the rearing temperature (up at
male-determining temperatures and down at female-
determining temperatures) [26].
Dmrt1 expression in fish and other
vertebrates, what does it tell us?
In some fish species, dmrt1 expression is seen only in
somatic cells, whereas other fish have clearly additional
expression in the germ cell lineage (Table 1). This dif-
ference in cell types expressing dmrt1 might reflect spe-
cies-specific differences in testicular structure and
development. A dual dmrt1 cell lineage expression in
Sertoli and germ cells is the hallmark of mammalian
dmrt1s. Surprisingly, although mouse dmrt1 is detected
in the bipotential gonad, knockout male mice have
defects only during postnatal testis differentiation [35].
Although this observation might lead to the assump-
tion that germline expression is dispensable, condi-
tional dmrt1 inactivation in either the Sertoli cells or
the germ cells indicated that mouse Dmrt1 is indeed
required for radial migration of germ cells and survival
of gonocytes. It is also required autonomously for
proper Sertoli cell differentiation [36]. Hence, it is seen
that mouse Dmrt1 might not play a major role during
early testis differentiation, but rather appears to be
required later for male gonadal differentiation. Inter-
estingly, also expressed in the primordial gonads at the
time of sex determination, the Z-linked dmrt1 gene

both male and female gonadal expression was reported
for dmrt2 in medaka [39] and dmrt3 and -5 in zebrafish
[42,43]. This expression discrepancy regarding the
dmrt paralogues may indicate a possible functional
switch between those in different phylogenetic lineages.
Remarkably, when reported, non-dmrt1 gene expres-
sion generally occurs in developing germ cells (Table 2).
In terms of inferred function(s), this incidentally indi-
cates that paralogs of dmrt1 in fish, although obviously
not involved in the first steps of gonadogenesis, might
A. Herpin and M. Schartl Sexual development factors in fish
FEBS Journal 278 (2011) 1010–1019 ª 2011 The Authors Journal compilation ª 2011 FEBS 1013
be implicated in the later processes leading to the
proper development of germ cells.
Effects of sex steroid hormones on
gonadal identity and dmrt1 expression
Sex steroids have local, direct effects on germ cell
development, but also act as endocrine hormones to
influence other cell types and organs involved in sex
differentiation. This multilevel control is especially
complex in fish and involves a multitude of biochemi-
cal and physiological pathways to provide the neces-
sary plasticity for gonadal development (see [4] for
review). In that context, understanding the changes in
dmrt1 expression following steroid treatment is of
prime interest in order to link the molecular cellular
events with the extracellular hormonal signalling sys-
tem in gonad development.
Studies employing fish exposed to estrogens (or sub-
stances mimicking estrogen activities) are sparse but

appears that dmrt1 could be one of the major regulators
upstream of this enzyme in fish. It could be shown in
trout that masculinizing treatments (1,4,6-androstatri-
ene-3,17-dione) were inducing rapid and strong tran-
scriptional upregulation of testicular markers like
dmrt1, dax1 and pdgfra [46]. This upregulation was even
interpreted as an essential step required for active mas-
culinization. Into that direction, Dmrt1 and Dax1 have
recently been shown to directly downregulate cyp19a1a
promoter activity in the fish ovary [47,48]. Given the
abovementioned observation that estrogens repress male
differentiation it appears that, once initiated, factors of
the male pathway downregulate the hormone. Hence, a
feedback loop between dmrt1, cyp19a1a, and by implica-
tion the estrogen ⁄ androgen balance, becomes apparent.
Dmrt1 expression modulation upon steroid treatments
could then be a key effector of the induced gonadal
identity change (Fig. 1). Similarly, in chicken, it could
be shown that Dmrt1 also downregulates aromatase
expression [37]. Overall, it is now clear that, at least
in fish Dmrt1-regulating aromatase expression and by
implication the estrogen ⁄ androgen balance that would
also feedback (negatively or positively respectively) on
dmrt1 expression, creates a complex regulatory loop
combining transcriptional regulation with steroid hor-
monal activity (Fig. 1). The main question remaining is
Table 2. Other dmrt genes having gonadal expression in fish.
Genes Species Gonadal expression Expression in nongonadal tissues Ref
dmrt2 Oryzias latipes Testis and ovary Embryogenesis, somites,
pharyngeal arches and brain

In the medaka, which has XY–XX sex determination,
dmrt1bY, the duplicated copy of dmrt1a on the Y
chromosome was shown to be the dominant master
regulator of male development [8], similar to Sry in
mammals. Although many of the earliest cellular and
morphological events initiated by Sry have been char-
acterized, little is known about how the initial molecu-
lar activity of Sry is translated into cellular structure
and organ morphology. Interestingly, Dmrt1, the
ancestor of Dmrt1bY, is one of the downstream effec-
tors of Sry in the male pathway.
In medaka, the duplicated copy of dmrt1 has
acquired an upstream position in the sex-determining
cascade. Remarkably, this evolutionary novelty, which
is predicted to require a rewiring of the regulatory net-
work, was brought about by co-option of ‘ready-to
use’ pre-existing cis-regulatory elements carried by
transposing elements. Further, it was shown that
Dmrt1bY was able to bind to one of these elements,
called Izanagi, within its own promoter, leading to
significant repression of its own transcription [50]
ion
M A S C U L I N I Z A T I O NF E M I N I Z A T I O N
Estrogen
ional Regulati
Androgen/
Testo stero n e
GnRHa
Aromatase
inhibitor

D
Oryzias latipes su
ci
t
o
li
nsimorh
c
oerOoir
e
roinaDEpinephelus akaara
Fig. 1. The fish dmrt1 regulatory network or the current knowledge of dmrt1 gene regulation in fish. In many fish species, indirect dmrt1
transcriptional regulations have been described upon steroid treatment. (Upper) Steroid-induced dmrt1 regulation. Whereas feminizing sub-
stances having an estrogen-like activity (4-Nonylphenol and 17-alpha ⁄ beta estradiol) lead to dmrt1 transcriptional downregulation, masculiniz-
ing treatments (androgen, testosterone, aromatase inhibitors, estrogen antagonist or gnRHa) have been shown to conversely activate dmrt1
expression. (Lower) Proven direct regulations affecting dmrt1 transcription. In zebrafish, the transcription factor Sox5, although not itself sex-
ually dimorphically expressed, was shown to directly downregulate dmrt1 transcription during development. In addition, in medaka and tilapia
direct Dmrt1 transcriptional activity was revealed by respectively downregulating dmrt1bY and Cyp19a1a promoter activities.
A. Herpin and M. Schartl Sexual development factors in fish
FEBS Journal 278 (2011) 1010–1019 ª 2011 The Authors Journal compilation ª 2011 FEBS 1015
(Fig. 2). Interestingly, the autosomal Dmrt1a can bind
to this site. Thus the Izanagi element enables the self-
and cross-regulation of dmrt1bY expression by Dmrt1
proteins (Fig. 2). During the early stages, when the pri-
mordial gonad is determined towards testes, the exclu-
sively expressed Dmrt1bY alone exerts sex-determining
functions [9,51,52]. Noticeably, during this same period
an 11-nucleotide protein-binding motif located in the
3¢-UTR of dmrt1bY mediates gonad-specific mRNA
stability [53] (Fig. 2). This motif is conserved in the

is the primary event by which the whole gonad (germ-
line and soma) would be specified through a direc-
tional cross-talk from pre-Sertoli and Sertoli cells with
the primordial germ cells. Interestingly, at this point, a
parallel can be drawn with Dmrt1 function studies in
mice. The lack of dmrt1 in mutant mice caused a high
incidence of teratomas and resulted in a failure of
germ cells to arrest mitosis [56]. Thus, Dmrt1 in mice
and similarly Dmrt1bY in medaka appear to be regu-
lators of germ cell proliferation.
Conclusion
To conclude, it seems that the longstanding hypothesis
suggesting that the molecular sequence of sex-determi-
nation cascades might disobey the conventional rules
of evolutionary developmental is now very well sup-
ported experimentally by data gathered in fish. Indeed,
regarding Dmrt1, it is now obvious that because of
consistent expression patterns in the gonads, and
although necessarily acting at different stages of the
sex-determining cascade, these effectors must individu-
ally fulfil similar and highly conserved functions.
Hence, beyond the fish sphere, data recently published
in Xenopus and chicken (see [14, 15] this minireview
series) about dmrt genes being demonstrated to be of
first importance for gonadal determination support the
Transcriptional
regulation
Post-transcriptional
regulation
Post-translational

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