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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

like, for example, Wt1, Sox-9, Bmps and Amh (see [3]
for a review) are present in all vertebrates including fish
[4] and for most of them even in protostomes.
Keywords
Dmrt1bY; Evolution; Gonad; Ovary; Sex
determination; Sex differentiation; Steroid
hormones; Teleost; Testis; transcriptional
regulation
Correspondence
A. Herpin, University of Wuerzburg,
Physiological Chemistry, Am Hubland,
D-97074 Wuerzburg, Germany
Fax: +49 931 888 4150
Tel: +49 (0)931 888 4153
E-mail:
wuerzburg.de
(Received 5 August 2010, revised 8
December 2010, accepted 25 January 2011)
doi:10.1111/j.1742-4658.2011.08030.x
A plethora of corroborative genetic studies led to the view that, across the
animal kingdom, the gene-regulatory cascades triggering sexual develop-
ment bear little resemblance to each other. As a result, the common emerg-
ing picture is that the genes at the top of the cascade are not conserved,
whereas the downstream genes have homologues in a much broader spec-
trum of species. Among these downstream effectors, a gene family involved
in sex differentiation in organisms as phylogenetically divergent as corals,
Caenorhabditis elegans, Drosophila, frogs, fish, birds and mammals is the
dmrt gene family. Despite the attention that Dmrt1 factors have received,
to date it has not been elucidated how Dmrt1s mediate their activities and
putative downstream targets have yet to be characterized. However, a

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

might rely on conserved molecules, at least at the bot-
tom of the cascade [7]. Consistently, many of the sub-
sequently characterized metazoan Dmrt homologues
were predominantly expressed in the developing
gonads. Thus, this widespread class of factors com-
monly appeared to be directly involved in sex determi-
nation. Although homology relationships of dmrt gene
family members across all the metazoans have not
been established, for vertebrates it has been shown that
the prototype member of the gene family, designated
dmrt1, is most closely related to the Drosophila dsx
and C. elegans mab-3 genes in structure and by means
of sex-determination⁄ differentiation function. Gonadal
dmrt1 expression is generally detected at higher levels
in testes than ovaries.
The deep interest in Dmrt1 in the field of sex deter-
mination in fish came with the discovery of a dmrt1
homologue on the Y chromosome of the fish medaka
(Oryzias latipes). This Y-chromosomal gene is the
product of a gene duplication of the autosomal dmrt1a
gene and was designated dmrt1bY [8] or Dmy [9]. It
was shown to be the only functional gene in the whole
Y-specific region of the sex chromosome [10]. Muta-
tions affecting this gene result in male-to-female sex
reversal [11]. In addition, dmrt1bY transgene-induced
testis development in genetic females (XX) definitively
pointed out that it is not only necessary, but also suffi-
cient for triggering male development [12]. Considering
that dmrt1bY has all the features of the master regula-
tor of testicular differentiation in medaka (see [13] for

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-

geons, most of our knowledge stems from studies on
teleost fish. Hence, this minireview mainly concentrates
on that group. A considerable number of teleost spe-
cies are hermaphrodites, switching either from first
being males (protandrous) to become female or vice
versa (protogynous). Nevertheless, the majority of tele-
osts are gonochoristic, meaning that they exist as
males and females regardless of the primary sex deter-
mination initiating process being environmental
(temperature, social) or genetic (XY or ZW).
Gonadal dimorphic dmrt1 expression
in gonochoristic species
Male-restricted expression of dmrt1 has been reported
for North African catfish Clarias gariepinus [18], rare
minnow Gobiocypris rarus [19], Nile tilapia Oreochr-
omis niloticus [20], medaka Oryzias latipes [21] and
olive flounder Paralichthys olivaceus [22]. In lake stur-
geon Acipenser fulvescens [23], zebrafish Danio rerio
[24], Atlantic cod Gadus morhua [25], pejerrey Odontes-
thes bonariensis [26], rainbow trout Oncorhynchus
mykiss [27], shovelnose sturgeon Scaphirhynchus plato-
rynchus [28] and southern catfish Silurus meridionals
[29] a strong male-biased expression appears as the
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 1011
general rule, although some dmrt1 expression could be
detected in ovaries (see Table 1). Interestingly, when
detected in the ovary, dmrt1 expression is consistently
seen in the germ cells (Gadus morhua [25] and
Danio rerio [24]), whereas much broader and less

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]

Danio rerio G Testis and ovary High in testes Spermatogonia,
spermatocytes
spermatids and
developing oocytes
PCR, ISH [24]
Epinephelus coioides pG Testis – Spermatogonia,
spermatocytes
PCR, IC,
western blot
[32]
Gadus morhua G Testis and ovary During
spermatogenesis
Germ cells
(testis and ovary)
PCR, ISH [25]
Gobiocypris rarus G Testis – n.i. PCR [19]
Halichoeres tenuispinis pG Testis – Northern blot [33]
Monopterus albus pG Testis, ovotestis
and ovary
(sex-specific
splice variants
High in testes Gonadal epithelium,
undifferentiated germ
cells (splice variants)
PCR, ISH,
Northern blot
[34]
Odontesthes bonariensis TSD Primordial gonads During testicular
differentiation
n.i. PCR [26]

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

rather than being continuously mature individuals. In
general, for males, abundant dmrt1 expression during
preparatory and prespawning and spermatogenesis
periods was seen, in contrast to a gradual decrease
thereafter during spawning ⁄ spermination. This indi-
cates that dmrt1 may have an important role
during testicular recrudescence and particularly during
spermatogenesis.
Hence, for all gonochoristic fish species investigated
to date, the dmrt1 expression pattern was always
shown to be intimately linked to male gonadogenesis
and further differentiation (Table 1).
Dmrt1 expression in protogynous and
protandrous hermaphroditic species
In hermaphrodite fish (protogynous or protandrous),
the developmental pathways leading to either testicular
or ovarian establishment have to be plastic and suscep-
tible to the sex-inversion signals considerably beyond
embryogenesis and early larval stages, whereas in
gonochoristic species the developmental decision
towards male or female is finally and irreversibly taken
long before adulthood is reached. In this context,
dmrt1 expression dynamics were consistently shown to
parallel either the development (protogynous; black
porgy Acanthopagrus schlegeli [30], gilthead seabream
Sparus auratus [31]) or regression (protandrous;
grouper Epinephlus coioides [32], wrasse Halicho-
eres tenuispinis [33], rice field eel Monopterus albus
[34]) of the testes. This confirms the abovementioned
role during testicular development and ⁄ or spermato-

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

in chicken [15, 37] and the W-linked DM-W gene in
frog [14, 38] have been shown to be the major male
and female determinants, respectively. Altogether, it
appears that when earlier in the cascade of sex deter-
mination, the role of Dmrt1 is first to be an inducer of
sex determination. Later on, when still or only
expressed at later stages after the gonad is formed and
being by implication at a more downstream position
within the cascade, its task is restricted to a mainte-
nance function essentially in Sertoli cells.
Other dmrt genes expressed in the
fish gonads
The developmental expression of dmrt1 has been well
studied in the context of gonadal induction and main-
tenance, illuminating its important function. But what
about the other dmrt genes? Table 2 summarizes the
expression pattern of these genes in fish during devel-
opment and in the gonads. Although less-extensively
studied, two main tendencies can already be deduced
from these data. First, fish dmrt family members
(Dmrt2, -3, -4, -5) exhibit conserved expression during
the earliest stages of embryonic development in various
organs, including the undifferentiated gonads. Second,
later during development, these genes usually remain
expressed in a subset of adult organs including spinal
cord, brain and gonads. Noteworthy, male-specific
gonadal expression could be observed for dmrt3 in
medaka [39] and dmrt4 in medaka [39] and olive floun-
der [40] (Table 2). By contrast, in tilapia dmrt4 expres-
sion is exclusively detected in the ovary [41]. Finally,

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

consistent in the reported effects on dmrt1 regulation
(Fig. 1). In rare minnow [19], pejerrey [26] and zebra-
fish [44], estrogen exposure resulted in cessation of
male gonad development and sex reversal. This was
always correlated with a pronounced decrease in dmrt1
mRNA levels. Of note, in the same conditions, rain-
bow trout dmrt1 expression was only slowly inhibited
[45], indicating that a reduced permissive amount of
Dmrt1 expression might not be totally incompatible
with active ovarian differentiation. In addition, in
pejerrey, a fish with strong temperature-dependant sex
determination, by combining different raising tempera-
tures with E2 treatments, Fernandino et al. [26] could
surmise that low dmrt1 and high cyp19a1a (aromatase)
expression is connected to ovarian differentiation,
whereas the opposite is true for testicular develop-
ment. Furthermore, in females, cyp19a1a expression
increased 1 and 2 weeks before the onset of dmrt1 and
the first morphological signs of ovarian differentiation
respectively, suggested that biologically active estrogen
regulates dmrt1 expression [26].
Neurohormones (GnRHa) and either androgens, aro-
matase inhibitors or estrogen receptor antagonists have
been shown to be very potent in manipulating the sexual
phenotype of fish [4] (Fig. 1). These treatments, when
applied to gonochoristic or hermaphroditic species,
always resulted in a clear morphological masculinization
process correlated with Dmrt1 upregulation (Fig. 1). Of
note, some studies also pointed out the concomitant
downregulation of cyp19a1a expression [46,47]. It then

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

[39]
dmrt3 Danio rerio Spermatogonia, spermatocytes
Developing oocytes
Embryogenesis
Olfactory placodes, neural tube
[43]
Oryzias latipes Testis Spinal cord [39]
dmrt4 Oreochromis aureus Ovary Embryogenesis, brain [41]
Oryzias latipes Testis Embryogenesis, nasal and otic placodes,
telencephalon, branchial arches
[39]
Paralichthys olivaceus Testis During somotogenesis, gills and brain [40]
dmrt5 Danio rerio Testis (weak) and ovary (weaker):
both in developing germ cells
Embryogenesis, brain [42]
Sexual development factors in fish A. Herpin and M. Schartl
1014 FEBS Journal 278 (2011) 1010–1019 ª 2011 The Authors Journal compilation ª 2011 FEBS
whether this loop aims only at activating the male path-
way, or repressing the female one, or both.
In zebrafish, the transcription factor Sox5, although
not itself sexually dimorphically expressed, was shown
to directly downregulate dmrt1 transcription during
development. This, together with a possible negative
regulation of sox5 on cyp19a1a reported in the red-
spotted grouper (Epinephelus akaara) [49] (Fig. 1),
would constitute a perfect core for the transcriptional
regulation network of dmrt1 and cyp19a1 in gonadal
development.
Expression, regulation and functions
of dmrt1a/dmrt1bY in medaka

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

Estrogen
antagonist
Clarias gariepinus
Silurius meridionalis
Silurius meridionalis Acanthopagrus
E2
17-alpha/beta Estradiol
4-Nonylphenol
(Estrogen activity)
Odontesthes bonariensisGobiocypris rarus
ect Transcripti
Oreochromis niloticus
Epinephelus coioides
Paralichthys olivaceus
Oncorhynchus mykiss
Oncorhynchus mykiss
schlegeli
Danio rerio
Dmrt1
Indireationptional Regula
Sox 5 + GATA
?
irect Transcrip
Sox 5 Dmrt1bY
Androgen
Estrogen
Cyp19a1a
(aromatase)
Cyp19a1a
?

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

3¢-UTRs of a wide range of dmrt1 orthologous genes
from flies to mammals, indicating that different sys-
tems may employ an evolutionary conserved RNA
regulatory mechanism for this gene [53].
Later during development of the juvenile fish and in
the adult testes, where both dmrt1 genes have been
shown to be expressed, it is of note that the newly gen-
erated duplicate dmrt1bY is kept back under tight tran-
scriptional regulation of the ancestral dmrt1a gene [53].
In addition to the transcriptional regulation events, it
could be shown that at any developmental stages,
Dmrt1bY protein was subject to an intensive turnover
due to rapid degradation [54].
With respect to its biochemical function, Dmrt1bY
and the other Dmrt1s also in fish appear to act as
transcription factors. This is evident from the nuclear
localization of Dmrt1 fusion proteins [54,55] and stud-
ies showing direct effects of Dmrt1 on reporter gene
expression as well as binding to a cognate motif in
electric mobility shift assays [47,50].
Finally, linking the earliest sexual dimorphic trait
to its expression dynamic, Dmrt1bY was shown to be
possibly responsible for the male-specific primordial
germ cell mitotic arrest [55] (Fig. 2). Indeed, functional
evidence showed that expression of Dmrt1bY leads to
negative regulation of male primordial germ cell prolif-
eration prior to sex determination at the sex-determi-
nation stage [55]. This suggests that in XY medaka
males, Dmrt1bY-driven primordial germ cell number
regulation, as well as determination of pre-Sertoli cells,

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

regulation
Functions
Cell cycle
progression
Fig. 2. Medaka dmrt1a ⁄ dmrt1bY regulations and functions. Grey
arrows illustrate the different levels for which active
dmrt1a ⁄ dmrt1bY regulation mechanisms could be shown. Tran-
scriptional regulation: the feedback autoregulation of dmrt1bY
promoter activity and transregulation by its paralogue Dmrt1a is a
key mechanism of dmrt1bY transcriptional tuning. Post-transcrip-
tional regulation: a highly conserved cis-regulatory motif directs dif-
ferential gonadal synexpression of dmrt1 transcripts during gonadal
development. Post-translational regulation: Dmrt1a and Dmrt1bY
have a short half-life and consequently a high turnover. Functions:
Dmrt1bY inhibition of germ cell proliferation might be part of its
known male determining function.
Sexual development factors in fish A. Herpin and M. Schartl
1016 FEBS Journal 278 (2011) 1010–1019 ª 2011 The Authors Journal compilation ª 2011 FEBS
scheme that, whatever the sex-determination system,
more comparative studies of dmrt1 are required in
order to draw the first lines of a global core regulatory
network for sex determination.
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