Biology Reference
In-Depth Information
as higher temperature can induce female to male reversion (however, see
also Frisch et al., 2007).
DMY
and its paralogue
Dmrt1
bY gene, found only in
O. latipes
and
O. curvinotus
, is a duplicated copy of the autosomal region, which spans to
258Kb and contains only one functional
DMY
gene. This Y specifi c region
has originated from a transposition of the duplicated autosomal region
(Matsuda et al., 2002; Nanda et al., 2002). A single amino acid change from
Thr
in the three sequences to
Ser
in the four
Dmrt1
sequences has been
largely responsible for the establishment of
DMY/Dmrt1bY
as male sex
determination gene (Zhang, 2004). This Y chromosome specifi c
DM
domain
gene is required for male development.
The strain Hd-rR
HNI
of
O. latipes
,
a hybrid strain generated using a
strain carrying sex determining region
HNI
and Hd-rR strain carrying the
R dominant red body color gene on the Y chromosome and its allele the r
for the recessive white body color (Shinomiya et al., 1999). Matsuda et al.
(2007) sub-cloned the
DMY
HNI
genomic region of
O. latipes
to the
p
CC1 vector
from BAC. The vector containing
DMY
HNI
genomic fragment was injected
into one-cell stage embryos of medaka d-rR strain. Expectedly, 57 orange-
red adult male (XY) and 58 white (XX) adult females were obtained in the
F
1
generation. Genomic PCR-RFLP analysis revealed that both transgenic
and non-transgenic individuals, which carried the sex determining region
with
DMY
HNI
differentiated into males. However, due to overexpression
of
DMY,
some of the transgenics, that carried the sex determing region
namely
DMY
HNI
became either fertile or sterile females (Fig. 7). Of the 58
white XX fi sh, 13 (22%) displayed secondary sex characteristics of male.
Further overexpression of
DMY
cDNA also caused XX sex reversal to male,
as indicated by the presence of acinus in some and delayed developing
ovaries with reduced number germ cells or with incomplete follicles
in others. These fi ndings demonstrate that
DMY
is suffi cient for male
development in medaka and suggest that the functional difference between
the X and Y chromosome is a single gene. Incidentally, YY female medaka
with mutant-type of
DMY
genes on their Y chromosomes are completely
fertile, indicating that the X and Y chromosomes are functionally the same
except for the male determining function (Otake et al., 2008).
2.3 Sex differentiation genes
In an attempt to survey the genes that are involved in sex differentiation
in fi sh, relevant information is compiled from the reviews of von Holfsten
and Olsson (2005), Pala et al. (2009), Sandra and Norma (2009) and Siegfried
(2010).
