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Fig. 2.3
Summary of ligand and receptor genes for kisspeptin systems (
kiss1
/
kiss2
) along the
vertebrate lineage.
kiss1
and
kiss2
are suggested to be duplicated before the emergence of lamprey,
probably due to the whole genome duplication of the ancestral vertebrate. It is suggested that
kiss2
and
gpr54
-
2
were lost in marsupial and placental mammals after the divergence from the mono-
treme during mammalian evolution. Some teleost species have lost
gpr54
-
1
, but no teleosts have
lost
gpr54
-
2
, suggesting the signifi cance of gpr54-2 in the regulation of teleost reproduction,
which is opposite to the case in mammals. It is also consistent with the higher level and wider
distribution of expression of
gpr54
-
2
compared to that of
gpr54
-
1
in teleost brains. The loss of
kiss1
(
blue
) or
kiss2
(
red
) is indicated by
asterisks
(fi gure as originally published in Kanda S and
Oka Y (2012) Evolutionary insights into the steroid sensitive
kiss1
and
kiss2
neurons in the verte-
brate brain. Front. Endocrin. 3: doi:
10.3389/fendo.2012.00028
)
[
6
,
7
], because these genes are located in the same locus as their paralogues, sug-
gesting that they have been duplicated at the locus level. Because the phylogeneti-
cally old vertebrate, lamprey, has both
kiss1
and
kiss2
(see Fig.
2.3
), the duplication
of the locus probably occurred in the basal vertebrate. Presumably, the 1R or 2R
whole genome duplication
2
produced the paralogous system of
kiss1
and
kiss2
. It is
speculated that these peptides shared their receptor Gpr54 in each species in the
long evolutionary history, as discussed below.
2
In the vertebrate lineage, whole genome duplication (WGD) events [
8
] are considered to have
taken place three times in teleosts (1R-3R) and twice (1R and 2R) in tetrapods [
9
].
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