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promoter activity [
88
]. Chromatin immunoprecipitation (CHIP) analysis showed
that ER
and the transcription factor SP1 form a complex in vivo to mediate this
oestrogen activation. Interestingly, while SP1 acted as a transcriptional activator, the
SP3 protein functioned as a transcriptional repressor [
88
]. This could provide a
mechanism to explain the differential regulation of
Kiss1
transcription by oestrogen
between AVPV and ARC
Kiss1
neurons. If
Kiss1
neurons in the AVPV region
expressed high levels of SP1, then
Kiss1
expression would be stimulated by oestro-
gen. Conversely, if
Kiss1
neurons in the ARC expressed high levels of SP3, then
Kiss1
expression would be repressed by oestrogen.
Other transcription factors have been shown to be expressed in ARC
Kiss1
neu-
rons in the rat, including TTF1 [
89
], YY1, EAP1 and CUX1, and these have been
shown to be recruited to the
Kiss1
promoter in HeLa cells by CHIP assays [
86
].
GT1-7 cells have been used to examine the effects of these transcription factors on
Kiss1
promoter activity. EAP1 and CUX1 isoform p110 were found to repress tran-
scription from the
Kiss1
promoter, while YY1 and TTF1 had no effect in GT1-7
cells [
86
].
α
Cell Lines Expressing Kiss1
The laboratory of Denise Belsham has generated a large number of immortalized
cell lines from hypothalamic neurons of mice [
90
] and rats [
91
]. Cells were immor-
talized by retroviral transduction of SV40 large T-antigen to primary cultures of
dissociated cells from embryonic hypothalamic tissues. Clonal cell lines were iso-
lated for further characterization by PCR to identify their expression profi le of neu-
roendocrine markers. Each cell line had a unique signature of receptor and
neuropeptide expression. Only one out of six mouse lines was reported to express
Kiss1
(mHypoE-36/1), but all six mouse lines expressed
Kiss1r
[
92
]. It is perhaps
surprising that the mHypoE-36/1 cell line expresses both
Kiss1
and
Kiss1r
since
Kiss1r
expression has not been reported in
Kiss1
neurons in vivo [
9
]. The majority
(25 out of 32) of the rat cell lines (rHypoE series) expressed
Kiss1
[
91
]. It is not
clear why the proportion of
Kiss1
expressing cell lines was higher in the rat than the
mouse; perhaps the rat
Kiss1
neurons are more mitotically active at this embryonic
stage than in the mouse and consequently more susceptible to viral transduction.
To our knowledge, these
Kiss1
expressing cell lines have not been used yet to study
the physiology of kisspeptin neurons.
Limitations of Cell Line Models
While the use of immortalized cell lines has some advantages over whole animal
studies, there are a number of limitations and caveats to this reductionist approach.
Cell lines are no longer in the context of their normal environment, lacking input
from other neurons or glial cells. They are not subjected to the normal regulatory
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