Biology Reference
In-Depth Information
JH is a lipid like hormone that functions together with 20E to regulate
developmental timing and possibly adult processes as well. JH primarily
functions like an anti-metamorphic hormone: presence of JH ensures that
the periodic pulses of 20E produce another immature larvae. When the
larvae have attained a critical size in the last larval stage, loss of JH coupled
with a rise in JH metabolism, leads to 20E mediated metamorphosis (for
review
Jindra et al., 2013
). Other processes affected by JH include behavior,
reproduction, diapause, stress resistance, and aging (
Flatt, Tu, & Tatar,
2005
). Unlike 20E, much less is known regarding the mechanism of JH
signaling as the receptors involved in JH mediated signaling have until
recently eluded identification (
Jindra et al., 2013
).
4.2. Identification of Ecdysone- and JH-regulated miRNAs
20E and JH promote developmental transitions by activating pathways
that lead to global changes in gene expression, including the expression of
particular miRNAs as indicated by developmental profiling of miRNAs.
These include
miR-100
,
let-7
,and
miR-125,
whose expression is upregulated
at the larval-to-pupal transition, as well as
miR-8
and
miR-34
, whose expres-
sion is downregulated during the larval-to-pupal transition (
Aravin et al.,
2003; Jin, Kim, & Hyun, 2012; Leaman et al., 2005; Sempere, Sokol,
Dubrovsky, Berger, & Ambros, 2003
). Treatment of cultured
Drosophila
cells
with purified 20E triggers the expression of
miR-100
,
let-7
,and
miR-125
and
represses the expression of
miR-8
and
miR-34
along with an additional
miRNA,
miR-14
(
Bashirullah et al., 2003; Garbuzov & Tatar, 2010; Jin
et al., 2012; Sempere, Dubrovsky, Dubrovskaya, Berger, & Ambros, 2002;
Sempere et al., 2003; Varghese & Cohen, 2007
). While
miR-34
is repressed
by 20E treatment, it is activated by the JH analog, methoprene, though this
increase in
miR-34
expression is completely suppressed by simultaneous
treatment of S2 cells with 20E. Moreover,
miR-34
expression increases in
mutant larvae containing mutations in either
Ecdysoneless
(
ecd
), a gene required
for Ecdysone biosynthesis, or the 20E primary response gene
broad
(
Sempere
et al., 2003
). Thus, 20E and JH pathways appear to have opposite effects on
expression of
miR-34
, and interplay of these two signaling pathways may be
required for the temporal downregulation of
miR-34
during metamorphosis
and its subsequent upregulation in adult flies. Taken together, this data
indicates that endocrine signaling pathways activate one class of miRNAs
and repress another, and that these miRNAs may play important roles in
promoting progression through developmental transitions.
