MicroRNAs act sequentially and asymmetrically to control chemosensory laterality in the nematode

1
MicroRNAs act sequentially and asymmetrically to
control chemosensory laterality in the nematode

• Sarah Chang, Robert J. Johnston JR, Christian
  Frokjaer-Jensen, Shawn Lockery and Oliver Hobert

2
MicroRNAs

• Small RNAs that regulate expression of
  complementary messenger RNA
• Found in diverse groups of animals, and many of
  these microRNAs are phylogenetically conserved
• Animal microRNAs prevent the expression of
  specific messenger RNAs by binding to their 3
  untranslated region.

3
The bilaterally symmetrical chemosensory neurons
ASE left (ASEL) and ASE right (ASER) display
left/right asymmetrical gene expression patterns

• Guanylyl cyclase receptor genes gcy-6 and gcy-7
  are only expressed in ASEL, whereas gcy-5 is only
  expressed in ASER
• The chemosensory capacities of these two neurons
  is also asymmetrical.

4
The microRNA lsy-6 is required for the left/right
asymmetrical expression of the (gcy) genes in
ASEL and ASER, but the regulatory pathway is
poorly understood

• An essential component of ASEL/R laterality is
  the restriction of lsy-6 expression to the ASEL
  neuron
• Conducted genetic screens for mutants that show
  defects in asymmetric expression of ASE specific
  chemoreceptors.
• Ot26 showed 100 lsy phenotype both ASE cells
  expressed the normally ASER specific gcy-5 gene,
  and concomitantly lost the expression of the
  normally ASEL specific gcy-7

5
(No Transcript)
6
Ot26 is an allelle of the die-1 gene

• The die-1 gene encodes a C2H2 zinc-finger
  transcription factor
• die-1 expression is present in both ASEL and
  ASER, but expression is strongly biased towards
  ASEL

7
Die-1 expression is strongly biased towards ASEL
8
(No Transcript)
9
Die-1 (ot26) mutant animals exhibit a complete
loss of lim-6 homeobox gene expression

• Correct lim-6 expression requires a regulated
  balance of the ceh-36 activator homeobox gene and
  the cog-1 repressor gene.
• Loss of lim-6 could either mean an increase in
  expression of the ceh-36 activator or a decrease
  in expression of the cog-1 repressor.
• loss of die-1 had no effect on ceh-36 expression

10
Die-1acts through lsy-6 to repress cog-1
expression
11
How is die-1 and hence lsy-6 activation spatially
biased towards ASEL

• Previously shown that cog-1 expression is
  controlled by the miRNA lsy-6 binding to the
  cog-1 3 UTR.
• Is die-1 expression also controlled by its 3
  UTR.
• constructed sensor genes, in which gfp
  constructs were produced under the control of the
  ceh-36 promoter in both ASEL and ASER

12
(No Transcript)
13
Mir-273 a microRNA controls die-1 by binding to
its 3UTR

• die-1 3UTR contains sequences that are
  complementary to mir-273
• Expression of mir-273 is significantly higher in
  ASER than in ASEL
• Forced symmetric expression of mir-273 represses
  die-1 expression, and hence disrupts ASE
  laterality. Transgenic animals that express
  mir-273 from the bilateral ceh-36 promoter
  exhibit downregulation of the die-1rescgfp
  expression and also show the 2-ASER chemoreceptor
  profile characteristic of the die-1 mutant
  phenotype.

14
Bilateral expression of mir-273 disrupts die-1
expression
15

• The asymmetric expression of gcy-7 and gcy-5 is
  specified by differential expression of upstream
  transcription factors including die-1, cog-1, and
  lim-6.
• Die-1 is translationally repressed in ASER by the
  mir-273 miRNA, and cog-1 is translationally
  repressed in ASEL by lsy-6 miRNA.

16
(No Transcript)