Ectopic expression of the gene elt-7 in C. elegans leads to defects in chemosensation. The author expressed elt-7, end-1, and end-3 in different tissues and developmental stages of C. elegans and measured their ability to sense and move towards a food source. Ectopic elt-7 expression most strongly impaired chemosensation, while end-3 expression caused lesser defects. Further, the more downstream a gene is in gut development, the more severe the impact on chemosensation. This suggests that mis-expression of gut developmental genes can disrupt sensory functions in C. elegans.

1. The Effect of Ectopic Expression of elt-
7 on C. elegans’ Chemosensation
By Robert A. Sumner
Mentor: Misty Riddle

2. Background
http://en.wikipedia.org/wiki/C_elegans
• C. elegans is a model organism
– Receptiveness to transgenes and RNAi
– Known cell lineage
– Known cellular anatomy

3. Endoderm cascade genes
During the
development of
the C. elegans’
endoderm, genes
are turned on in a
cascade to
promote the
specialization of
the endoderm
cells into intestinal
cells.
http://www.faculty.ucr.edu/~mmaduro/papers/Maduro%20and%20Rothman%20(2002).pdf

4. Ectopic ELT-7 activates elt-2::LacZ::GFP in
neurons, skin, and the pharynx
Pharynx
Skin Neurons

5. The elt-7- expressing C. elegans also
arrest as L1s.
They stop
developing
as if they
don’t have
any food,
even if
there is
food
around
them
http://www.wormatlas.org

6. Could their chemosensation be affected?
Agar Plate • Collect hs-end-1 or
hs-elt-7 synchronized L1
larva
• Heat shock at 33°C for
15 minutes
Food
• Transfer to middle line
• Count number of
worms on each side of
the plate after 24 hours

7. Positive Control: No food on plate
Control Experimental

8. Negative Control: Un-heat-shocked
worms
Control Experimental

9. The number of worms on each hemisphere of
the plate was then counted
The number of worms on
each hemisphere was
divided by the total
number of worms on the
plate; this number was
used to quantify the level
of attraction the C.
elegans had towards the
food on their plate

10. Ectopic ELT-7 and not END-1 leads to defects in
chemosensation
Inducing Heat Food
Factor -shock
END-1 No/Yes No
END-1 No Yes
END-1 Yes Yes
ELT-7 No/Yes No
P<0.0001
ELT-7 No Yes
ELT-7 Yes Yes
0.00 0.25 0.50 0.75 1.00
Repulsion No Preference Attraction

11. Ectopic end-3 leads to lesser defects in
chemosensation
IF HS Food
End-1 No No
End-1 Yes No
End-1 No Yes
End-1 Yes Yes
End-3 No No
P<0.0001 End-3 Yes No
End-3 No Yes
End-3 Yes Yes
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Repulsion No Preference Attraction

12. 3 Minute Heat-shock has similar effect on
chemosensation to No Heat-shock
Inducing Heat Food
Factor -shock
ELT-7 0min Yes
ELT-7 3Min Yes
ELT-7 15min Yes
0 0.5 1
Repulsion No Preference Attraction

13. No Significant Difference in Chemosensation After
Allowing L1 C. elegans to Arrest
No Arrest END-1
No Arrest ELT-7
No Arrest End-3
Arrested END-1
Arrested ELT-7
Arrested End-3
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Repulsion No Preference Attraction

14. Data suggests that the further along the gene
expressed is in gut development, the more the
worms’ chemosensation is affected.
Gene: Level of Attraction
end-1: 0.98
end-3: 0.73
elt-7: 0.54

15. Future Directions
• Testing whether the elt-7 expression in the neurons or
pharynx is damaging the worms’ chemosensation
• Seeing if a three-minute heat-shock is enough to
simply express elt-7 but not reprogram the worms’
pharyngeal cells
• Ectopically expressing elt-7 and other gut
developmental genes in different worm stages
(L2, L3, L4s, Adults) and seeing how it affects the
worms

16. Acknowledgments
• The Research Mentorship Program
• My Mentor: Misty Riddle
• Joel Rothman and the Rothman Lab
• California Institute for Regenerative
Medicine