Genetic Modification For Potential Biocontrol
Aquatic Invaders Summit
St Cloud, MNSt Cloud, MN
05-October, 2016
Chris [email protected](608) 781-6316
What is genetic control?
Genetic control is the exploitation of genetics to get the organism to control ITSELFITSELForganism to control ITSELFITSELF.(letting nature do the work for us)
3 Types of genetic control:
Y Y l l Y‐Y male release
RNA interference
CRISPR gene drives
Y-Y male release
PREMISE: Skew sex ratios so that there are only males…Then the invader cannot reproduceThen the invader cannot reproduce.
Won’t work for all invasive species…
Depends on XY sex determination anddetermination, and some other factors.
“Normal” Sex Determination
Humans have 22 pairsHumans have 22 pairs of “autosomes”…
… and 1 pair of“sex chromosomes”sex chromosomes
“X” “Y” – This person is male
“X” “X” – This person is femaleX X This person is female
Other types of Sex Determination
ZW Sex Determination• Chickens, Komodo Dragons, Giant
River Prawn, Moths and Butterflies, Others…
X0 Sex Determination• Grasshoppers, Crickets, Cockroaches,
Others…
Haplodiploid Sex Determination Haplodiploid Sex Determination• Bees, Ants, Wasps, Thrips, Others…
Temperature‐DependentSex Determination• Reptiles, Possibly others…
Y-Y Male Release to control a population:How it worksHow it works
x y
Normal male mated
xx
x
x
y
xx
xx xy
xy 50% female
50% lwith normal female: x xx xy 50% male
Super male mated
x yx
y
xy xy 100% malep
with normal female: x xy xy 100% male
Y-Y Male Release to control a population:How it’s madeHow it s made
X‐Y genetically male fish will develop into phenotypically female if exposed to estradiol during development
These X‐Y egg producers can then be mated with malesgg p
x y
Normal male mated
xx
x
y
y
xx
xy yy
xy 25% female 50% normal male
25% lwith feminized males: y xy yy 25% super male
Y-Y Male Release to control a population:ConsiderationsConsiderations
Deal Breakers: Sex must be determined genetically with X‐Y systemSex must be determined genetically with X Y system
with no environmental influence Individuals must not be able to spontaneously
reverse sexes Aquaculture methods must be possible
Deal Makers:Deal Makers: Low density target populations Short‐lived species Harvestable
Y-Y Male Release to control a population:ConsiderationsConsiderations
Other Considerations:
Drop it like its hot – Reversible
l l Must release many super males
Must continue for yearsy(dependent on species)
Releasing sex‐hormone‐treated fish Releasing sex‐hormone‐treated fish(FDA regulation)
Y-Y Male Release to control a population:ImplementationImplementation
1. Develop Y‐Y super males
2. Culture super males for release
3. Harvest target species
4. Release marked super malesp
5. Harvest target species (releasing recaptured super males)(releasing recaptured super males)
6. Repeat – Culture/Harvest/Release
RNA interference (RNAi)
PREMISE: Trick the organism into “thinking” important genes are unimportant on the cellular levelgenes are unimportant on the cellular level.
Use the organism’s own Use the organism s own molecular machinery to shut down cells.
Specific to DNA sequence beyond just species, but y j p ,targets genes of that species.
The Central Dogma of Biology
DNA ‐> RNA ‐> Protein
XX
RNA interference targets RNA molecules forRNA interference targets RNA molecules for destruction thus preventing protein from being made
RNA interference
RNAi tricks the cell into destroying its y gown mRNA
RISC – RNA Induced Silencing Complex
Small d bl d ddouble‐stranded RNA molecules guide RISC in what mRNA to slice upmRNA to slice up
We choose very specifically what genes to turn offWe provide the small dsRNA, and the target individuals do the rest
RNA interference: Delivery Mechanism
Microparticle: Filled with interfering dsRNA Filled with interfering dsRNA May require significant dose Apply as needed – degrades over time
Food source: Genetically modified plankton/etc produces interfering RNA Establish GMO population – Inoculates water body from invasionp p y Risk of escapement Potentially difficult to reverse
Currently in use by agriculture – GMO corn resistant to corn root wormNo off‐target effects are known – Still needs further study
RNA interference: Research Required
Identify genes to target (may require sequencing)
Design interfering RNAs
Confirm interfering RNAs alter gene expression (in vitro)
Confirm altered gene expression lethality (in vitro)
Develop delivery mechanism
Lab trials
Field trials
Regulatory approval – Could be FDA and EPA
CRISPR gene drives
CRISPR: Clustered Regularly Interspaced Short Palindromic Repeats – A method for editing genomes.p g g
What’s so special about CRISPR?
Compared to previous genome editing methods:
Faster Easier and Cheaper Faster, Easier, and Cheaper
• Days instead of weeks or months
• Sequence based targeting• Sequence‐based targeting
• Hundreds instead of Thousands of $$$
More reliable targeting More reliable targeting
• 95‐98% fidelity
Fewer off target affects Fewer off‐target affects
• Less chance of unintended consequences
What’s so special about CRISPR?
Originally discovered as a bacterial defense against virusesg
• Chops up viral DNA
First human trials approved this yearpp y
• Cured Retinitis Pigmentosa
• Cured Leukemia
• Aids cure on the way
• Many genetic diseases curableMany genetic diseases curable
Malaria Resistant Mosquitos in development
How CRISPR can help with invasive species
Gene Drive: A gene that is guaranteed to pass on to all offspring.p g
Can be:
Lethal alleles
Female sterility allelesy
Modified function alleles
Considerations in using CRISPR gene drives to control an invasive speciesdrives to control an invasive species
Sexual reproduction required
Requires releasing potentially many genetically modified individuals
Not reversible
Risk for escapement
Less risky with “Daisy‐chain” drive
Research required to use CRISPR gene drives to control invasivesdrives to control invasives
Statistical modeling of the problem
In depth understanding of target species genome
• Beyond just the sequence
Design strategic CRISPRs
Develop genetically modified organisms for release
• May be a continual need
Lab trials
Field trials
Regulatory approval
Ethical Considerations
Genetic modification has been around a long time
• Crops, Dogs, Race horses
Incredibly powerful tool
What we “can do” vs. what we “should do”?
Public engagement
• Interested parties
• Scientists
• Politicians
• Public at large
Chris Merkes – [email protected] – Upper Midwest Environmental Sciences CenterUSGS Upper Midwest Environmental Sciences CenterLa Crosse, Wisconsin(608) 781‐6316