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| Chemical mutagenesis is a powerful tool for functional
annotation of the mouse genome sequence. A collaborative three-generation
screen for recessive ENU-induced neurological and behavioral mutations
is underway. In addition, individual scientists run smaller scale sensitized
or targeted screens for mutations affecting pathways of neurodegeneration,
prion disease, hearing, ear and kidney development, or peripheral myelination.
Mutations that are not relevant to our own research programs are available
to outside investigators. Our past experience in posting dominant mutations
for adoption on our web site was disappointing, so we decided not to
post probable mutations from a subsequent three-generation screen for
recessive mutations in C57BL/6J mice. However, we continued to notify
individuals with known interests in particular phenotypes. The cost
and cage space required to confirm that recurrent phenotypes within
a pedigree were heritable were significant factors in the decision to
discard the majority of probable mutations. However, we recently adopted
a more efficient breeding scheme for our recessive mutation screen.
This new screen may allow us to use genetics to confirm and provide
preliminary map locations for most recurring phenotypes within a pedigree.
We hope that posting results of our screen will lead to new collaborations
and wider use of potentially valuable mutations. |
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| The recessive screen at McLaughlin Research Institute
starts with ENU-treated C57BL/6J male mice that are mated with C3H.SW-H2b/SnJ
to produce the G1 pedigree founders. Each C3B6F1 founder is mated
with C3H.SW to produce G2 daughters for mating back to the their
G1 father.
Generally, four G2 daughters produce four families of G3 mice for
screening. This strategy is illustrated in the Figure below. |
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| Screening on an outbred background offers some advantages
over screening inbred mice (there also are disadvantages). In addition
to improved breeding performance and larger litter sizes, the mixed
genetic background selects for robust phenotypes. More subtle probable
mutations (those with identical phenotypes that occurred several times
within a pedigree) that were identified in our inbred screen often disappeared
when outcrossed for mapping. The current cross to produce G3 for screening
also is a mapping cross; since, on average, 62.5% of the genome is C3H-derived,
a preliminary map location can be obtained with relatively few affected
mice. Genotyping results thus are helpful in refining the phenotyping
assays. Finally, since cryopreserved F1 sperm is more readily recoverable
than sperm from inbred mice, every mutation that is detected can be
archived. A pilot project is currently underway with the goal of posting
every mutation, along with preliminary mapping data and a list of candidate
genes if appropriate. Mutant mice will be available at no charge other
than shipping for two to three weeks after posting. If mutant mice are
discontinued as live stock, frozen sperm from the pedigree founder will
be available for recovery either in the requestor’s own lab or
by our transgenic facility on a fee basis. |
| Contact George
Carlson if you would like to be notified when particular phenotypes
appear or if you have a simple test that we might be able to incorporate
into our screen. |
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