Chromosome Counts for ES Cells - Testing for Euploid Clones
1. Why count chromosomes in gene
targeted ES cells?
It is recognized that not all cell lines in culture have normal
chromosome complements. Numerous groups have observed that aneuploid ES
cell clones do not form germline ES cell-mouse chimeras (exception:
germline transmission from X:O ES cells can occur through female
chimeras). We routinely detect aneuploid ES cell clones in our
experiments, in gene trap clones imported from international consortia,
and in clones generated independently by other laboratories. Deriving
and breeding ES cell chimeras from aneuploid ES cells is expensive with
respect to animals used, time, and money. The simple chromosome
counting method below can improve the efficiency of germline
transmission in any experiment. We count 20 spreads per ES clone in our
Transgenic Core Facility. We microinject ES cell clones in which 60% or
more of the spreads contain 40 chromosomes. Note that simply because
most of the chromosome spreads in an ES cell clone are euploid is no
guarantee that the clone will go germline.
2. Why not karyotype
chromosomes in gene targeted ES cells?
A karyotype shows and identifies each chromosome in a spread.
This identification of the chromosomes in multiple spreads is a time
consuming process. Commercial services for karyotyping are
available, but can add dramatically to the cost of a gene targeting
project. Although some ES cell lines with 40 chromosomes will be
aneuploid because of chromosome duplications and deletions, the
proportion of ES cell clones with euploid chromosome counts that go
germline is so high that there is no real advantage to screening the
cells by karyotype analysis.
Download Chromosome Counting Protocol
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