Project: Research project


A number of aging theories predict that there is a relationship
between somatic mutations and aging processes, but few systems
exist to test this hypothesis at a specific locus. This proposal
describes the construction of a model system which will
ultimately allow for: 1) a quantitative assessment of the
frequency of somatic mutations as a function of age, 2) a
determination of the mechanisms of somatic cell mu-action in
vivo, and 3) a qualitative assessment of changes in the types of
mutations in somatic cells during growth and development. To
accomplish this, a cohort of mice will be constructed with a
heterozygous deficiency at a defined locus and a primary cloning
assay will be used to identify and analyze those cells which have
undergone a mutation leading to the homozygous deficient state. The construction of mice with a specific heterozygous deficiency
requires a mutation at a selectable locus and a means to introduce
this mutation into a mouse population. The autosomal purine
salvage locus adenine phosphoribosyltransferase (APRT) is chosen
for this study because: it is selectable and dispensable in
mammalian cells and a DNA probe for the mouse gene is
available. To construct mice with a heterozygous deficiency at
the APRT locus, the mouse embryonal stem cell system will be
used. These cultured stem cells are capable of differentiating
into numerous cell types under the appropriate stimulus. Most
dramatically, they can be injected into a developing mouse
blastocyst and will participate in formation of a variety of organs.
The resultant mouse, termed a chimera, is therefore partially
derived from a cell type which was maintained in vitro. By
selecting for an embryonal cell with a homozygous deficiency for
APRT, it will be possible to construct a chimeric mouse with this
deficiency. Further, by breeding functional germ line chimeras
with wild-type mice, it will be possible to obtain F1 progeny with
heterozygous deficiencies for APRT. These mice will then be
used for long-term studies to determine if the frequency and
spectrum of somatic cell mutations at a specific autosomal locus
are altered as a function of age.
Effective start/end date7/1/886/30/93


  • National Institutes of Health
  • National Institutes of Health
  • National Institutes of Health
  • National Institutes of Health
  • National Institutes of Health


Stem Cells
Adenine Phosphoribosyltransferase
DNA Probes
Growth and Development
Germ Cells
Cultured Cells


  • Medicine(all)