Autosomal telomere exchange results in the rapid amplification and
dispersion of Csf2ra genes in wild-derived mice
Camilynn I. Brannan,
Christine M. Disteche,
Linda S. Park,
Neal G. Copeland,
Nancy A. Jenkins
Mouse Cancer Genetics Program, National Cancer Institute-Frederick, Frederick, Maryland 21702, USA
Department of Pathology, University of Washington, Seattle, Washington 98195, USA
Department of Genetics, University of Washington, Seattle, Washington 98195, USA
Received: 23 May 2001 / Accepted: 7 August 2001
Abstract. Common laboratory strains such as C57BL/6J carry a
single Csf2ra gene that maps to the distal end of Chromosome
(Chr) 19. Here we report that several species of wild mice contain
multiple Csf2ra genes. Using interspecific backcross mapping and
in situ hybridization, we demonstrate that one of these species,
Mus spretus, carries four Csf2ra genes dispersed among the distal
tips of Chrs 4, 10, 13, and 19. Our data further suggest that these
additional Csf2ra genes are not generated by retrotransposition,
but rather by nonhomologous subtelomeric exchanges that could
be mediated in part by ribosomal genes located at the subtelomeric
regions of Chrs 4, 13, and 19. Although we do not know whether
these additional Csf2ra genes are functionally active, our studies
suggest that subtelomeric exchange provides a potent means for
rapid gene amplification in the mouse.
The high-affinity receptor for granulocyte macrophage colony-
stimulating factor (GM-CSF) receptor ␣ subunit (CSF2RA) maps
to the pseudoautosomal region of the human sex chromosomes
(Rappold et al. 1992). In contrast, we have previously shown that
the murine Csf2ra gene resides on the distal end of Chr 19 in
C57BL/6J mice (Disteche et al. 1992). The protein and DNA se-
quences of the human CSF2RA and mouse Csf2ra genes show
little conservation, although their protein structural domains and
function are similar (Park et al. 1992). Although it is possible that
genes located in the pseudoautosomal region might have been lost
in the mouse and that their function is performed by other related
DNA sequences, a more likely possibility is that these genes have
undergone rapid evolutionary changes, perhaps by telomere ex-
change, in both species. The finding that both the human CSF2RA
and the mouse Csf2ra genes map near the subtelomeric ends of
their respective chromosomes supports this hypothesis. In fact, the
45-kb human CSF2RA gene has been placed between 1180 and
1300 kb from the telomere (Rappold et al. 1992).
Previously, we determined the chromosomal location of the
mouse Csf2ra gene, using in situ hybridization and a [(C57BL/6J
× M. spretus)F
× M. spretus]N
interspecific backcross mapping
panel and showed that Csf2ra maps to the very distal end of Chr
19 in C57BL/6J mice (Disteche et al. 1992). In contrast, when we
used a reciprocal [(C57BL/6J × M. spretus)F
× C57BL/6J] N
mapping panel, we found that M. spretus mice carry additional
Csf2ra related genes that are not present in C57BL/6J mice and
that map to multiple mouse chromosomes. These data suggested
that M. spretus mice carry multiple unlinked Csf2ra genes. In the
present paper, we report additional recombination mapping and in
situ hybridization studies to map these loci. Furthermore, we de-
termined the genomic organization of some of these copies of
Csf2ra and examined their presence in other mouse species. Our
data suggest that the dispersion of Csf2ra in the M. spretus genome
was probably mediated by subtelomeric exchanges.
Materials and methods
Interspecific mouse backcross mapping.
Interspecific backcross prog-
eny were generated by mating (C57BL/6J × M. spretus)F
C57BL/6J males as described (Copeland and Jenkins 1991). In total, 205
mice were used to map the Csf2ra related loci (see text for details).
DNA isolation, restriction enzyme digestion, agarose gel electrophoresis,
Southern blot transfer, and hybridization were performed essentially as
described (Jenkins et al. 1982). All blots were prepared with Hybond-N
nylon membrane (Amersham). The probe, a 1182-bp PstI/XbaI fragment of
mouse cDNA, was labeled with [␣
P] dCTP by using a nick translation
labeling kit (Boehringer Mannheim); washing was done to a final strin-
gency of 0.2 × SSCP, 0.1% SDS, 65°C. A fragment of 3.4 kb was detected
in HincII-digested C57BL/6J DNA, and fragments of 19.0, 3.8, and 3.4 kb
were detected in HincII-digested M. spretus DNA. With SphI, a 2.1-kb
fragment was identified in C57BL/6J DNA, and 2.1- and 1.2-kb fragments
in M. spretus DNA. The presence or absence of the 3.8-kb HincII and
1.2-kb SphI M. spretus-specific fragments was followed in backcross mice.
A description of the probes and RFLPs for the loci linked to Csf2ra-rs1,
including Ski and Gnb1 and to Csf2ra-rs2, including Ifng, Gli,andsi, has
been reported previously [Chr 4, (Birkland et al. 1995; Goodwin et al.
1991); Chr 10 (Justice et al. 1990; Kwon et al. 1991)]. Recombination
distances were calculated by using Map Manager, version 2.6.5. Gene
order was determined by minimizing the number of recombination events
required to explain the allele distribution patterns.
Isolation of the intronic Csf2ra probe.
The intron probe for Csf2ra
was derived by PCR amplification of mouse genomic DNA (1.25 g) by
using 0.5 U of Taq polymerase (Cetus) in a 100-l reaction containing 0.8
g of each primer GM1 (5Ј-GGAGTCCCGCCCATCCTCTC-3Ј) and
GM2 (5Ј-GCATACAGGAGCGCACCGGG-3Ј), 250
glycerol, and 2 m
. Amplification conditions were: 40 cycles of 1
min at 94°C, 1 min at 55°C, and 2 min at 72°C. The 180-bp product was
subcloned into Bluescript (Stratagene) and sequenced to confirm that it
contained intronic Csf2ra genomic DNA. The isolated product was labeled
P] dCTP by using a random prime labeling kit (Stratagene) and
was used as a probe on a Southern blot; washing was done to a final
stringency of 0.2 × SSCP, 0.1% SDS, 65°C.
In situ hybridization.
In situ hybridization was done with a [
cDNA probe for the Csf2ra gene (mGMR636 and mGMR637), as de-
scribed previously (Disteche et al. 1992). Metaphase cells were prepared
from 3-day spleen cultures from male M. spretus and M. caroli mice.
Present address, C.I.B.: Department of Molecular Genetics and Microbi-
ology, University of Florida College of Medicine, Box 100266 JHMHC,
Gainesville, Florida 32610, USA.
Correspondence to: C.I. Brannan; E-mail: Brannan@mgm.ufl.edu
© Springer-Verlag New York Inc. 2001Mammalian Genome 12, 882–886 (2001).