A locus for radiation-induced gastroschisis on mouse Chromosome 7
Institut fu¨r Medizinische Strahlenbiologie, Universita¨tsklinikum Essen, Hufelandstr.55, 45122 Essen, Germany
Unite de Genetique des Mammiferes, Institut Pasteur, 25 rue du Docteur-Roux, 75724 Paris cedex 15, France
Institut fu¨r Sa¨ugetiergenetik, GSF-Forschungszentrum fu¨r Umwelt und Gesundheit, Ingolsta¨dter Landstr.1, 85764 Neuherberg, Germany
Received: 13 May 1998 / Accepted: 6 August 1998
Abstract. Gastroschisis (abdominal wall defects) occurs with a
high frequency in the mouse inbred strain HLG compared with
C57BL/6J mice. The risk of gastroschisis increases significantly
after exposure to irradiation with X-rays during preimplantation
development and follows a recessive mode of inheritance for the
HLG susceptibility alleles. We have used a backcross strategy and
genome-wide microsatellite typing to chromosomally map this
trait. A suggestive linkage for a locus responsible for radiation-
induced gastroschisis (Rigs1) was found in a region of mouse
Gastroschisis, a herniation of the abdominal viscera, occurs in
humans with a frequency of one in 8000 (Eurenius and Axelsson
1994) and is also frequently observed in mice (Werler et al. 1992).
The reasons for gastroschisis are not known. Some explanations
based on embryologic studies do exist: (1) somatopleure differen-
tiation deficiency in embryonic mesenchyme (Duhamel 1963), (2)
in utero thrombosis of the omphalomesenteric artery (Hoyme et al.
1983), (3) premature obliteration of the right umbilical vein
(Moore and Stokes 1953). Each abnormality would result in a
paraumbilical or umbilical ring disruption and intestinal eviscera-
In the HLG (Heiligenberger) inbred mouse strain, gastroschisis
occurs spontaneously with a frequency of about 3%. Furthermore,
this strain shows an increased risk of gastroschisis after irradiation
of the embryos in the 1-cell stage. Studies performed with the HLG
mice have demonstrated that radiation exposure (0.25–2.0 Gy X-
rays or 0.125–1.0 Gy neutrons) of mouse zygotes significantly
increases the number of malformed fetuses (mainly gastroschisis),
with a dose-effect relationship (Pampfer and Streffer 1988).
In line with the results obtained with zygotes, a statistically
significant increase in the number of gastroschisis was also ob-
served when oocytes were exposed to X-rays within 1–4 weeks
before ovulation (Mu¨ller and Schotten 1995). Irradiation of germ
cells during various stages of spermatogenesis similarly induced
gastroschisis in the HLG strain, and the proportion of fetuses with
this malformation increased with the radiation dose in a dose-
dependent manner (Mu¨ller et al. 1994).
In contrast to the HLG mouse strain, C57BL/6J mice do not
respond to radiation exposure of zygotes with an increase in mal-
formations. In crosses between HLG and C57BL/6J mice, the sen-
sitivity of gastroschisis after irradiation of zygotes is slightly but
not significantly increased, compared with the frequency observed
in the C57BL/6J mice (Mu¨ller et al. 1995). This suggests a reces-
sive mode of inheritance for the HLG susceptibility allele(s). The
frequency of gastroschisis after backcrossing is consistent with the
control by two or three loci of the susceptibility to radiation-
induced gastroschisis (Hillebrandt et al. 1996). In the present
study, a linkage analysis for these loci was carried out in offspring
derived from a cross between (C57BL/6J × HLG)F
HLG males. Genome-wide microsatellite typing for markers in the
group of mice with gastroschisis and deviation from the expected
1:1 ratio of parental alleles was made. Our results indicate that at
least one of the loci responsible for the development of radiation-
induced gastroschisis maps to mouse Chromosome (Chr) 7 close to
the marker D7Mit195.
Materials and methods
The mouse strain under study was established as an
inbred strain of NMRI-like mice in Freiburg (Germany) in 1939 and was
colony-bred from 1975 onwards at the Institute of Medical Radiobiology in
Essen. In the meantime, this strain has been registered after more than 20
generations of inbreeding as the ‘‘HLG/Zte’’ strain. The experiments de-
scribed in this paper have been carried out with the inbred mice.
A cross between HLG and C57BL/6J-mice not showing malformations
was performed (Mu¨ller and Schotten 1995). (C57BL/6J × HLG)F
females were back-crossed with HLG males.
Radiation exposure of the zygotes and collection of fetuses.
HLG-male and three sexually mature C57BL/6J- or (C57BL/6J × HLG)F
females were mated from 7 a.m. to 9 a.m. Females with a vaginal plug
indicating copulation were either X-irradiated with 1 Gy or 1.7 Gy or
sham-irradiated at 12 a.m. of the same day (3 h post conception). At this
time zygotes have completed the second meiotic division and already con-
tain two haploid pronuclei (Streffer et al. 1980; Weißenborn and Streffer
1988). The X-ray source used was a Stabilipan machine (Siemens, Erlan-
gen, Germany) operating at 240 kVp and 15 mA with a 0.5-mm Cu filter.
The dose rate was 1 Gy/min.
On gestation day 19, pregnant mice were killed by cervical dislocation
and the fetuses were examined for malformations. Irradiated fetuses with
gastroschisis as well as a subset of normal fetuses were collected.
Livers were isolated from individual fetuses, and DNA was prepared by
a standard procedure. Genotyping was performed with microsatellite
primer pairs obtained from Research Genetics (Huntsville, Ala., USA) and
under PCR conditions as recommended by the manufacturer.
Linkage analysis was performed with Gene-Link, a
program for backcross genetic linkage analysis that is able to detect link-
age, transmission ratio distortion, epistatic interactions, and test for two to
three locus models in simple or multigenic traits (Montagutelli 1990,
1996). The p-value of the departure from the expected 1:1 ratio was cal-
culated with the binomial distribution. 2×2 contingency tables were ana-
lyzed by Fisher’s exact test.
Teratogenic events in the backcross. The frequencies of gastros-
chisis in the HLG, C57BL/6J mice and in the (C57BL/6J × HLG)
Correspondence to: S. Hillebrandt, email@example.com
© Springer-Verlag New York Inc. 1998Mammalian Genome 9, 995–997 (1998).