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 Previous Article | Table of Contents | Next Article 
Blood, Vol. 91 No. 8 (April 15), 1998:
pp. 2737-2744
Bone Marrow Failure in the Fanconi Anemia Group C Mouse Model
After DNA Damage
By
Madeleine Carreau,
Olga I. Gan,
Lili Liu,
Monica Doedens,
Colin McKerlie,
John E. Dick, and
Manuel Buchwald
From the Department of Genetics, Research Institute, Hospital for
Sick Children, Toronto, Ontario, Canada; Research Services and
Pathology, Sunnybrook Health Science Centre, University of Toronto,
North York, Ontario, Canada; and the Department of Molecular and
Medical Genetics, University of Toronto, Toronto, Ontario, Canada.
 |
ABSTRACT |
Fanconi anemia (FA) is a pleiotropic inherited disease that causes
bone marrow failure in children. However, the specific involvement of
FA genes in hematopoiesis and their relation to bone marrow (BM)
failure is still unclear. The increased sensitivity of FA cells to DNA
cross-linking agents such as mitomycin C (MMC) and diepoxybutane (DEB),
including the induction of chromosomal aberrations and delay in the G2
phase of the cell cycle, have suggested a role for the FA genes in DNA
repair, cell cycle regulation, and apoptosis. We previously reported
the cloning of the FA group C gene (FAC) and the generation of
a Fac mouse model. Surprisingly, the Fac  / mice
did not show any of the hematologic defects found in FA patients. To
better understand the relationship of FA gene functions to BM failure,
we have analyzed the in vivo effect of an FA-specific DNA damaging
agent in Fac / mice. The mice were found to be highly
sensitive to DNA cross-linking agents; acute exposure to MMC produced a
marked BM hypoplasia and degeneration of proliferative tissues and
caused death within a few days of treatment. However, sequential,
nonlethal doses of MMC caused a progressive decrease in all peripheral
blood parameters of Fac / mice. This treatment targeted
specifically the BM compartment, with no effect on other proliferative
tissues. The progressive pancytopenia resulted from a reduction in the
number of early and committed hematopoietic progenitors. These results
indicate that the FA genes are involved in the physiologic response of hematopoietic progenitor cells to DNA damage.
| |
INTRODUCTION |
FANCONI ANEMIA (FA) is a recessive
inherited bone marrow (BM) failure syndrome affecting children and is
characterized by progressive aplastic anemia and a variety of
congenital malformations (reviewed in Young and
Alter1). The hematologic abnormalities are detected at a
median age of 7 years, with thrombocytopenia generally preceding the
onset of anemia. Pancytopenia was found to be associated with a
decrease in BM cellularity. FA patients are also at a higher risk of
cancer, in particular acute myeloid leukemia (AML).
At least 8 complementation groups have been identified, designated FA-A
through FA-H,2 that may correspond to specific gene defects
involving either the same biochemical pathway or alternative biological
functions. Although two genes have been cloned (groups A and C), the
basic cellular defect(s) in FA is not known.3-5 It has been
postulated that the FA genes may be implicated in DNA repair due to the
increased sensitivity of FA cells to DNA cross-linking agents, such as
mitomycin C (MMC) and diepoxybutane (DEB), which induce chromosomal
aberrations and abnormal delay in the G2 phase of the cell cycle.
Studies on different cell lines have suggested abnormalities in other
cellular processes, such as oxygen metabolism, growth factor
homeostasis, cell cycle regulation, differentiation, and
apoptosis.6-8 No specific function has been attributed to
either of the two cloned genes. The most studied gene, FAC,
encodes for a protein that is highly hydrophobic and localized to the
cytoplasm,9 which precludes, for now, any direct role in
DNA repair. No homologies have been found to known genes, proteins, or
domains that could serve as clues to its biological role. In addition,
comparison between human, mouse, rat, and bovine FAC sequences
did not show any clearly delineated functional domains.10
To study the relationship of FA genes to BM failure, two mouse models
of FA complementation group C have been generated by disruption of the
mouse Fac gene.11,12 Although spleen cells obtained
from mutant mice showed sensitivity to DNA cross-linking agents,
Fac / mice did not exhibit any changes in blood
parameters or in the amounts of hematopoietic progenitors, consistent
with the hematologic phenotype seen in FA patients. The only phenotype observed was compromised gametogenesis similar to that seen in FA
patients,1 although this phenotype is also observed in
other mutant mice for genes involved in DNA repair.13-15 To
further understand the physiological function of the FAC gene
and its relation to the clinical phenotype seen in patients, we have
exposed the Fac / mice to a specific DNA-damaging
agent. Treatment of Fac / mice with low doses of
MMC results in depletion of the early and committed hematopoietic
progenitors leading to progressive pancytopenia.
| |
MATERIALS AND METHODS |
Mice and MMC injections.
Five- to 6-month-old Fac mice11 from different
genetic backgrounds, consisting of 50% 129/R1 contribution associated
with either 50% Balb/c, C57BL/6J, or 129/ag, were injected
intraperitoneally with varying doses of MMC (Boehringer Mannheim,
Canada, Laval, Quebec, Canada) diluted in saline solution. Control mice
received saline injections of equivalent volumes. MMC-treated mice
received either one single injection ranging from 0.01 to 1 mg/kg or
weekly injections of 0.3 mg/kg. Mice body weight ranged from 25 to 40 g. The animal experiments were approved by the Animal Care Committee of
the Hospital for Sick Children.
Histopathological analysis.
Mice were euthanized and tissues were immediately collected and placed
in 10% neutral-buffered formalin. Fixed tissues were embedded in
paraffin, sectioned at 4 µm, and stained with hematoxilin-eosin using
standard methods.
Hematologic analysis.
Complete peripheral blood counts, including erythrocytes, leukocytes,
and platelets, were obtained with an automated counting apparatus.
Heparinized blood was collected in an eppendorf tube from the mouse
tail tip. To determine leukocyte and platelet counts, peripheral blood
was depleted of red blood cells by treatment using Zapisoton solution
from Coulter Electronics (Miami, FL), as described by the
manufacturer. For hematopoietic committed progenitor cell assays
(colony-forming cells [CFC]), BM and spleen cells were collected
either from femurs or spleen, seeded in complete methylcellulose medium
according to the manufacturer (Stem Cell Technology, Vancouver, British
Columbia, Canada), and incubated for 7 to 10 days at 37°C, 5%
CO2. To determine the number of granulocytes (G),
macrophages (M), or GM colonies, BM cells were plated at 2 to 2.5 × 104 cells/mL and spleen cells at 1 to 4 × 105 cells/mL. For the determination of erythroid (E)
colonies (burst-forming unit-erythroid [BFU-E]) or mixed
GME-megakaryocyte colonies, BM cells were plated at 1 × 105 cells/mL and spleen cells at 4 to 8 × 105 cells/mL. The total number of colonies was counted and
depicted here as CFC. For in vitro sensitivity to MMC, various
concentrations of MMC, ranging from 2 to 10 nmol/L, were added to the
methylcellulose cultures at plating. BM cells from Fac
/ mice were plated at increasing concentrations with
increasing MMC doses to obtain countable numbers of colonies. For
long-term BM cultures (LTBMC), BM cells collected from femurs were
plated as previously described,16 with some minor
modifications.17 Cells were cultured at 33°C for 5 weeks. One half of media was replaced weekly, and at the end of the
culture period, nonadherent fraction and adherent layer cells (ALC)
were tested for their capacity to initiate colony formation (CFC).
Nonadherent cells were seeded in methylcellulose at 2 to 10 × 105 cells/mL. ALCs were harvested by trypsinization,
depleted of stromal cells by attachment to plastic culture dishes for
20 minutes at 37°C, and seeded in methylcellulose at 4 to 8 × 104 cell/dish for 7 to 10 days. All cultures were performed
in triplicates. CFC numbers are expressed as the total number of CFC
from the nonadherent and adherent fractions.
Statistical analysis.
Results are expressed in mean ± SEM. Estimation of the significance
of the difference between means was performed using the Student's
paired t-test.
| |
RESULTS |
Low-dose MMC induced pancytopenia in Fac / mice.
To test the in vivo sensitivity of Fac / mice to
the cross-linking agent MMC, we first measured the effect of various
doses of drug, ranging from 0.03 to 1 mg/kg, on hematopoiesis.
Fac / mice showed hypersensitivity to single
doses of 1 mg/kg, which induced death within 10 days
(Fig 1A). Before death, peripheral white
blood cell counts were reduced by 90%, hematocrit by 50%, and body
weight by 30% in Fac / injected mice (data not
shown). The estimated LD50 for Fac /
mice was between 0.5 and 0.6 mg/kg, 10 times lower than for wild-type
mice (data not shown). No effect was observed on either Fac +/+
or Fac +/ mice (Fig 1A). To better reflect more
physiologic challenges that human patients may encounter in the
environment, we exposed the Fac / mice to
sequential, nonlethal doses of MMC. We found that repeated injections
of 0.3 mg/kg of MMC caused death in the Fac /
mice within 3 to 8 weeks, although a single injection had no lethal
effect (Fig 1B). Weekly injections of 0.3 mg/kg MMC caused a
progressive decrease in all peripheral blood parameters, with a marked
decrease in platelet counts (Fig 2). Mice
used in these experiments died between 6 and 8 weeks of treatments.
Death followed shortly after a 50% decrease in red blood cell counts.
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| Fig 1.
Hypersensitivity of Fac / mice to MMC. (A)
Survival curves of Fac +/+, +/, and / mice from
different genetic backgrounds after one injection of 1 mg/kg MMC. (B)
Survival curves of Fac +/+ and / mice from different
genetic backgrounds after weekly injections of 0.3 mg/kg MMC. Controls
include Fac / mice that received weekly saline injections
or one single injection of 0.3 mg/kg MMC. Survival is expressed as the
percentage of the number of live mice subjected to MMC treatment (n = 17). All control animals survived for up to several months before being
killed for histological analysis.
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| Fig 2.
Peripheral blood parameters of Fac / and
Fac +/+ mice. (A) Red blood cells (RBC), (B) white blood
cells (WBC), and (C) platelets. Measurements were made in mice from a
50%/50% 129ag/129R1 background treated with repeated MMC injections
(0.3 mg/kg). Results are expressed as the mean number of cells measured
in 4 mice. Mice used in this experiment died between 6 and 8 weeks of
treatment. All control mice survived for more than 12 weeks before
being killed for histological analysis. Fac / mice that
received a single MMC injection or Fac +/ mice gave
similar results as control Fac +/+ mice. Each point
represents the mean ± SEM of four separate determinations. The
absence of SEM bars represents values too low to appear in the graph.
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MMC is highly toxic to proliferative tissues of Fac
/ mice.
Histological analysis of Fac / BM tissue sections
showed that a single MMC dose of 0.3 mg/kg caused a slight reduction in BM cellularity (Fig 3B), although repeated
injections or chronic exposure to MMC (once per week for 5 weeks)
markedly depleted all BM cell populations of Fac
/ mice (Fig 3D). Cellularity was estimated to be less
than 10% and megakaryocytes were completely absent in Fac
/ sections examined, which correlate with the initial
progressive decrease observed in platelet counts. BM sections from
Fac +/+ (Fig 3A and C) and Fac +/ (data not
shown) mice that received single or repeated injections of 0.3 mg/kg of
MMC showed no remarkable effects. Repeated exposure to 0.3 mg/kg of MMC
had no significant effect on other tissues of all MMC-injected mice. Moderate atrophy of the gastric glandular mucosa was
observed in some tissue sections from Fac / mice,
although this was not significant enough to contribute to the death of
the animals.
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| Fig 3.
Histological appearance of tissues from mice after
chronic exposure to MMC. Hematoxylin-eosin stained sections of BM
(×400) from mice (50%/50% C57Bl/6/129R1 genetic background) after
chronic exposure to MMC; 1 (A and B) or 5 (C and D) weekly injections of 0.3 mg/kg MMC. (A and C) Fac +/+; (B and D) Fac
/.
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In contrast, analysis of tissue sections from Fac
/ mice after acute exposure to MMC (one single
injection of 1 mg/kg) showed that death resulted from massive damage to
highly proliferative tissues, including BM, gastric lining, and mucosa
of the small and large intestine (Fig 4B,
D, and F). The BM sections from Fac / mice showed
a marked reduction in cellularity, with depletion of all cell types and
almost complete absence of megakaryocytes (Fig 4B). This dramatic
reduction in BM cellularity after acute exposure to MMC resembled
chronic long-term exposure to low doses of MMC. No changes in BM
cellularity were observed in either Fac +/+ (Fig 4A) and
Fac +/ injected mice (data not shown). In
other proliferative tissues, the gastric and intestinal lining of
Fac / mice injected with high doses of MMC showed
marked degeneration and flattening of epithelial cells associated with
edema and mononuclear inflammatory cell infiltration in the subjacent
lamina propria (Fig 4D and F). Hepatocellular swelling and degeneration
and splenic lympholysis was also observed in Fac
/ mice (data not shown). However, at high doses of
MMC, no effect was observed on the stomach, intestine, or any other
tissues of Fac +/+ (Fig 4C and E) and Fac +/
mice (data not shown). No apparent damage was detected in the brain,
heart, lung, or kidney of any MMC-injected mice (data not shown).
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| Fig 4.
Histological appearance of tissues from mice after acute
exposure to MMC. Hematoxylin-eosin stained sections of mouse tissues (50%/50% C57Bl/6/129R1 genetic background) after acute exposure to
1.0 mg/kg MMC. (A and B) BM (×400); (C and D) glandular stomach (×200); (E and F) large intestine (×200). (A, C, and E) Fac
+/+; (B, D, and F) Fac /.
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MMC treatment reduces both clonogenic and primitive hematopoietic
progenitors.
To determine if MMC was acting on early subsets of hematopoietic
cells, we measured the number of early and committed progenitors present in Fac +/+, +/, and /
mice after in vivo exposure to either acute or chronic MMC treatment
(Fig 5). For acute exposure, the number of
BM progenitors was determined 2 and 6 days after a single MMC injection
of 0.75 mg/kg. Fac / mice had a 90% to 95%
reduction in the number of CFC at days 2 and 6, as compared with
saline-injected Fac / mice (Fig 5A). A slight
increase in CFC, although not significant (15% and 30% at days 2 and
6, respectively), was observed in Fac +/+ injected mice. BM
from Fac +/ mice showed a significantly lower level of
CFC at day 2 (27% of Fac +/+ control) but showed normal levels
at day 6 (data not shown). Similar results were obtained from spleen
CFC from Fac / mice, which had a decrease in
progenitor contents at both time points (data not shown). The number of
committed progenitors was also measured in mice after chronic MMC
treatment. CFC from both BM and spleen were evaluated at 1, 3, or 5 weeks after weekly exposure to low doses of MMC (0.3 mg/kg; Fig 5B and
C). BM CFC levels from low-dose injected Fac /
mice decreased to 16% after the first week and to less than 1% after
3 weeks. CFC in spleen were markedly reduced to less than 3% after the
first week of treatment and to less than 1% after 3 weeks. Chronic
exposure to MMC showed a stimulatory effect on the number of committed progenitors from Fac +/+ mice, in which a twofold increase in CFC levels was observed in both BM and spleen after 5 and 3 weeks, respectively. This response is typical of the overshoot in progenitors seen in mice treated with other chemotherapeutic
agents.18,19
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| Fig 5.
In vivo MMC sensitivity of CFC from BM and spleen cells
of Fac +/+ and Fac / mice. (A) The number of
CFC established 2 and 6 days after a single MMC injection (0.75 mg/kg).
(B and C) The number of CFC in BM (B) and spleen (C) after 1, 3, and 5 weekly injections of MMC (0.3 mg/kg). Controls represent
saline-injected mice. Data represent the mean ± SEM of triplicate
determinations from 2 mice. Significant differences between controls
and MMC-injected mice (*P < .01; **P < .05;
#P < .005; ##P < .0005). The absence of SEM bars
represents values too low to appear in the graph.
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We also measured the in vitro sensitivity of BM clonogenic progenitors
to increasing concentrations of MMC (Fig
6). Clonogenic cells from Fac / mice were highly
sensitive to MMC treatment, showing a dose-dependent decrease in colony
formation. This indicates a direct action of MMC on committed
hematopoietic progenitor cells.
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| Fig 6.
In vitro MMC sensitivity of BM CFC cells from Fac
/, +/, and +/+ mice. BM cells were seeded in the
presence of increasing concentration of MMC and cultured for 7 to 8 days. Curves represent the percentage of CFC relative to untreated
cells. Each point represents the mean ± SEM of two separate
experiments each performed in triplicate.
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To measure the effect of MMC on more primitive hematopoietic cells or
long-term culture-initiating cells (LTC-IC), we established 5-week BM
cultures (LTBMC) of BM cells from acute and chronic MMC-exposed mice
(Fig 7). Five-week LTBMC enables the
detection of cells capable of producing CFC for at least 5 weeks and is a reliable indicator of primitive cells.23,24 Acute
exposure to MMC reduced the number of Fac /
LTC-IC cells by more than 90% in cultures from both time points (Fig
7A). LTC-IC from Fac+/+ showed a fivefold increase in CFC at
day 2, which returned to control levels at day 6. We also estimated
LTC-IC after repeated exposure to low doses of MMC (Fig 7B). The number
of LTC-IC in both Fac/ and Fac +/+ LTBMC
cultures decreased to 33% of control level after one MMC injection.
Growth was completely abolished in Fac / LTBMC
initiated after 3 weekly injections of MMC. The total number of cells
from these cultures were plated, but no CFC were observed. Fac
+/+ mice showed a progressive increase in LTC-IC from LTBMC after 3 and
5 weekly injections of MMC. Similar levels of CFC formation to
Fac +/+ were found in Fac +/ LTC-IC cells (data
not shown). These results are in agreement with the histological
studies and demonstrate that death after repeated exposure to MMC is
caused by progressive loss of early (LTC-IC) and committed progenitors
causing BM failure.
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| Fig 7.
In vivo MMC sensitivity of BM LTC-IC cells from
Fac +/+ and Fac / mice. (A) The number of CFC
from 5-week LTBMC established 2 and 6 days after 1 single MMC (0.75 mg/kg) injection. (B) The number of CFC from 5-week LTBMC established
1, 3, and 5 weeks after repeated MMC injection of 0.3 mg/kg. Controls
represent saline-injected mice. Data represent the mean ± SEM of
triplicate determinations from 2 mice. Significant differences between
controls and MMC-injected mice (*P < .01; **P < .05; #P < .005; ##P < .0005). The absence of SEM
bars represents values too low to appear in the graph.
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DISCUSSION |
We, and others, have generated mouse models for Fanconi anemia to
better understand the pathophysiology of this BM failure syndrome.11,12 Although Fac / mice
have no FAC protein present in their cells, these animals do not
naturally develop any of the hematologic phenotypes characteristic of
the disease. Absence of a hematologic phenotype in Fac
/ mice may be attributed to the lack of a stressful
insult and/or response to DNA damage in the target tissue (BM).
Because mouse models generated by the disruption of DNA repair genes
only manifest phenotypes similar to those of the human disease after
the induction of disease-specific DNA damage,20-22 we
analyzed the in vivo effect of an FA-specific DNA-damaging agent, MMC.
Under these conditions, Fac / mice developed a
phenotype remarkably similar to that seen in FA patients.
Fac / mice were found to be highly sensitive to
DNA cross-links and showed a marked decrease in survival to MMC doses
10 times lower than in normal mice. Acute exposure to MMC not only produced a marked BM hypoplasia in Fac / mice but
also degeneration of the liver, spleen, and small and large intestines,
resulting in death within a few days after treatment. These results
correlate with the increased toxicity found in FA patients after
exposure to the cross-linking agent cyclophosphamide used in
conditioning regimens before BM transplantation.23-25
The increased sensitivity of Fac / mice to MMC is
similar to the one observed in MGMT-deficient mice after
N-methyl-N-nitrosourea treatment or in ATM-deficient
mice after  -irradiation and correlates with toxicity of unrepaired
disease-specific DNA lesions in proliferative tissues.13,15,26 However, chronic MMC treatment or
progressive accumulation of lower levels of DNA lesions seemed to
specifically target the hematopoietic system of Fac
/ mice, affecting early (LTC-IC) and committed (CFC)
progenitors, suggesting that FAC specifically regulates regeneration of
hematopoietic progenitors after DNA damage. These results also imply
that other proliferative tissues such as gastrointestinal tissue can
either tolerate a certain level of damage or rapidly regenerate
progenitors, whereas the BM compartment cannot. These observations also
support the notion that Fac / mice lack stressful
insults in clean animal facilities.
In vivo exposure of Fac / mice to low doses of
MMC induced a dramatic pancytopenia, the result of BM failure.
Fac / mice died shortly after a
decrease in all peripheral blood cells. This phenotype resembles that
observed in FA patients in that thrombocytopenia or pancytopenia is
often associated with decreased BM cellularity and is the first
indicator of BM failure. In MMC-treated Fac / mice, BM failure was associated with decreased BM cellularity and, more
specifically, by a reduction in the number of committed (CFC) and more
primitive (LTC-IC) progenitor cells. Loss of in vitro growth potential
of progenitors is also observed in FA patients and was found to
correlate with poor clinical status.27 Also, the increased
in vitro MMC sensitivity observed in CFC from Fac / mice is remarkably similar to that seen in FA patients.
These results suggest that primitive hematopoietic FA cells are highly sensitive to DNA cross-linking agents and that their loss results in BM
failure. Although FA patients are not in close contact to MMC, other
agents present in the environment that can mimic cross-linking activity
may induce DNA lesions in their BM cells, contributing to BM failure.
Injury to other BM components, such as the surrounding stroma,
and/or disregulation of growth factor homeostasis may also influence the decrease and regeneration of hematopoietic cells after
damage. FA patients were shown to have abnormal levels of tumor
necrosis factor  (TNF) and interleukin-6 in their serum fractions, which may, at high levels, be toxic to the BM cell populations.28-30 We did not observe any increase in TNF
levels in Fac / mice after chronic exposure to
MMC or other stimuli such as lipopolysaccharides (data not shown),
suggesting that changes in growth factor levels may occur locally or be
a secondary effect to immune responses from infections to which these
Fac / mice have not been subjected.
MGMT / and ATM / mice have an increased
sensitivity to bacterial infection after DNA damage, supporting the
notion that impairment of the BM cell compartment in FA patients may
contribute to an increased risk of infection triggering immune
responses and thus high TNF levels.13,15,26 This again
supports the view that mice in animal colonies lack natural exposure to
stressful agents from the environment that would contribute to the
phenotype.
MMC is a well-known DNA cross-linking agent that may generate, although
to a lesser extent, DNA damage through oxygen radical formation. Thus,
damage to the BM compartment may also result from abnormal oxygen
metabolism and increased production of reactive oxygen species
(ROS).31 In vitro and ex vivo studies of FA cells have
demonstrated overproduction of ROS and increased sensitivity to oxygen,
as well as an increase in ROS-induced DNA lesions, particularly
8-hydroxy-2 -deoxyguanosine.37-39 However, this may be a secondary feature to the basic defect, because FA-C cells transfected with the FAC gene failed to complement their
oxygen-induced growth inhibition.32 Regardless of whether
abnormal oxygen metabolism is the fundamental defect in FA, direct or
indirect excess production of oxidative DNA damage may contribute to
the decrease in hematopoietic progenitors leading to BM failure in FA
patients as in Fac / mice.
FA patients were found to have an increased risk of cancer,
particularly acute myelogenous leukemia (AML), but we did
not observe any tumor formation in untreated or MMC-treated
Fac / mice. However, because mice
subjected to acute or chronic MMC treatments died either from toxicity
after acute treatment or BM failure after chronic treatment, tumor
formation in these mice could only have been detected if they had
survived the treatment.
Differences in types or abundance of species-specific genes may
influence the FAC-mediated pathway and interfere or compensate for its
absence. In preliminary experiments, we have observed differences in
survival after chronic MMC treatment in Fac / mice from different strains, suggesting the involvement of modifier genes in the development of the FA-specific phenotype. Because the
genetic background is known to modify the expression of mutant phenotypes,33 variation in the severity of the hematologic
phenotype may be observed in different inbred strains of Fac
/ mice.
FA is considered a DNA repair related disease and a chromosomal
instability syndrome due to the high cellular sensitivity to DNA
cross-linking agents and occurrence of spontaneous or induced chromosomal breakage. The specific function of FAC has yet to be
defined, but studies on in vitro systems and its cytoplasmic localization have suggested a role in either cell cycle regulation or
apoptosis rather than in DNA repair.7,9 Also, studies on
cross-link removal in FA cells have also demonstrated contradictory results as to a defect in DNA repair.34-36 Studies on mice
deficient for nucleotide excision repair genes have shown that
phenotypes corresponding to the human disease occur only after DNA
damage induction,20-22 whereas mice defective for a
putative signal transduction protein, ATM, show spontaneous phenotypes
even in the absence of DNA damage.13,15 Furthermore,
inactivation of antiapoptotic genes, such as Bcl-2 or
Bcl-x, leads to short-lived animals or a lethal
phenotype.37,38 In comparison to those data, our in vivo
studies would indicate that FAC has a more direct role in DNA
repair than in either signal transduction or apoptosis. To reconcile
previous findings with our in vivo results, FAC may act as a sensor of
DNA damage and function as an inducer of repair; thus, lack of repair
affects both cell cycle progression and possibly induces apoptosis.
Experiments are under way to determine if apoptosis contributes to the
decrease in Fac / BM progenitors after DNA damage.
The development of a Fac mouse model with a hematologic
phenotype similar to that seen in FA patients should be useful for further studies of the genesis of BM failure and to test novel therapies for FA. This Fac mouse model should also help
characterize the role of FA genes in the response to DNA damage and
their relationship to BM function.
| |
FOOTNOTES |
Submitted August 7, 1997;
accepted November 23, 1997.
Supported by grants from the National Cancer Institute of Canada with
funds from the Canadian Cancer Society (J.E.D. and M.B.), the Fanconi
Anemia Research Fund (Eugene, OR; M.B.), the Bayer Canadian Red Cross
Society Research and Development Fund (M.B.), the Medical Research
Council of Canada (J.E.D.), the Canadian Genetic Diseases Network of
the National Centers of Excellence (J.E.D.), a Research Scientist award
from the NCIC and an MRC scientist award (J.E.D.), and the Sunnybrook
Trust for Medical Research (C.M.).
Address reprint requests to Madeleine Carreau, PhD, Department of
Genetics, Research Institute, Hospital for Sick Children, 555 University Ave, Toronto, Ontario, Canada M5G 1X8.
The publication costs of this article were defrayed in part by page
charge payment. This article must therefore be hereby marked
"advertisement" in accordance with 18 U.S.C. section 1734 solely to indicate this fact.
| |
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Abstract
Introduction
Abstract