Age-related non-tumorous lesions in SPF C57BL/6 mice with special reference to amyloidosis]

Non-tumorous pathological changes in C57BL/6 CrSlc mice, which were reared under a barrier system and died spontaneously, were examined. At 3 months intervals 125 to 209 mice were purchased at 4 weeks of age and raised for the supply of aged animals. A large portion of the mice were used for various experiments between 3 and 30 months of age, while not a small number died spontaneously and were autopsied. The major non-neoplastic lesion was amyloidosis, with incidence of 55.5% and 74.4% for the autopsied female and male, respectively. The organs involved were the liver, kidneys, spleen, adrenal glands, ileum, heart and lungs. Skin ulceration and its scar, cerebral vascular calcification, glomerulosclerosis and sepsis in both sexes, distension of the seminal vesicles in males, fibroblast growth of the adrenal glands in females were commonly found. Incidence of spontaneous neoplastic lesions was 69.7% and 55.1% for the female and male, respectively.     

Immune Response against Hamster Erythrocytes in the Low-Responder Mouse Strains

Antibody response against hamster red blood cells (H-RBC) was examined in inbred strains of C57BL/6, AKR, C3H/He, DDD and SL mice, and outbred CF1 mice. 1) There were strain differences in antibody response after a primary intravenous injection of H-RBC. DDD, SL and CF1 mice belonged to high-responder strains, while C57BL/6, AKR and C3H/He to low-responder strains. In the spleens of immunized CF1 and SL, 40 to 70 times as many plaque-forming cells (PFC) as those in C57BL/6 mice were detected. The magnitudes of the response were: CF1 ≒ SL>DDD>>C3H/He ? AKR>C57BL/6. 2) 2-mercaptoethanol resistant (MER) antibody was detected in neither low- nor high-responders after a primary intravenous antigen-injection. 3) After a secondary intravenous antigen-injection, MER antibody was detected in all the SL mice, but only in 30 to 50% of AKR and C57BL/6 mice. 4) A subcutaneous injection of H-RBC in Freund's complete adjuvant (FCA) did not elicit antibody production within 10 days. When mice pre-sensitized 7 days in advance w^Tith H-RBC in FCA were intravenously injected with H-RBC, enhanced antibody production of the primary type was observed in all the mouse strains. 5) In pre-sensitized mice, the extent of the enhancement of antibody production was the highest in low-responder C57BL/6 mice and the lowest in high-responder SL and CF1 strains. Thus, there was no strain difference in antibody titers or the numbers of PFC after the booster.     

The activity of alkaline phosphatase in the sera of DBA/2NCrj and CBA/BrA mice with calcified tongue lesions

Spontaneously occurring calcified lesions were found in the tongues of DBA/2NCrj and CBA/BrA mice. In the DBA/2NCrj strain, the frequency of the lesion was 80% (males) and 88% (females). The youngest age of a mouse with this lesion was 18 days after birth, and 3-4 lesions were found in the tongue of 6- to 8-week-old mice. In CBA/BrA mice, 20% of females and 48% of males had the lesions. No significant differences were found in the serum calcium concentrations in high and low lesion-developing strains, but the alkaline phosphatase activities in the high-developing DBA/2NCrj, DBA/LiA, and CBA/BrA strains were higher than in strains with no calcified lesions.     

Change of incidence of antinuclear antibodies in serum of NOD mouse with aging

Extractable nuclear antigens (ENA) were prepared from liver of C57BL/6J mouse and analyzed by SDS PAGE Western-immunoblotting techniques. Some protein components of the ENA, with molecular weights of 94 K, 65 K, 32 K, and 26 K, reacted with antinuclear antibodies in the sera of NOD mice. Incidence of antinuclear antibodies in the sera of NOD mice with aging were measured by ELISA method using the ENA as antigen. The antinuclear antibodies were not detected in young NOD mice (10 weeks old). However, the incidence increased with aging and reached 100% in the female NOD mice of 40 weeks. In the male NOD mice, the incidence of antinuclear antibodies was delayed and low in comparison with that in female.     

Strain differences of ether susceptibility in mice

The susceptibility to ether in the following six strains of mice was tested: C57BL/6, DBA/2, BALB/c, C3H/He, ICR and ddY. Mice of 4 weeks old were exposed to a flow of air containing various concentrations of ether for 90 min and the mortalities were assessed. The C57BL/6 strain was the most resistant and the C3H/He strain was the most sensitive to the lethal effect of ether. The susceptibilities of the closed colony mice, ICR and ddY, were intermediate between those of C57BL/6 and C3H/He mice. The DBA/2 and BALB/c strains were more sensitive than these closed colony mice and made up a sensitive group with the C3H/He strain. The LD50 values for ether in male mice of C57BL/6 and C3H/He were 6.0 and 3.1% atm, and in female mice of these strains were 6.6 and 3.2% atm, respectively. The ED50 value of ether which was accompanied by loss of righting reflex after exposure for 10 min was also higher in male C57BL/6 mice than in male C3H/He mice.     

Chromosomal locations and gonadal dependence of genes that mediate resistance to ectromelia (mousepox) virus-induced mortality.

Four genetic loci were tested for linkage with loci that control genetic resistance to lethal ectromelia virus infection in mice. Three of the loci were selected because of concordance with genotypes assigned to recombinant inbred (RI) strains of mice derived from resistant C57BL/6 and susceptible DBA/2 (BXD) mice on the basis of their responses to challenge infection. Thirty-six of 167 male (C57BL/6 x DBA/2)F1 x DBA/2 backcross (BC) mice died (22%), of which 27 (75%) were homozygous for DBA/2 alleles at Hc and H-2D. Twenty-eight percent of sham-castrated and 6% of sham-ovariectomized BC mice were susceptible to lethal mousepox, whereas 50% of gonadectomized mice were susceptible. There was no linkage evident between Hc or H-2D and loci that controlled resistance to lethal ectromelia virus infection in 44 castrated BC mice. Mortality among female mice of BXD RI strains with susceptible or intermediate male phenotypes was strongly correlated (r = 0.834) with male mortality. Gonadectomized C57BL/6 mice were as resistant as intact mice to lethal ectromelia virus infection. These results indicate that two gonad-dependent genes on chromosomes 2 and 17 and one gonad-independent gene control resistance to mousepox virus infection, that males and females share gonad-dependent genes, and that the gonad-independent gene is fully protective.     

Transgenic mouse model of cutaneous adnexal tumors

TMEM207 was first characterized as being an important molecule for the invasion activity of gastric signet-ring cell carcinoma cells. In order to unravel the pathological properties of TMEM207, we generated several transgenic mouse lines, designated C57BL/6-Tg (ITF-TMEM207), in which murine TMEM207 was ectopically expressed under a truncated (by ~200 bp) proximal promoter of the murine intestinal trefoil factor (ITF) gene (also known as Tff3). Unexpectedly, a C57BL/6-Tg (ITF-TMEM207) mouse line exhibited a high incidence of spontaneous intradermal tumors with histopathological features that resembled those of various human cutaneous adnexal tumors. These tumors were found in ~14% female and 13% of male 6- to 12-month-old mice. TMEM207 immunoreactivity was found in hair follicle bulge cells in non-tumorous skin, as well as in cutaneous adnexal tumors of the transgenic mouse. The ITF-TMEM207 construct in this line appeared to be inserted to a major satellite repeat sequence at chromosome 2, in which no definite coding molecule was found. In addition, we also observed cutaneous adnexal tumors in three other C57BL/6-Tg (ITF-TMEM207) transgenic mouse lines. We believe that the C57BL/6-Tg (ITF-TMEM207) mouse might be a useful model to understand human cutaneous adnexal tumors.KEY WORDS: Cutaneous adnexal tumor, Mouse model, TMEM207     

Histopathologic findings and establishment of novel tumor lines from spontaneous tumors in FVB/N mice

The inbred FVB mouse strain is used extensively in cancer research. Transgenic mice with an FVB/N background in which the expression of green fluorescent protein is under the control of various promoters have been used widely for the last decade. However, little is known about the incidence and characteristics of spontaneous tumors in these mice. In addition, only a few tumor lines have been established for use in this particular mouse strain. Our aim was to initiate a database of spontaneous tumors in our retired FVB/N breeders, analyze the histopathologic characteristics of these tumors, and establish novel tumor lines in vivo and in vitro. A total of 234 (40 male, 194 female) breeder mice were observed during their natural lifespans. The incidence of spontaneous tumors was 45.0% in male mice and 52.8% in female mice. All tumors in male mice were lung alveolar-bronchiolar (AB) neoplasms, except for 1 testis interstitial cell tumor. In female mice, histopathologic examination revealed 48 lung AB tumors, 27 mammary gland tumors, 13 ovarian tumors, and 14 other tumors. Several of these spontaneous tumors have been transplanted into FVB/N mice. One mammary adenocarcinoma (MCaP0008) and 1 lung AB carcinoma (LAP0297) were successfully transplanted subcutaneously and passaged serially in vivo. Subsequently, we established cell lines from both tumors, which were maintained in monolayer in vitro. Both of the grafted tumors and cell lines are tumorigenic in VEGF(P)-GFP/FVB and Tie2(P)-GFP/FVB mice. Establishment of these novel tumor lines will benefit both in vivo and in vitro studies on the pathophysiology of cancer in this relatively new but widely used mouse strain.     

Age-, gender-, and species-dependent mutagenicity in T cells of mice and rats exposed by inhalation to 1,3-butadiene

Experiments were performed: (i) to investigate potential age- and gender-dependent differences in mutagenic responses in T cells following exposures of B6C3F1 mice and F344 rats by inhalation for 2 weeks to 0 or 1250 ppm butadiene (BD), and (ii) to determine if exposures for 2 weeks to 62.5 ppm BD produce a mutagenic effect in female rats. To evaluate the effect of age on mutagenic response, mutant manifestation curves for splenic T cells of female mice exposed at 8-9 weeks of age were defined by measuring Hprt mutant frequencies (MFs) at multiple time points after BD exposure using a T cell cloning assay and comparing the resulting mutagenic potency estimate (calculated as the difference of areas under the mutant manifestation curves of treated versus control animals) to that reported for female mice exposed to BD in the same fashion beginning at 4-5 weeks of age. The shapes of the mutant T cell manifestation curves for spleens were different [e.g., the maximum BD-induced MFs in older mice (8.0+/-1.0 [S.D.]x10(-6)) and younger mice (17.8+/-6.1 x 10(-6)) were observed at 8 and 5 weeks post-exposure, respectively], but the mutagenic burden was the same for both age groups. To assess the effect of gender on mutagenic response, female and male rodents were exposed to BD at 4-5 weeks of age and Hprt MFs were measured when maximum MFs are expected to occur post-exposure. The resulting data demonstrated that the pattern for mutagenic susceptibility from high-level BD exposure is female mice>male mice>female rats>male rats. Exposures of female rats to 62.5 ppm BD caused a minor but significant mutagenic response compared with controls (n=16/group; P=0.03). These results help explain part of the differing outcomes/interpretations of data in earlier Hprt mutation studies in BD-exposed rodents.     

Mild Calorie Restriction Induces Fat Accumulation in Female C57BL/6J Mice

This study investigated the effects of mild calorie restriction (CR) (5%) on body weight, body composition, energy expenditure, feeding behavior, and locomotor activity in female C57BL/6J mice. Mice were subjected to a 5% reduction of food intake relative to baseline intake of ad libitum (AL) mice for 3 or 4 weeks. In experiment 1, body weight was monitored weekly and body composition (fat and lean mass) was determined at weeks 0, 2, and 4 by dual energy X‐ray absorptiometry. In experiment 2, body weight was measured every 3 days and body composition was determined by quantitative magnetic resonance weekly, and energy expenditure, feeding behavior, and locomotor activity were determined over 3 weeks in a metabolic chamber. At the end of both experiments, CR mice had greater fat mass (P < 0.01) and less lean mass (P < 0.01) compared with AL mice. Total energy expenditure (P < 0.05) and resting energy expenditure (P < 0.05) were significantly decreased in CR mice compared with AL mice over 3 weeks. CR mice ate significantly more food than AL mice immediately following daily food provisioning at 1600 hours (P < 0.01). These findings showed that mild CR caused increased fat mass, decreased lean mass and energy expenditure, and altered feeding behavior in female C57BL/6J mice. Locomotor activity or brown adipose tissue (BAT) thermogenic capacity did not appear to contribute to the decrease in energy expenditure. The increase in fat mass and decrease in lean mass may be a stress response to the uncertainty of food availability.     

Calorie restriction attenuates LPS-induced sickness behavior and shifts hypothalamic signaling pathways to an anti-inflammatory bias

Calorie restriction (CR) has been demonstrated to alter cytokine levels; however, its potential to modify sickness behavior (fever, anorexia, cachexia) has not. The effect of CR on sickness behavior was examined in male C57BL/6J mice fed ad libitum or restricted 25% (CR25%) or restricted 50% (CR50%) in food intake for 28 days and injected with 50 μg/kg of LPS on day 29. Changes in body temperature, locomotor activity, body weight, and food intake were determined. A separate cohort of mice were fed ad libitum or CR50% for 28 days, and hypothalamic mRNA expression of inhibitory factor κB-α (IκB-α), cyclooxygenase-2 (COX-2), prostaglandin E(2) (PGE(2)), suppressor of cytokine signaling 3 (SOCS3), IL-10, neuropeptide Y (NPY), leptin, proopiomelanocortin (POMC), and corticotrophin-releasing hormone (CRH) were determined at 0, 2, and 4 h post-LPS. CR50% mice did not develop fevers, whereas the CR25% mice displayed a fever shorter in duration but with the same peak as the controls. Both CR25% and CR50% mice showed no sign of anorexia and reduced cachexia after LPS administration. Hypothalamic mRNA expression of NPY and CRH were both increased by severalfold in CR50% animals preinjection compared with controls. The CR50% mice did not demonstrate the expected rise in hypothalamic mRNA expression of COX-2, microsomal prostaglandin E synthase-1, POMC, or CRH 2 h post-LPS, and leptin expression was decreased at this time point. Increases in SOCS3, IL-10, and IκB-α expression in CR50% animals were enhanced compared with ad libitum-fed controls at 4 h post-LPS. CR results in a suppression of sickness behavior in a dose-dependent manner, which may be due to CR attenuating proinflammatory pathways and enhancing anti-inflammatory pathways.     

Gender influences infectivity in C57BL/6 mice exposed to mouse minute virus

Two natural outbreaks of mouse minute virus (MMV) are described. Observations during management of the naturally infected colonies led to a study in which 4-wk-old C57BL/6NCr and C57BL/6Tac mice were inoculated oronasally with an immunosuppressive variant of MMV (MMVi), as were adult C57BL/6NCr lactating dams or their pups (age, 10 d). By day 28 postinoculation, 100% of the 4-wk-old male C57BL/6NCr and C57BL/6Tac mice, 56.2% of 4-wk-old C57BL/6NCr female and 62.5% of 4-wk-old C57BL/6Tac female mice, 100% of adult lactating C57BL/6NCr dams, and 100% of inoculated pups (10 d) had seroconverted. Serologically positive nursing dams did not infect their nursing pups. In contrast, when nursing pups were inoculated, 100% of their dams seroconverted by 28 d postinoculation. Only 1 of 4 facility sentinels (Tac:SW female mice) seroconverted to MMVi and none of the 4 research sentinels (Tac:SW female mice) seroconverted under a once-weekly bedding transfer program. Consequently, 4 new research Tac:SW sentinels of each gender (n = 8) were placed in known-positive cages at cage-change; 100% of the male mice but 0% of the females seroconverted by day 48. Study results suggest gender influences both infectivity and the ability to detect subclinical infections of MMVi. Other factors that may influence detection of MMV include mouse strain or stock, short shedding period, and prolonged time between cage changes. In light of the data from both the natural infections and the experimental cases, cessation of breeding likely will be beneficial when trying to eradicate this virus.     

Thymic nurse cell multicellular complexes in HY-TCR transgenic mice demonstrate their association with MHC restriction

This study examines thymic nurse cell (TNC) function during T-cell development. It has been suggested that TNCs function in the removal of nonfunctional and/or apoptotic thymocytes and do not participate in major histocompatibility complex restriction. We analyzed TNCs isolated from both normal C57BL/6 mice and C57BL/6 TgN (TCRHY) mice (HY-TCR transgenic mice). Using confocal microscopic analyses of TNCs isolated from C57BL/6 animals, we showed that 75%-78% of the enclosed thymocyte subset was viable, and 87%-90% of these cells expressed both CD4 and CD8. CD4 and CD8 also were expressed on TNC thymocytes isolated from both male and female HY-TCR transgenic mice. The transgenic female thymus was shown to have 17 times more TNCs per milligram of thymus than the transgenic male thymus. TNCs from HY-TCR transgenic females were 8-10 microm larger than transgenic male TNCs, and the female TNCs contained five times more thymocytes within intracytoplasmic vacuoles, with less than 4% apoptosis. However, more than 42% of the thymocytes within transgenic male TNCs were apoptotic. The large number and size of TNCs containing viable thymocytes in the female transgenic thymus suggest that TNC function is not limited to the removal of apoptotic thymocytes. We believe that the selective uptake of viable double-positive thymocytes by TNCs in C57BL/6 and HY-TCR transgenic female mice provides evidence that this interaction occurs during the process of major histocompatibility complex restriction.     

NO-donating aspirin inhibits intestinal carcinogenesis in Min (APC(Min/+)) mice

The chemopreventive effect of nitric oxide-releasing aspirin (NO-ASA) against gastrointestinal tumorigenesis was evaluated in Min (APC(Min/+)) mice. NO-ASA consists of a traditional ASA that bears covalently attached to it an NO-releasing moiety. Four groups (N=10) of six-week-old female C57BL/6J APC(Min/+) and the corresponding C57BL/6J(+/+) wild type mice were treated either with vehicle or NO-ASA 100 mg/kg/day intrarectally for 21 days. There were no signs of overt toxicity including gastrointestinal toxicity from NO-ASA. Vehicle treated Min mice had 24.7 +/- 3.8 tumors (mean +/- SEM) and NO-ASA treated Min mice had 10.1 +/- 1.4 tumors (59% reduction; P<0.001). Wild type mice showed no tumors. NO-ASA did not affect cell proliferation in small intestinal mucosa, determined by immunohistochemical staining for PCNA. Our findings establish the strong inhibitory effect of NO-ASA in intestinal carcinogenesis in the Min mouse and suggest that this agent merits further evaluation as a chemopreventive agent against colon cancer.     

Markers for heightened monitoring, imminent death, and euthanasia in aged inbred mice

The goal of this study was to identify objective criteria that would reliably predict spontaneous death in aged inbred mice. We evaluated male and female AKR/J mice, which die at a relatively young age due to the development of lymphoma, as well as male C57BL/6J and BALB/cByJ mice. Mice were implanted subcutaneously with an identification chip that also allowed remote measurement of body temperature. Temperatures and body weights were measured weekly until spontaneous death occurred or until euthanasia was performed for humane reasons. In AKR/J mice, hypothermia and weight loss began about 4 wk prior to death and increased gradually during that antemortem interval. In C57BL/6J and BALB/cByJ mice, these declines began earlier and were more prolonged prior to death. However, C57BL/6J and BALB/cByJ mice developed a relatively precipitous hypothermia during the 2 wk prior to death. For all 3 strains, the derived composite score of temperature × weight, expressed as a percentage of stable values for each mouse, was similarly informative. These changes in individual and composite measures can signal the need for closer observation or euthanasia of individual mice. Validated markers of clinical decline or imminent death can allow the use of endpoints that reduce terminal distress, do not significantly affect longevity or survival data, and permit timely collection of biologic samples.     

Quantitative assessment and characterization of visceral nociception and hyperalgesia in mice

Colorectal distension (CRD) is a well-characterized model of visceral nociception, which we adapted to the mouse. CRD reproducibly evoked contractions of the abdominal musculature [visceromotor response (VMR)], which was graded to stimulus intensity. The magnitude of VMR was greater in male C57BL6 and female 129S6 mice than in male 129S6 and B6.129 mice. In 129S6, C57BL6, and B6.129 mice strains, VMR was reduced dose dependently by morphine (1-10 mg/kg) and by the kappa-opioid agonist U-69593 (0.2-2 mg/kg), although U-69593 was significantly less potent in C57BL6 mice. In additional experiments, the VMR was recorded from adult male 129S6 mice before and after intracolonic administration of various irritants. Only 30% ethanol significantly enhanced responses to CRD. The colon hyperalgesia persisted for 14 days and was associated with a significant shift of the morphine dose-response function to the left. We believe this will be a useful model for study of visceral nociception and hyperalgesia, including studies of transgenic mice with mutations relevant to pain.     

A follow-up study of women in the synthetic rubber industry: study methods

BACKGROUND: Concerns about the possible toxic effects of workplace exposures in the synthetic rubber industry have centered on 1,3-butadiene (BD), styrene and dimethyldithiocarbamate (DMDTC). Our previous mortality studies of over 17,000 male synthetic rubber workers found an excess of leukemia that may be due to BD or BD plus other chemicals. Experimental studies have shown that BD produces mammary tumors in female mice and rats and ovarian tumors in female mice. AIM: This paper presents the methods of a follow-up study that evaluates the mortality experience of women employed in the North American synthetic rubber industry. METHODS: Women employed for at least 1 day at any of eight North American styrene-butadiene rubber plants were followed up from 1943 to 2002. Identifying and work history information were obtained from personnel records. Estimated quantitative exposure to BD, styrene and DMDTC, developed for our previous study of men, were used in this study. External analyses use the standardized mortality ratios (SMRs) to compare the cohort's cause-specific mortality rates to the rates of the female general population of the states or the province where the plants are located. Internal analyses use the Poisson regression and Cox proportional hazards models to examine specific cancer mortality rates in relation to BD, styrene and DMDTC exposure, by comparing an exposed cohort subgroup with the rate of unexposed cohort members.     

Spontaneous tumors in nude mice: effect of the viable yellow gene.

The incidence and type of spontaneous tumors in athymic nude (nu/nu) mice (partially inbred in CBA/H background) which were also carrying the viable yellow gene (Avy, derived from C57BL/6JAvy mice), were comparable to those observed in the phenotypically normal nu/+ and +/+ control crosses carrying the Avy gene. The Avy gene increases the incidence of spontaneous and induced tumors in most mouse strains. These results would argue against the thymus dependency of the putative immunological surveillance mechanisms.     

Identification and characterization of functional genes encoding the mouse major urinary proteins.

Mouse Ltk- cells were stably transfected with cloned genes encoding the mouse major urinary proteins (MUPs). C57BL/6J MUP genomic clones encoding MUP 2 (BL6-25 and BL6-51), MUP 3 (BL6-11 and BL6-3), and MUP 4 (BL6-42) have been identified. In C57BL/6J mice, MUP 2 and MUP 4 are known to be synthesized in male, but not female, liver, and MUP 3 is known to be synthesized in both male and female liver and mammary gland. A BALB/c genomic clone (BJ-31) was shown to encode a MUP that is slightly more basic than MUP 2 and was previously shown to be synthesized in both male and female liver of BALB/c but not C57BL/6 mice. Comigration on two-dimensional polyacrylamide gels of the MUPs encoded by the transfecting gene provides a basis for tentative identification of the tissue specificity and mode of regulation of each gene. DNA sequence analysis of the 5' flanking region indicates that the different MUP genes are highly homologous (0.20 to 2.40% divergence) within the 879 base pairs analyzed. The most prominent differences in sequence occur within an A-rich region just 5' of the TATA box. This region (from -47 to -93) contains primarily A or C(A)N nucleotides and varies from 15 to 46 nucleotides in length in the different clones.     

Sex and Genetic Factors Determine Osteoblastic Differentiation Potential of Murine Bone Marrow Stromal Cells

Sex and genetic factors determine skeletal mass, and we tested whether bone histomorphometric parameters were sexually dimorphic in femurs from 1 to 6 month old C57BL/6 mice. Trabecular bone volume declined more rapidly in female mice than in male littermates because of enhanced bone resorption. Although bone formation was not different between sexes, female mice exhibited a higher number of osteoblasts than male littermates, suggesting that osteoblasts from female mice may have a reduced ability to form bone. To determine the impact of sex on osteoblastogenesis, we investigated the potential for osteoblastic differentiation of bone marrow stromal cells from C57BL/6, Friend leukemia virus-B (FVB), C3H/HeJ and BALB/c mice of both sexes. Bone marrow stromal cells from female FVB, C57BL/6 and C3H/HeJ mice exhibited lower Alpl and Osteocalcin expression and alkaline phosphatase activity, and formed fewer mineralized nodules than cells from male littermates. Proliferative capacity was greater in cells from male than female C57BL/6, but not FVB, mice. Sorting of bone marrow stromal cells from mice expressing an α-Smooth muscle actin-green fluorescent protein transgene, revealed a higher yield of mesenchymal stem cells in cultures from male mice than in those from female littermates. Sex had a modest impact on osteoblastic differentiation of mesenchymal stem cells. To determine the influence of sex and genetic factors on osteoblast function, calvarial osteoblasts were harvested from C57BL/6, FVB, C3H/HeJ and BALB/c mice. Alpl expression and activity were lower in osteoblasts from C57BL/6 and C3H/HeJ, but not FVB or BALB/c, female mice than in cells from littermates. Sex had no effect on osteoclastogenesis of bone marrow cultures of C57BL/6 mice, but osteoblasts from female mice exhibited higher Rankl and lower Opg expression than cells from male littermates. In conclusion, osteoblastogenesis is sexually dimorphic and influenced by genetic factors.