Cutting edge: Autoimmune disease in day 3 thymectomized mice is actively controlled by endogenous disease-specific regulatory T cells

Female B6AF1 mice thymectomized on day 3 (d3tx) develop autoimmune ovarian disease (AOD) and dacryoadenitis. It has been hypothesized that d3tx breaks tolerance by depleting late ontogeny regulatory T cells (Treg). We now report that Treg greatly expand over effector T cells in d3tx mice and adoptively suppress autoimmune disease in d3tx recipients. In the d3tx donors, Treg from ovarian lymph nodes (LN) preferentially suppress AOD and Treg from lacrimal gland LN preferentially suppress dacryoadenitis, suggesting they are strategically positioned for disease control. Indeed, the autologous disease in d3tx mice is dramatically enhanced by in vivo depletion of endogenous Treg. Moreover, normal 3-day-old mice possess Treg that suppress AOD and autoimmune gastritis as efficiently as adult cells. Thus, d3tx mice possess disease-relevant Treg of presumed neonatal origin. They accumulate in the regional LN and actively inhibit concurrent autoimmune disease; however, they cannot fully prevent autoimmune disease development.     

Endogenous oocyte antigens are required for rapid induction and progression of autoimmune ovarian disease following day-3 thymectomy

Female (C57BL/6xA/J)F(1) mice undergoing thymectomy on day 3 after birth (d3tx) developed autoimmune ovarian disease (AOD) and autoimmune disease of the lacrimal gland. As both were prevented by normal adult CD25(+) T cells, regulatory T cell depletion is responsible for d3tx diseases. AOD began as oophoritis at 3 wk. By 4 wk, AOD progressed to ovarian atrophy with autoantibody response against multiple oocyte Ag of early ontogeny. The requirement for immunogenic endogenous ovarian Ag was investigated in d3tx female mice, d3tx male mice, and d3tx neonatally ovariectomized (OX) females. At 8 wk, all mice had comparable lacrimalitis but only those with endogenous ovaries developed AOD in ovarian grafts. The duration of Ag exposure required to initiate AOD was evaluated in d3tx mice OX at 2, 3, or 4 wk and engrafted with an ovary at 4, 5, or 6 wk, respectively. The mice OX at 2 wk did not have oophoritis whereas approximately 80% of mice OX at 3 or 4 wk had maximal AOD, thus Ag stimulus for 2.5 wk following d3tx is sufficient. AOD progression requires additional endogenous Ag stimulation from the ovarian graft. In mice OX at 3 wk, ovaries engrafted at 5 wk had more severe oophoritis than ovaries engrafted at 6 or 12 wk; moreover, only mice engrafted at 5 wk developed ovarian atrophy and oocyte autoantibodies. Similar results were obtained in mice OX at 4 wk. Thus endogenous tissue Ag are critical in autoimmune disease induction and progression that occur spontaneously upon regulatory T cell depletion.     

H2 control of natural T regulatory cell frequency in the lymph node correlates with susceptibility to day 3 thymectomy-induced autoimmune disease

Day 3 thymectomy (D3Tx) results in a loss of peripheral tolerance mediated by natural regulatory T cells (nTregs) and development of autoimmune ovarian dysgenesis (AOD) and autoimmune dacryoadenitis (ADA) in A/J and (C57BL/6J × A/J) F(1) hybrids (B6A), but not in C57BL/6J (B6) mice. Previously, using quantitative trait locus (QTL) linkage analysis, we showed that D3Tx-AOD is controlled by five unlinked QTL (Aod1-Aod5) and H2. In this study, using D3Tx B6-Chr(A/J)/NaJ chromosome (Chr) substitution strains, we confirm that QTL on Chr16 (Aod1a/Aod1b), Chr3 (Aod2), Chr1 (Aod3), Chr2 (Aod4), Chr7 (Aod5), and Chr17 (H2) control D3Tx-AOD susceptibility. In addition, we also present data mapping QTL controlling D3Tx-ADA to Chr17 (Ada1/H2), Chr1 (Ada2), and Chr3 (Ada3). Importantly, B6-ChrX(A/J) mice were as resistant to D3Tx-AOD and D3Tx-ADA as B6 mice, thereby excluding Foxp3 as a susceptibility gene in these models. Moreover, we report quantitative differences in the frequency of nTregs in the lymph nodes (LNs), but not spleen or thymus, of AOD/ADA-resistant B6 and AOD/ADA-susceptible A/J, B6A, and B6-Chr17(A/J) mice. Similar results correlating with experimental allergic encephalomyelitis and orchitis susceptibility were seen with B10.S and SJL/J mice. Using H2-congenic mice, we show that the observed difference in frequency of LN nTregs is controlled by Ada1/H2. These data support the existence of an LN-specific, H2-controlled mechanism regulating the prevalence of nTregs in autoimmune disease susceptibility.     

Maternal autoantibody triggers de novo T cell-mediated neonatal autoimmune disease

Although human maternal autoantibodies may transfer transient manifestation of autoimmune disease to their progeny, some neonatal autoimmune diseases can progress, leading to the loss of tissue structure and function. In this study we document that murine maternal autoantibody transmitted to progeny can trigger de novo neonatal pathogenic autoreactive T cell response and T cell-mediated organ-specific autoimmune disease. Autoantibody to a zona pellucida 3 (ZP3) epitope was found to induce autoimmune ovarian disease (AOD) and premature ovarian failure in neonatal, but not adult, mice. Neonatal AOD did not occur in T cell-deficient pups, and the ovarian pathology was transferable by CD4(+) T cells from diseased donors. Interestingly, neonatal AOD occurred only in pups exposed to ZP3 autoantibody from neonatal days 1-5, but not from day 7 or day 9. The disease susceptibility neonatal time window was not related to a propensity of neonatal ovaries to autoimmune inflammation, and it was not affected by infusion of functional adult CD4(+)CD25(+) T cells. However, resistance to neonatal AOD in 9-day-old mice was abrogated by CD4(+)CD25(+) T cell depletion. Finally, neonatal AOD was blocked by Ab to IgG-FcR, and interestingly, the disease was not elicited by autoantibody to a second, independent native ZP3 B cell epitope. Therefore, a new mechanism of neonatal autoimmunity is presented in which epitope-specific autoantibody stimulates de novo autoimmune pathogenic CD4(+) T cell response.     

Impact of intra- and interstrain cross-fostering on mouse maternal care

The importance of maternal care in shaping an individual's phenotype in health and disease is becoming more and more apparent in both human and animal studies. However, in mouse studies using inbred strains or knockout mice to analyze the genetic influences on the development of normal and aberrant behavioral phenotypes, maternal behavior is very poorly characterized and often ignored. This study provides an extensive analysis of spontaneous maternal behavior of inbred mice in three conditions: (1) comparing two commonly used strains, (2) analyzing the impact of adopting pups from the same strain (intrastrain cross-fostering) and (3) analyzing the impact of adopting pups from a different strain (interstrain cross-fostering). For each condition, maternal behavior was analyzed continuously over 23-h periods on postnatal days 2, 4, 6 and 9. We report that (1) the maternal behavior of C57BL/6J and DBA/2J dams toward their biological offspring is highly similar, (2) intrastrain cross-fostering has minimal impact on maternal behavior of C57BL/6J and DBA/2J dams, (3) interstrain cross-fostering does not modify the strain differences in maternal care observed between AKR and C3H/He mothers and (4) the pup strain does influence the amount of maternal behavior shown by both mothers in interstrain cross-fostering. These latter findings demonstrate that both mother strain and pup strain are key determinants of maternal behavior.     

Interacting quantitative trait loci control loss of peripheral tolerance and susceptibility to autoimmune ovarian dysgenesis after day 3 thymectomy in mice

Day 3 thymectomy (D3Tx) results in a loss of peripheral tolerance mediated by CD4(+)CD25(+) T cells and the development of autoimmune ovarian dysgenesis (AOD) in A/J and (C57BL/6J x A/J)F(1) (B6AF(1)) hybrids but not in C57BL/6J mice. Quantitative trait loci (QTL) linkage analysis using a B6AF(1) x C57BL/6J backcross population verified Aod1 and Aod2 that were previously mapped as qualitative traits. Additionally, three new QTL intervals, Aod3, Aod4, and Aod5, on chromosomes 1, 2, and 7, respectively, influencing specific subphenotypes of AOD were identified. QTL linkage analysis using the A x B and B x A recombinant inbred lines verified Aod3 and confirmed linkage to H2. Aod5 colocalized with Mater, an ovarian-specific autoantigen recognized by anti-ovarian autoantibodies in the sera of D3Tx mice. Sequence analysis of Mater identified allelic, strain-specific splice variants between A/J and C57BL/6J mice making it an attractive candidate gene for Aod5. Interaction analysis revealed significant epistatic effects between Aod1-5 and Gasa2, a locus associated with susceptibility to D3Tx-induced autoimmune gastritis, as well as with H2. These results indicate that the QTL controlling D3Tx-induced autoimmune phenomenon are both organ specific and more generalized in their effects with respect to the genesis and activity of the immunoregulatory mechanisms maintaining peripheral tolerance.     

CD40 ligand in pathogenesis of autoimmune ovarian disease of day 3-thymectomized mice: implication for CD40 ligand antibody therapy

The blockade of CD40 ligand (CD40L) is effective in autoimmune disease prevention. Recently, a brief period of CD40L mAb treatment was reported to induce tolerance and enhancement of CD4(+)CD25(+) regulatory T cell activity. We therefore determined the efficacy of CD40L mAb treatment in autoimmunity that resulted from CD4(+)CD25(+) regulatory T cell deficiency. Autoimmune ovarian disease (AOD) and oocyte autoantibody response of day 3-thymectomized (d3tx) mice were inhibited by continuous CD40L mAb treatment from day 3, or from days 10-14, whereas CD40L mAb treatment confined to the neonatal week was ineffective. The enhanced expression of memory markers (CD44 and CD62L(low)) on CD4(+) T cells of the d3tx mice was unaffected by CD40L mAb treatment. In contrast, their increased T cell activation markers (CD69 and CD25) were eliminated by CD40L mAb treatment. Moreover, ex vivo activated T cells of d3tx mice expressed elevated intracellular IFN-gamma, and this was also blocked by CD40L mAb. The memory T cells, although nonpathogenic in CD40L mAb-positive environment, transferred severe AOD to CD40L mAb(-) neonatal recipients. Most importantly, CD40L mAb treatment inhibited AOD in recipients of T cells from d3tx donors with severe AOD and led to regression of AOD in d3tx mice documented at 4 wk. Therefore, 1) the continuous presence of CD40L mAb both prevents and causes regression of AOD in the d3tx mice; and 2) the multiple steps of the d3tx autoimmune disease, including T cell activation, cytokine production, T cell-mediated inflammation, and tissue injury, are CD40L dependent.     

Effects of prolactin deficiency during the early postnatal period on the development of maternal behavior in female rats: Mother's milk makes the difference

During early life, prolactin (PRL) ingested by the pups through the milk participates in the development of neuroendocrine, immunological and reproductive systems. The present study tested whether a deficiency in PRL in the dam's milk during early lactation affected the offspring in terms of the maternal responsiveness in the sensitization paradigm and behavioral response to a novel environment in the offspring. Thus, lactating rats were injected (sc) on postnatal days (PND) 2–5 with bromocriptine (125 μg/day), bromocriptine + ovine PRL (125 μg + 300 μg/day), or vehicle. As juveniles (at PND 24) or adults (PND 90–100), one female from each litter was exposed to 5 foster pups continuously for 8 days and their maternal responsiveness was recorded. Female offspring were also tested in an open field arena. Adult, but not juvenile, female offspring of bromocriptine-treated mothers showed an increased latency to become maternal, in comparison to latencies displayed by the offspring of control mothers. Furthermore, the proportion of adult, but not juvenile, offspring of bromocriptine-treated mothers that became maternal was lower than that showed by the offspring of vehicle-treated mothers. In comparison to female offspring of vehicle-treated mothers, female offspring of bromocriptine-treated mothers spent less time hovering over the pups (as juvenile females), body licking (as both juvenile and adult females), and in close proximity to pups (as adult females) during the maternal behavior test. Simultaneous administration of ovine PRL and bromocriptine reversed almost all the negative effects of bromocriptine. These data suggest that maternally-derived PRL participates during the early postnatal period in the development of neural systems that underlie the control of maternal behavior.     

Zinc metabolism in lethal-milk mice. Otolith, lactation, and aging effects

Lethal-milk (lm), a recessive mutation, occurred in the C57BL/6J inbred strain of mice. Lactating lm dams produce a zinc-deficient milk that is lethal to all nursing pups. If foster-nursed on normal dams, lm pups survive and become reproductively mature. Injection of zinc-glycinate into the pups or zinc supplementation of the water of the lactating dams reduces lethality. Other pleiotropic effects in lm mice include congenital otolith defects with delayed righting, "tail-spinning," and abnormal swimming. These effects are diagnostic criteria for segregation of lm mice among backcross progeny. About 40 percent of the expected number of lm pups survive to weaning. Zinc supplementation of the dam improves development of saccular but not of utricular otoliths; zinc does not improve survival of the lm pups among backcross progenies. The lm mice over eight months of age also exhibit extensive hair loss, dermatitis, and skin lesions. Possible roles of metallothionein in zinc and copper metabolism are discussed in regard to the pleiotropic effects of the lethal-milk mutation.     

Elimination of maternally transmitted autoantibodies prevents diabetes in nonobese diabetic mice

The influence of maternally transmitted immunoglobulins on the development of autoimmune diabetes mellitus in genetically susceptible human progeny remains unknown. Given the presence of islet beta cell-reactive autoantibodies in prediabetic nonobese diabetic (NOD) mice, we abrogated the maternal transmission of such antibodies in order to assess their influence on the susceptibility of progeny to diabetes. First, we used B cell-deficient NOD mothers to eliminate the transmission of maternal immunoglobulins. In a complementary approach, we used immunoglobulin transgenic NOD mothers to exclude autoreactive specificities from the maternal B-cell repertoire. Finally, we implanted NOD embryos in pseudopregnant mothers of a non-autoimmune strain. The NOD progeny in all three groups were protected from spontaneous diabetes. These findings demonstrate that the maternal transmission of antibodies is a critical environmental parameter influencing the ontogeny of T cell-mediated destruction of islet beta cells in NOD mice. It will be important to definitively determine whether the transmission of maternal autoantibodies in humans affects diabetes progression in susceptible offspring.     

Involvement of the GHSR in the developmental programming and metabolic disturbances induced by maternal undernutrition

The mismatch between maternal undernutrition and adequate nutrition after birth increases the risk of developing metabolic diseases. We aimed to investigate whether the hyperghrelinemia during maternal undernourishment rewires the hypothalamic development of the offspring and contributes to the conversion to an obese phenotype when fed a high-fat diet (HFD). Pregnant C57BL/6 J, wild type (WT) and ghrelin receptor (GHSR)^−/− mice were assigned to either a normal nourished (NN) group, or an undernutrition (UN) (30% food restricted) group. All pups were fostered by NN Swiss mice. After weaning, pups were fed a normal diet, followed by a HFD from week 9. Plasma ghrelin levels peaked at postnatal day 15 (P15) in both C57BL/6 J UN and NN pups. Hypothalamic Ghsr mRNA expression was upregulated at P15 in UN pups compared to NN pups and inhibited agouti-related peptide (AgRP) projections. Adequate lactation increased body weight of UN WT but not of GHSR^−/− pups compared to NN littermates. After weaning with a HFD, body weight and food intake was higher in WT UN pups but lower in GHSR^−/− UN pups than in NN controls. The GHSR prevented a decrease in ambulatory activity and oxygen consumption in UN offspring during ad libitum feeding. Maternal undernutrition triggers developmental changes in the hypothalamus in utero which were further affected by adequate feeding after birth during the postnatal period by affecting GHSR signaling. The GHSR contributes to the hyperphagia and the increase in body weight when maternal undernutrition is followed by an obesity prone life environment.     

A chemically derived milk substitute that is compatible with mouse milk for artificial rearing of mouse pups.

The object of this study was to prepare a chemically derived milk substitute that is compatible with mouse-milk. Milk was independently collected from ICR, BALB/c, and FVB/N mice, and analyzed for the protein, fat, and mineral contents to formulate a milk substitute. Thereafter, ICR mouse pups were artificially reared on the milk substitute to evaluate the rate of increase of their body weights. A gastric cannula tube was placed through the esophageal way into 8-day-old ICR pups, and the mice were fed with the milk substitute by computer-regulated infusion pumping by the pup-in-a-cup method. The analytical mean values of total protein and total fat in milk from ICR, BALB/c, and FVB/N mice were 10.23 +/- 0.49% and 21.34 +/- 1.31%, respectively. The milk substitute was constituted from purified bovine casein and whey proteins, five edible oils, including MCT oil, minerals, and vitamins. After 8 days of artificial rearing with the new milk substitute, 36 of the 42 pups had survived, and the growth rate of these mice was not significantly different from that of maternally reared littermate pups. In conclusion, we have succeeded in the preparation of a chemically derived milk substitute for mice pups which is available for clarifying the roles of dietary components such as milk-bone substance during the suckling period in mice pups including those of knockout and transgenic mice.     

Maternal immunization with pneumococcal surface protein A protects against pneumococcal infections among derived offspring

Pathogen-specific antibody plays an important role in protection against pneumococcal carriage and infections. However, neonates and infants exhibit impaired innate and adaptive immune responses, which result in their high susceptibility to pneumococci. To protect neonates and infants against pneumococcal infection it is important to elicit specific protective immune responses at very young ages. In this study, we investigated the protective immunity against pneumococcal carriage, pneumonia, and sepsis induced by maternal immunization with pneumococcal surface protein A (PspA). Mother mice were intranasally immunized with recombinant PspA (rPspA) and cholera toxin B subunit (CTB) prior to being mated. Anti-PspA specific IgG, predominantly IgG1, was present at a high level in the serum and milk of immunized mothers and in the sera of their pups. The pneumococcal densities in washed nasal tissues and in lung homogenate were significantly reduced in pups delivered from and/or breast-fed by PspA-immunized mothers. Survival after fatal systemic infections with various types of pneumococci was significantly extended in the pups, which had received anti-PspA antibody via the placenta or through their milk. The current findings strongly suggest that maternal immunization with PspA is an attractive strategy against pneumococcal infections during early childhood.     

Effects of In utero environment and maternal behavior on neuroendocrine and behavioral alterations in a mouse model of prenatal trauma

Maternal posttraumatic stress disorder (PTSD) following trauma exposure during pregnancy is associated with an increased risk of affective disorders in children. To investigate the mechanisms by which prenatal trauma and/or maternal PTSD affect brain development and behavior we established a mouse model of prenatal traumatic (PT) experience based on the application of an electric foot shock to C57Bl/6N female mice on the gestational day 12 during their pregnancy. The model is based on a previously validated animal model of PTSD. We found high anxiety levels and poor maternal care along with reduced serum prolactin and increased corticosterone levels in dams following maternal trauma (MT). PT‐pups were born smaller and stayed smaller throughout their life. We show increased time and frequency of ultrasonic calls in PT‐pups when separated from the mothers on the postnatal day (PND) 9. Cross‐fostering experiments reveal lower anxiety levels in PT pups raised by healthy mothers as compared to trauma‐naive pups raised by MT‐dams. Importantly, the combination of prenatal trauma and being raised by a traumatized mother leads to: (1) the highest corticosterone levels in pups, (2) longest USV‐call time and (3) highest anxiety levels in comparison to other experimental groups. Our data indicates a distinct change in maternal care following MT which is possibly associated with trauma‐induced decrease in prolactin levels. Furthermore, we show that maternal behavior is crucial for the development of the offspring anxiety and specific aspects in maternal care overwrite to a significant extend the effects of in utero and postnatal environment. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 76: 1254–1265, 2016     

Impact of maternal stress on the transmammary transfer and protective capacity of herpes simplex virus-specific immunity

In adults, psychological stress regulates immune responsiveness in part via the increased levels of corticosterone that are produced as a result of hypothalamic-pituitary-adrenal (HPA) axis activation. However, there is a lack of knowledge as to the role such regulation may play in the neonate. Neonates are severely compromised in their ability to generate an immune response to pathogens encountered after birth and therefore rely heavily on maternally derived antibody acquired postnatally through the milk. This passive transfer of antibody is critical for protection of the neonate from severe herpes simplex virus (HSV) infection and mortality. Using a well-established postnatal restraint/light stress model, we determined whether maternal stress and the associated increases in corticosterone would affect the transmammary transfer of antibody and subsequent neonate susceptibility to HSV-associated mortality. Serum corticosterone levels were markedly increased in lactating mice subjected to the restraint/light stress, and increased levels of corticosterone were transferred through the milk of these stressed mothers to their neonates. Despite these increases in corticosterone, the transmammary transfer and accumulation of total and HSV-specific IgG in neonate serum remained intact. This milk-derived, HSV-specific antibody alone protected the neonate from systemic viral spread. Interestingly, postnatal maternal stress significantly increased neonate survival after HSV-2 infection despite no apparent alteration in viral spread. These studies demonstrate that although the transmammary transfer of antibody is unaffected by maternal stress, stress may be enhancing components of antiviral immunity that are effective in protecting neonates from HSV-associated mortality.     

The experience of maternity exerts a significant effect on the shaping of behavior in rat progeny in early postnatal ontogeny]

Maturation of specific behavioral reactions were studied in 13-24-day-old rats born by females with prior maternal experience (group A) and maternally naive females (group B). The rats of group B showed later eyes opening and earlier maturation of grooming and manipulation than the group A rats. The development of behavioral reactions was found to be related with eye opening in the rats of group A and maturation of manipulation in group B rats. The results suggest that the maternal influence is a significant environmental factor, which affects the early postnatal development of rat pups.     

Prenatal exposure to thyroid hormone is necessary for normal postnatal development of murine heart and lungs

Maternal hypothyroxinemia during early pregnancy poses an increased risk for poor neuropsychological development of the fetus. We tested the hypothesis that maternal hypothyroidism before the onset of fetal thyroid function also affects postnatal development of heart and lungs. This question was addressed in transgenic mice that express herpes simplex virus thymidine kinase in their thyroidal follicle cells. Treatment with ganciclovir rendered these mice severely hypothyroid because viral thymidine kinase converts ganciclovir into a cytotoxic nucleoside analog. Since ganciclovir crosses the placenta, it also destroyed the thyroid of transgenic embryos while leaving the thyroids of nontransgenic littermates unaffected. Hypothyroidism of both mother and fetus did not affect prenatal heart and lung development. However, the postnatal switch from beta- to alpha-myosin heavy chain (beta- and alpha-MHC, respectively) gene expression and the increase of SERCA-2a mRNA expression did not occur in the ventricular myocardium of either the transgenic (thyroid destroyed) or nontransgenic (intact thyroid) offspring of hypothyroid mothers. Similarly, postnatal animals of the latter two groups retained elevated surfactant protein (SP) A, B, and C mRNA levels in their alveolar epithelium. In hypothyroid pups from hypothyroid mothers, these changes were accompanied by decreased alveolar septation. Our study shows that these effects of maternal hypothyroidism become manifest after birth and are aggravated by the concomitant existence of neonatal hypothyroidism.     

Impaired Maternal Behavior in Usp46 Mutant Mice: A Model for Trans-Generational Transmission of Maternal Care

Usp46 mutant mice (congenic strain on a B6 genetic background; MT mice) have a low weaning rate and display poor maternal behavior compared to C57BL/6J mice (B6 mice). Based on these observations, we examined how maternal behavior is shaped by cross-fostering and in-fostering MT and B6 mice. The experiments consisted of six groups: B6 mice fostered by their biological mother (B6-CO); MT mice fostered by their biological mother (MT-CO); B6 mice fostered by a different B6 mother (B6-IF); MT mice fostered by a different MT mother (MT-IF); B6 mice fostered by an MT mother (B6-CF); and MT mice fostered by a B6 mother (MT-CF). Maternal behavior was assessed using the pup-retrieval test in adult female offspring, and four parameters, time nursing pups in the nest, time sniffing or licking pups, rearing behavior, and latency to retrieve pups, were measured. Cross-fostering significantly reduced time spent nursing and sniffing/licking pup, and increased the number of instances of rearing in the B6-CF group, and improved three parameters of maternal behaviors (nursing, rearing and latency) in the MT-CF group. These results indicate that the level of maternal care is transmitted to their pups and proper maternal behaviors can be shaped if adequate postpartum maternal care is given, even in genetically vulnerable mice. However, the offspring’s genotype may also influence the development of maternal behaviors in adulthood. Thus, MT mice may prove useful as a model for trans-generational transmission of maternal care, and these findings may provide insight into the mechanisms of maltreating behaviors in human child abuse.     

Littermate Influence on Infant Growth in Mice: Comparison of SJL/J and ICR as Cotransferred Carrier Embryos

In mice, a minimum number of healthy embryos is required to trigger and maintain pregnancy. Therefore, when recovering mouse embryos from a limited litter, one useful technique is to transfer carrier ICR embryos along with the embryos of interest, a technique referred to as cotransfer. In this study, we examined suitable mouse strains for cotransfer with C57BL/6J (B6) embryos in regards to the maintenance of pregnancy, number of pups born, intrauterine growth, and postnatal growth. Because the coat color of B6 is black, we compared two white coat-colored strains, SJL/J and ICR. Cotransfer of SJL/J and ICR embryos had similar effects on maintenance of pregnancy, number of pups born, and intrauterine growth. However, the postnatal growth of B6 mouse pups cotransferred and grown with SJL/J pups was better than for B6 mouse pups cotransferred and grown with ICR pups, suggesting competition among littermates. These results demonstrate that cotransfer of SJL/J embryos will be useful not only as carrier embryos with B6-background embryos but also as a model system to examine littermate competition.