The individuality of mice

Mutant mice simulating human CNS disorders are used as models for therapeutic drug development. Drug evaluation requires a coherent correlation between behavioral phenotype and drug status. Variations in behavioral responses could mask such correlations, a problem highlighted by the three-site studies of Crabbe et al. (1999) and Wahlsten et al. (2003a). Factors contributing to variation are considered, focusing on differences between individual animals. Genetic differences due to minisatellite variation suggest that each mouse is genetically distinct. Effects during gestation, including maternal stress, influence later life behavior; while endocrine exchanges between fetus and parent, and between male and female fetuses dependent on intrauterine position, also contribute. Pre and perinatal nutrition and maternal attention also play a role. In adults, endocrine cyclicity in females is a recognized source of behavioral diversity. Notably, there is increasing recognition that groups of wild and laboratory mice have complex social structures, illustrated through consideration of Crowcroft (1966). Dominance status can markedly modify behavior in test paradigms addressing anxiety, locomotion and aggressiveness, to an extent comparable to mutation or drug status. Understanding how such effects amplify the behavioral spectrum displayed by otherwise identical animals will improve testing.     

A keratin K5Cre transgenic line appropriate for tissue-specific or generalized Cre-mediated recombination

We describe here a mouse line bearing a bovine keratin K5Cre recombinase transgene. These mice showed a dual pattern of Cre-mediated recombination, depending on the parent transmitting the transgene. In paternal transmission, recombination occurred specifically in the skin and stratified epithelia-as expected according to the expression of endogenous keratin K5. However, constitutive recombination between loxP sites transmitted by the sperm took place when the mother possessed the K5Cre transgene, even when the transgene was absent in the progeny. Cre expression in late-stage oocytes, with the Cre protein persisting into the developing embryo, leads to the constitutive recombination observed. Thus, this transgenic line allows for both tissue-specific and generalized recombination, depending on the breeding scheme.     

土壤干旱对元宝枫渗透调节能力的影响

采用盆栽控水法和P—V技术研究分析了不同土壤干旱(速度、程度)条件对元宝枫渗透调节能力的影响。结果表明,元宝枫具有很强的渗透调节能力．但该能力受土壤干旱的速度和程度影响,在缓慢干旱条件下,元宝枫叶片的ψw、ψ0、π100、RWC^0、ROWC^0均明显降低．其中与渗透调节能力直接相关的(π100可下调0．52MPa,ψ0下调1．51MPa。在快速干旱条件下π100和ψ0分别仅下凋0．20MPa和0．48MPa。△π100值也表明缓慢干旱条件下元宝枫渗透调节能力是快速干旱下的45倍。在缓慢干旱条件下．由轻度到中度干旱时其渗透调节能力显著增强(增加270％);由中度到严重干旱时．增加不明显(增加了24．5％)。从3种有机渗透调节物质含量与△π100值的动态变化可见,可溶性糖含量增加对渗透调节能力的贡献是第一位的．其次是Pro、游离氨基酸。     

Obtaining mice that carry human mitochondrial DNA transmitted to the progeny

To study human diseases associated with mutations in mitochondrial DNA one needs an animal model in which the distribution of abnormal mtDNA and its impact on the phenotype might be followed. We isolated human mitochondria from HepG2 cell culture and microinjected them into murine zygotes, upon which those were transplanted to the pseudopregnant mice. PCR with species-specific primers allowed detecting human mtDNA in the tissues of 7-13-day embryos. No serious alterations in the development of transmitochondrial embryos were noticed. Among various organs/tissues of the 13-day embryos, human mtDNA was detected only in the heart, skeletal muscles, and stomach, which is in line with its uneven distribution among the blastomeres of an early mouse embryo that we described previously. In four recipient females, the microinjected zygotes were allowed to develop to term, the four neonate males of their joint litter were sacrificed, and in three of them human mtDNA was detected in the heart, skeletal muscles, stomach, brain, testes, and bladder. Six females of that joint litter were grown and mated to intact males. In the progeny (F1) of one of the females two mice were carrying human mtDNA in the heart, skeletal muscles, stomach, brain, lungs, uterus, ovaries, and kidneys. The study confirms the possibility to obtain transmitochondrial mice carrying human mtDNA that is transmitted to the animals of the next generation. Our results also indicate that among the organs to which human mtDNA is distributed some are more likely to receive it than others.     

Maternal effects on offspring depend on female mating pattern and offspring environment in yellow dung flies

Abstract Direct costs and benefits to females of multiple mating have been shown to have large effects on female fecundity and longevity in several species. However, with the exception of studies examining genetic benefits of polyandry, little attention has been paid to the possible effects on offspring of multiple mating by females. We propose that nongenetic effects of maternal matings on offspring fitness are best viewed in the same context as other maternal phenotype effects on offspring that are well known even in species lacking parental care. Hence, matings can exert effects on offspring in the same way as other maternal environment variables, and are likely to interact with such effects. We have conducted a study using yellow dung flies ( Scathophaga stercoraria ), in which we independently manipulated female mating rate, number of mates and maternal thermal environment and measured subsequent fecundity, hatching success, and offspring life-history traits. To distinguish between direct effects of matings and potential genetic benefits of polyandry we split broods and reared offspring at three different temperature regimes. This allowed us to demonstrate that although we could not detect any simple benefits or costs to matings, there are effects of maternal environment on offspring and these effects interact with female mating regime affecting offspring fitness. Such interactions between female phenotype and the costs and benefits of matings have potentially broad implications for understanding female behavior.     

The evolution of sexual size dimorphism in the house finch. V. Maternal effects

The phenotype of a mother and the environment that she provides might differentially affect the phenotypes of her sons and daughters, leading to change in sexual size dimorphism. Whereas these maternal effects should evolve to accommodate the adaptations of both the maternal and offspring generations, the mechanisms by which this is accomplished are rarely known. In birds, females adjust the onset of incubation (coincident with the first egg or after all eggs are laid) in response to the environment during breeding, and thus, indirectly, determine the duration of offspring growth. In the two house finch (Carpodacus mexicanus) populations that breed at the extremes of the species' distribution (Montana and Alabama), females experience highly distinct climatic conditions during nesting. We show that in close association with these conditions, females adjusted jointly the onset of incubation and the sequence in which they produced male and female eggs and consequently modified the growth of sons and daughters. The onset of incubation in newly breeding females closely tracked ambient temperature in a pattern consistent with the maintenance of egg viability. Because of the very different climates in Montana and Alabama, females in these populations showed the opposite patterns of seasonal change in incubation onset and the opposite sex bias in egg-laying order. In females with breeding experience, incubation onset and sex bias in laying order were closely linked regardless of the climatic variation. In nests in which incubation began with the onset of egg laying, the first-laid eggs were mostly females in Montana, but mostly males in Alabama. Because in both populations, male, but not female, embryos grew faster when exposed to longer incubation, the sex-bias produced highly divergent sizes of male and female juveniles between the populations. Overall, the compensatory interaction between the onset of incubation and the sex-biased laying order achieved a compromise between maternal and offspring adaptations and contributed to rapid morphological divergence in sexual dimorphism between populations of the house finch breeding at the climatic extremes of the species range.     

Dynamic reprogramming of DNA methylation in the early mouse embryo.

Dynamic epigenetic modification of the genome occurs during early development of the mouse. Active demethylation of the paternal genome occurs in the zygote, followed by passive demethylation during cleavage stages, and de novo methylation, which is thought to happen after implantation. We have investigated these processes by using indirect immunofluorescence with an antibody to 5-methyl cytosine. In contrast to previous work, we show that demethylation of the male pronucleus is completed within 4 h of fertilisation. This activity is intricately linked with and not separable from pronucleus formation. In conditions permissive for polyspermy, up to five male pronuclei underwent demethylation in the same oocyte. Paternal demethylation in fertilised oocytes deficient for MBD2, the only candidate demethylase, occurred normally. Passive loss of methylation occurred in a stepwise fashion up to the morulae stage without any evidence of spatial compartmentalisation. De novo methylation was observed specifically in the inner cell mass (ICM) but not in the trophectoderm of the blastocyst and hence may have an important role in early lineage specification. This is the first complete and detailed analysis of the epigenetic reprogramming cycle during preimplantation development. The three phases of methylation reprogramming may have roles in imprinting, the control of gene expression, and the establishment of nuclear totipotency.     

The inheritance of modifiers conferring self-fertility in the partially self-incompatible perennial, Campanula rapunculoides L. (Campanulaceae)

The role of partial self-incompatibility in plant breeding system evolution has received little attention. Here, we examine the genetic basis of modifiers conferring self-fertility in the creeping bellflower, Campanula rapunculoides L. (Campanulaceae), a partially self-incompatible herb. A survey of 35 individuals from two natural populations indicates that 45% of them are strongly self-incompatible, 40% intermediately self-incompatible, and 15% weakly self-incompatible and that some plants show a strong breakdown in self-incompatibility over floral age. We generated 101 F1 families by random crossing among 31 parental plants and estimated the heritability of self-fertility in day 1 and day 4 female-phase flowers, the genetic correlation between day 1 and day 4 self-fertility, and the coefficient of additive genetic variance of self-fertility. We use linear regression and data from additional crosses to examine whether there are significant maternal effects in the expression of self-fertility. We use Fain's test to determine if a major gene influences self-fertility and, finding no evidence, use data from additional crosses on an F2 generation to estimate the mean number and dominance of genes conferring self-fertility. These analyses indicate that the heritability (h2) of self-fertility is 0.24 in day 1 female-phase flowers and 0.44 in day 4 flowers, self-fertility is primarily additive but shows some recessive effects, and self-fertility is estimated to be controlled by four genetic factors. In addition, we have evidence that there may be maternal effects for self-fertility, especially for weakly self-incompatible plants. The significance of these results in the context of mating system evolution is discussed.     

Inbreeding and true seed in tetrasomic potato. IV. Synthetic cultivars

A true potato seed (TPS) synthetic cultivar from open pollination may broaden the genetic base in potato. A synthetic cultivar can also reduce the effect of inbreeding and maintain the productivity from generation to generation. Selected tetraploid parental genotypes, based on combining-ability tests, were chosen for isolated polycrosses to obtain tetraploid offspring. A series of experiments were undertaken to investigate the development of these TPS synthetic populations in two Peruvian locations: San Ramon, a rainfed, humid, mid-altitude environment, and La Molina, an arid, coastal environment under irrigation. Natural open-pollinated synthetics or control-mixture synthetics, involving two to six parents, had a similar tuber set but plant survival and tuber weight were higher in control synthetics including two or six parents. The results suggest that two-parent open-pollinated TPS synthetics may be a feasible option by selecting the right parents for the base population. A subsequent experiment showed that four-parent control synthetics (i.e. double crosses) were the best for tuber weight and size, followed by the two-parent control synthetics. Synthetic breeding populations could be shared with other breeders, who in cooperation with their local farmers may select promising genotypes for further cultivar release. Received: 15 December 2000 / Accepted: 4 April 2001