Postpollination-prezygotic ovular secretions into the micropylar canal inPseudotsuga menziesii (Pinaceae)

Ovular morphology was examined ultrastructurally inPseudotsuga menziesii to determine the effects of the ovule on pollen development. Vesicles containing lipid-like substances traverse cell walls of the inner epidemis of the integument and release their contents at the integument surface to form the integumentary membrane. A major aqueous secretion from the integument into the micropylar canal is proposed to occur by the movement of the integumentary membrane and its invaginations towards the center of the micropylar canal. The cellular degeneration of the nucellar apex results from the breakdown of vacuoles. After this degeneration, electron-dense substances move from the prothallial cells of the female gametophyte towards the nucellus, and many morphological changes in the nucellus, prothallial cells, and micropylar canal take place simultaneously. We interpret these changes to result from another major secretion from the prothallial cells. Egg cytoplasm appears to disorganize for a short time. Simultaneously, substantial amounts of electron dense-substances in the prothallial cells and lipid-like substances in surface cell walls of the female gametophyte move towards the nucellus as components of the third major secretion.     

Neurotrophin-3 as an essential signal for the developing nervous system

Rapid advances in characterization of the biological actions mediated by the third member of the neurotrophin family, neurotrophin-3 (NT-3), have been made recently in vitro as well asin situ. These have been made possible by the cloning of the genes for NT-3 and for its transducing receptor tyrosine kinase TrkC. This article will focus on the roles of NT-3 in the nervous system.In situ localization of NT-3 consistent with that of its receptor is manifested at all developmental stages studied and into adulthood. Through TrkC, NT-3 signals a number of trophic effects, ranging from mitogenesis, promotion of survival, or differentiation, depending on the developmental stage of the target cells. The sites of action of NT-3 reside primarily in the peripheral nervous system (PNS), various areas of the central nervous system (CNS), and in the enteric nervous system (ENS). Analyses of the phenotypes of transgenic mice lacking NT-3 or injection of embryos with a blocking antibody have so far revealed the essential role of NT-3 in development of specific populations of the PNS, and in particular of proprioceptive, nodose, and auditory sensory neurons and of sympathetic neurons. The actions of NT-3 also extend to modulation of transmitter release at several types of synapses in the periphery as well as in the adult CNS. In addition, NT-3 may play a role in the development of tissues other than the nervous system, such as the cardiovascular system. Future investigations will widen the understanding of the many roles of NT-3 on both neuronal and nonneuronal cells.     

Human placental alkaline phosphatase as a histochemical marker of gene expression in transgenic mice

The human placental alkaline phosphatase (PLAP) gene was analysed for its utility as a histochemically detectable reporter gene in transgenic mice. A reporter gene was made by linking the PLAP structural gene to an enhancerpromoter element from the human -actin gene. This gene was inserted into the mouse genome by transfection of embryonic stem cells, and by microinjection of fertilized eggs. Histochemical staining showed that the transgene was uniformly expressed in four of four stable ES cell lines, and in all ten tissues examined from adult animals from five lines of transgenic mice. Non-transgenic cells did not stain. These results suggest that the human PLAP gene will be of utility in studies requiring phenotypic marking of cells in tissues of mice.     

人ApoE转基因小鼠与TGE_（7－2） TGE_（7－3）转基因鼠系的建立

用含小鼠金属硫蛋白（ＭＴ－１）基因启动子与突变的人ＡｐｏＥ７基因的６．０ＫｂＤＮＡ片段作为目的基因制备转基因小鼠,利用显微注射法将目的基因导入４４１枚受精卵,移植于２０只假孕鼠,其中１５只受孕,共产仔鼠８０只,经ａ－３２Ｐ斑点杂交与Ｓｏｕｔｈｅｒｎ杂交法鉴定出两只整合有人ＡｐｏＥ基因的转基因雌鼠,其拷贝数分别为２和５。将两只首建鼠（雌性Ｆｏ代）与正常雄鼠交配,建立Ｆ１代转基因鼠系ＴＧＥ７－２和ＴＧＥ７－３,为进一步从整体上研究ＡｐｏＥ在脂质代谢中的作用以及ＡｐｏＥ与动脉粥样硬化和Ａｌｚｈｅｉｍｅｒ’ｓ病的关系创造条件。     

Levels of Endogenous lnterleukin-1, Interleukin-6, and Tumor Necrosis Factor in Congenic Mice Infected with Borrelia garinii

This study describes the levels of interleukin-1 alpha (IL-1α), tumor necrosis factor alpha (TNFα) and interleukin-6 (IL-6) in the sera and parenchymal organs of various congenic mouse strains infected with Borrelia garinii. A significant elevation of inflammatory cytokine levels was found in the organs of C3H/HeN (H-2^k) and B10.BR (H-2^k) mice but not in those of BALB/c mice (H-2^d). Focally produced cytokines can contribute to antimicrobial defense against these organisms. High levels of IL-1α were observed in the sera of C3H/HeN, B10.BR and B10 (H-2^b) mice infected with B. garinii and they were associated with the presence of spirochetes in the skin. Thus, susceptible mice demonstrated a stronger cytokine response than resistant mice. This study presents in vivo evidence that B. garinii infection affects the immunopathogenesis of Lyme disease.     

Female genotype affects male success in sperm competition

The central question addressed by most studies of sperm competition is: ''what determines which male''s sperm are used at fertilization?'' Empirical and theoretical studies that address this question have traditionally focused on adaptations which enhance male fertilization success while treating the female as a receptacle in which sperm competition is played out. Here we provide evidence which suggests that female genotype strongly influences the outcome of sperm competition. When the sperm of two males are in competition the proportion of offspring fathered by the second male to mate (P₂) was found to be highly repeatable only if the male pair were mated to three different, but genetically similar females (full-sisters to each other; unrelated to either of the males). In contrast, if a male pair were mated to three females that were unrelated then P₂ was either non-repeatable or marginally repeatable. We also show that male success in sperm competition is determined, to a large extent, by gamete and/or male–female compatibility. This conclusion is derived from the observation that P₂ was repeatable among full-sisters mated to different, yet genetically similar male pairings, whilst P₂ was non-repeatable among full-sisters mated to different, genetically distinct male pairings.     

On the function of female ornaments: male bluethroats prefer colourful females

Female ornaments in animals with conventional sex roles have traditionally been considered non-functional, being merely a genetically correlated response to selection for male ornamentation. Alternatively, female ornaments may be influenced by selection acting directly on the females, either through female–female competition or male choice. We tested the latter hypothesis in mate choice experiments with bluethroats (Luscinia s. svecica), a passerine bird in which females vary considerably in coloration of an ornamental throat patch. In outdoor aviaries placed in prime breeding habitat, males were allowed to choose between a colourful and a drab female. We found that males associated more with, and performed more sexual behaviours towards, colourful females. Female coloration was not age-related, but correlated significantly with body mass and tarsus length. Thus, we have demonstrated both a male preference for female ornamentation, and a relationship between ornament expression and female body size, which may be indicative of quality. Our results refute the correlated response hypothesis and support the hypothesis that female ornamentation is sexually selected.     

Male display rate reveals ejaculate characteristics in the Trinidadian guppy,Poecilia reticulata.

Previous work (Reynolds and Gross 1992) has demonstrated that mate choice enables female guppies, Poecilia reticulata, to obtain heritable benefits (''good genes'') for their offspring. It is not yet known whether males also signal their functional fertility, that is, their viability as fathers, to female guppies. Our study tested the hypothesis that a male''s behaviour reveals characteristics of his ejaculate. We uncovered a strong correlation between display rate and sperm number in male guppies derived from two wild Trinidadian populations. This result indicates that information on the functional fertility of potential mates is available to females. However, our investigation also found a significant relationship between the frequency of sneaky mating and sperm number. Female guppies in wild populations, particularly those experiencing a high predation regime, are constantly subjected to sneaky mating attempts. As the males responsible for these sneaky matings have highest reserves of sperm they may have the capacity to undermine female choice. The implications of these findings for sperm competition are discussed.     

Susceptibility and resistance to pneumococcal disease in mice.

Although pneumococcus is a major pathogen of humans and, every year, the bacterium causes illness and death in millions of individuals, the genetic basis of susceptibility to the bacterium is unknown. Previous attempts to identify the gene explaining differing susceptibility to pneumococcal disease in humans have been without significant success. In order to develop new hypotheses that can be tested in humans, significant efforts have been made using mouse models of infection and disease. Indeed, the majority of the information so far obtained on pneumococcal disease in vivo has come from mouse studies. Mice differ in their response to pneumococcal disease, however, and the genetic basis of susceptibility to infection is unknown. This review summarises the current knowledge of mouse susceptibility and resistance to pneumococcal infection.