Induction of paternal genome loss by the paternal-sex-ratio chromosome and cytoplasmic incompatibility bacteria (Wolbachia): A comparative study of early embryonic events

Paternal genome loss (PGL) during early embryogenesis is caused by two different genetic elements in the parasitoid wasp, Nasonia vitripennis. Paternal sex ratio (PSR) is a paternally inherited supernumerary chromosome that disrupts condensation of the paternal chromosomes by the first mitotic division of fertilized eggs. Bacteria belonging to the genus Wolbachia are present in Nasonia eggs and also disrupt paternal chromosome condensation in crosses between cytoplasmically incompatible strains. Cytoplasmic incompatibility Wolbachia are widespread in insects, whereas PSR is specific to this wasp. PGL results in production of male progeny in Nasonia due to haplodiploid sex determination. The cytological events associated with PGL induced by the PSR chromosome and by Wolbachia were compared by fluorescent light microscopy using the fluorochrome Hoescht 33258. Cytological examination of eggs fertilized with PSR-bearing sperm revealed that a dense paternal chromatin mass forms prior to the first metaphase. Quantification of chromatin by epifluorescence indicates that this mass does undergo replication along with the maternal chromatin prior to the first mitotic division but does not replicate during later mitotic cycles. Contrary to previous reports using other staining methods, the paternal chromatin mass remains condensed during interphase and persists over subsequent mitotic cycles, at least until formation of the syncytial blastoderm and cellularization, at which time it remains near the center of the egg with the yolk nuclei. Wolbachia-induced PGL shows several marked differences. Most notable is that the paternal chromatin mass is more diffuse and tends to be fragmented during the first mitotic division, with portions becoming associated with the daughter nuclei. Nuclei containing portions of the paternal chromatin mass appear to be delayed in subsequent mitotic divisions relative to nuclei free of paternal chromatin. Crosses combining incompatibility with PSR were cytologically similar to Wolbachia-induced PGL, although shearing of the paternal chromatin mass was reduced. Wolbachia may, therefore, block an earlier stage of paternal chromatin processing in the fertilized eggs than does PSR. © 1995 Wiley-Liss, Inc.     

EVOLUTION OF INCOMPATIBILITY-INDUCING MICROBES AND THEIR HOSTS

In many insect species, males infected with microbes related to Wolbachia pipientis are “incompatible” with uninfected females. Crosses between infected males and uninfected females produce significantly fewer adult progeny than the other three possible crosses. The incompatibility-inducing microbes are usually maternally transmitted. Thus, incompatibility tends to confer a reproductive advantage on infected females in polymorphic populations, allowing these infections to spread. This paper analyzes selection on parasite and host genes that affect such incompatibility systems. Selection among parasite variants does not act directly on the level of incompatibility with uninfected females. In fact, selection favors rare parasite variants that increase the production of infected progeny by infected mothers, even if these variants reduce incompatibility with uninfected females. However, productivity-reducing parasites that cause partial incompatibility with hosts harboring alternative variants can be favored once they become sufficiently abundant locally. Thus, they may spread spatially by a process analogous to the spread of underdominant chromosome rearrangements. The dynamics of modifier alleles in the host are more difficult to predict, because such alleles will occur in both infected and uninfected individuals. Nevertheless, the relative fecundity of infected females compared to uninfected females, the efficiency of maternal transmission and the mutual compatibility of infected individuals all tend to increase under within-population selection on both host and parasite genes. In addition, selection on host genes favors increased compatibility between infected males and uninfected females. Although vertical transmission tends to harmonize host and parasite evolution, competition among parasite variants will tend to maintain incompatibility.     

Expression of sunflower low-molecular-weight heat-shock proteins during embryogenesis and persistence after germination: localization and possible functional implications

We isolated and sequenced Ha hsp 17.9, a DNA complementary (cDNA) of dry-seed stored mRNA that encodes a low-molecular-weight heat-shock protein (LMW HSP). Sequence analysis identified Ha hsp17.9, and the previously reported Ha hsp17.6, as cDNAs encoding proteins (HSP17.6 and HSP17.9) which belong to different families of cytoplasmic LMW HSPs. Using specific antibodies we observed differential expression of both proteins during zygotic embryogenesis under controlled environment, and a remarkable persistence of these LMW HSPs during germination. Immuno-blot analysis of HSP17.9 proteins in two-dimensional gels revealed that the polypeptides expressed in embryos were indistinguishable from LMW HSPs expressed in vegetative tissues in response to water deficit; but they appeared different from homologeous proteins expressed in response to thermal-stress. Tissue-print immunolocalization experiments showed that HSP17.9 and HSP17.6 were homogeneously distributed in every tissue of desiccation-tolerant dry seeds and young seedlings under non-stress conditions. These results demonstrate developmental regulation of specific, cytoplasmic, plant LMW HSPs, suggesting also their involvement in water-stress tolerance.     

Protein expression of a self-compatible allele from Lycopersicon peruvianum: introgression and behavior in a self-incompatible background

Lycopersicon peruvianum (wild tomato) is a gametophytic self-incompatible (SI) species. One natural population has been shown to harbor a self-compatible (SC) allele. A stylar protein associated with the self-compatibility allele has been elucidated using SDS-PAGE. The temporal and spatial expression of this protein is presented and compared with protein expression of two SI alleles. Hybrids containing the SC and SI alleles were used in a backcrossing program to introgress the SC allele into SI backgrounds in six independent lines. Controlled pollinations and SDS-PAGE were used to identify and select classes of progeny. After four backcross generations (approximately 97% recovery of the SI backgrounds) the SC allele still confers self-fertility in lines that contain this allele, providing evidence that the mutation to SC occurred at the S-locus and that the associated protein is likely responsible.     

Distinct morphological and mito-inhibitory effects induced by TGF-β1, HGF and EGF on mouse,rat and human hepatocytes

TGF-1 is known as a potent inhibitor of proliferation of rat and human hepatocytes. In this study we show that the effects of TGF-1 are quite different on mouse hepatocytes. In rat and human hepatocytes, TGF-1 inhibited DNA synthesis and also inhibited the morphological changes induced by growth factors in rat and human hepatocytes. In contrast, addition of TGF-1 to mouse hepatocytes resulted in pronounced alterations in morphology of these cells. These changes were similar to those induced by HGF and EGF. The induction of structural changes by TGF-1 was noted only in mouse hepatocytes. Mouse hepatocytes were also much more resistant to the mito-inhibitory effect of TGF-1. These findings suggest profound differences in hepatocyte growth regulation between these species and may relate to observed differences in susceptibility to carcinogenesis.Abbreviations EGF epidermal growth factor - HGF hepatocyte growth factor - SF scatter factor - TGF-1 transforming growth factor beta type one     

用荧光指示剂Fura－2测定正常和电刺激后蛙肌胞浆自由Ca~（2＋）浓度

蛙半腱肌肌束负载Ｆｕｒａ－２／ＡＭ后,可用荧光信号Ｆ３４０、３８０ｎｍ波长比值（Ｒ３４０／３８０）反映胞浆内游离Ｃａ２＋浓度（〔Ｃａ２＋〕）。利用这一技术,我们发现长时间电刺激后的骨骼肌〔Ｃａ２＋〕,高于未刺激肌,Ｒ３４０／３８０分别为１．４９±０．５４（ｎ＝１０）和１．０２±０．２６（ｎ＝１０）。加入Ｃａ２＋载体伊屋诺霉素（ｉｏｎｏｍｙｃｉｎ,１μｍｏｌ／Ｌ）后,正常肌与电刺激肌〔Ｃａ２＋〕,均上升,但刺激肌上升幅度低,持续时间短。说明电刺激至力竭后,细胞内有较多的Ｃａ２＋负载。增加细胞外Ｃａ２＋浓度至１５ｍｍｏｌ／Ｌ,〔Ｃａ２＋〕ｉ下降。而给予Ｎａ＋－Ｃａ２＋交换阻断剂奎尼丁（１０４ｍｏｌ／Ｌ）后,正常肌〔Ｃａ２＋〕ｉ上升,刺激肌〔Ｃａ２＋〕ｉ下降。结果提示：Ｎａ＋－Ｃａ２＋交换是正常骨胳肌外排Ｃａ２＋的途径之一;而长时间肌肉活动则可能使细胞膜Ｎａ＋－Ｃａ２＋交换方式改变,从而导致力竭肌〔Ｃａ２＋〕ｉ上升。