Microtubule associated motor proteins of Plasmodium falciparum merozoites.

We have studied the occurrence, stage specificity and cellular location of key molecules associated with microtubules in Plasmodium falciparum merozoites. Antibodies to gamma tubulin, conventional kinesin and cytoplasmic dynein were used to determine the polarity of merozoite microtubules (mt), the stage specificity of the motor proteins and their location during merozoite development. We conclude that the minus ends of the mts are located at their apical pole. Kinesin was present throughout the lifecycle, appearing as a distinct crescent at the apex of developing merozoites. The vast majority of cytoplasmic dynein reactivity occurred in late merogony, also appearing at the merozoite apex. Destruction of mt with dinitroanilines did not affect the cellular location of kinesin or dynein. In invasion assays, dynein inhibitors reduced the number of ring stage parasites. Our results show that both conventional kinesin and cytoplasmic dynein are abundant, located at the negative pole of the merozoite mt and, intriguingly, appear there only in very late merogony, prior to merozoite release and invasion.

Steroidogenesis in human follicles approaching ovulation as judged from assays of follicular fluid.

Human chorionic gonadotrophin (HCG) was given to patients at mid-cycle before the endogenous LH surge. Graafian follicles were aspirated 32-33 h later, before ovulation was expected, and the levels of several steroids in follicular fluid and in matching serum samples were measured by radioimmunoassay. Two types of Graafian follicle were identified at laparoscopy , based on the nature of the oocyte, granulosa cells and follicular fluid withdrawn from the follicles. Some were large, preovulatory and presumably becoming luteinized while others were generally smaller, non-ovulatory and still growing. The concentrations of dehydroepiandrosterone (DHEA) and 17alpha-hydroxypregnenolone (delta5 intermediates), androstenedione and testosterone were higher in non-ovulatory follicles, whereas large follicles usually contained high levels of progesterone, 17alpha-hydroxyprogesterone, pregnenolone and oestradiol-17beta. A cluster analysis of these data grouped follicles into two distinct clusters, which accorded with their identification as ovulatory or non-ovulatory at laparoscopy. Levels of progesterone, 17alpha-hydroxyprogesterone and oestradiol-17beta in follicular fluid were high in preovulatory follicles in comparison with plasma. Results in two patients indicated that plasma levels of these steroids were determined by the preovulatory follicle. Levels of plasma delta5 steroids were closer to follicular fluid concentrations, whereas DHEA was higher in plasma. The role of the theca and granulosa is discussed in relation to the synthesis of progesterone and oestradiol-17beta in follicles as ovulation approaches.

Steroidogenesis in preovulatory follicles of patients given human menopausal and chorionic gonadotrophins as judged by the radioimmunoassay of steroids in follicular fluid.

The administration of human menopausal gonadotrophin (HMG) followed by human chorionic gonadotrophin (HCG) stimulated the development of various numbers of follicles in patients treated for infertility. Graafian follicles from these patients were aspirated 32-33 h after the injection of HCG and the levels of steroids in the follicular fluid and matching serum samples were measured by radioimmunoassay. The follicles could not be grouped into two distinct clusters as found in patients given HCG during the menstrual cycle but a broad classification of follicles into four groups was indicated from the dendrogram. Two of the groups were similar to the ovulatory and non-ovulatory groups found previously, whereas the other two groups of follicles were more intermediate in nature. The use of a discriminant analysis showed that these two groups had clearly been stimulated by the HMG and HCG, although they were not yet fully ovulatory. Our data indicate that the number of developing follicles is considerably increased by treatment with HMG and HCG but there is asynchrony in follicular development because the pattern of steroid synthesis differs in many follicles. The effects of this asynchronous development on oocyte maturation and disorders of the luteal phase are discussed.

Steroidogenesis by cultured granulosa cells aspirated from human follicles using pregnenolone and androgens as precursors.

Human granulosa cells from Graafian follicles aspirated 3-4 h before the expected time of ovulation were incubated with various steroid substrates, including pregnenolone, androstenedione, testosterone and dehydroepiandrosterone (DHA). Steroid production after 3 and 10 h of incubation was determined by radioimmunoassay. Progesterone and 17alpha-hydroxyprogesterone were the major products of granulosa cells in control short-term cultures with endogenous substrates. The addition of pregnenolone increased the synthesis of progesterone and 17alpha-hydroxyprogesterone compared with the controls, although the response varied considerably between paired short-term cultures. Little or no oestradiol-17beta was produced from endogenous precursors or short-term cultures to which pregnenolone had been added; one follicle, however, produced similar amounts of oestradiol-17beta in the control cultures and after incubation with pregnenolone. When granulosa cells were cultured with various amounts of androstenedione, DHA or testosterone, large amounts of oestradiol-17beta were produced, especially in short-term cultures in which larger amounts of substrate were added. Progesterone production continued and progesterone was synthesized more rapidly or in greater amounts in some short-term test cultures than in the controls. The results indicate that human granulosa cells are one source of oestradiol-17beta during the preovulatory phase. The data support the two-cell theory for oestradiol synthesis, for granulosa cells do not appear to undertake steroid conversion via the 5-unsaturated pathway, but aromatize androgens known to be produced by thecal cells. It is also suggested that either androgens or oestradiol-17beta stimulate progesterone production by granulosa cells, at least in vitro.

Inhibitory activity of the anti-malarial atovaquone (566C80) against ookinetes, oocysts, and sporozoites of Plasmodium berghei.

Ookinete formation from mature Plasmodium berghei gametocytes in vitro was partially inhibited by 0.05-0.1 microM atovaquone and almost totally blocked at a concentration of 0.25 microM. Microgametocyte exflagellation was not affected by atovaquone at concentrations up to 300 microM. Ookinete formation was also inhibited in culture when addition of 0.20 microM atovaquone was delayed by 4 hr, by which time DNA replication was likely to have been completed. Inhibition of ookinete formation by atovaquone was not reversed by orotic acid. Plasmodium berghei-infected Anopheles stephensi mosquitoes were fed a second blood meal 4, 7, 14, and 20 days postinfection (p.i.) from mice that had been treated with atovaquone or control diluent 8 hr previously. Atovaquone blood feeds on day 4 reduced oocyst numbers on days 6-12, although sporozoite numbers in the thorax and abdomen on day 20 were not significantly reduced. Blood feeds on day 7 slowed oocyst growth, blood feeds on day 14 did not significantly reduce sporozoite numbers, and feeds to mosquitoes on day 20 p.i. had no effect on transmission to naive mice. Sporozoite invasion of human hepatoma cells was unaffected by the presence of atovaquone.

An autoradiographic study of gonadotrophin regulation of labelled glycoconjugates within preovulatory mouse follicles during the final stages of oocyte maturation, using [3H]glucosamine as the radioactive precursor.

Immature mice were treated with PMSG and hCG to induce follicular development and ovulation. [3H]Glucosamine was injected at the same time as the PMSG or 2 h before autopsy. The synthesis and distribution of labelled glycoconjugates within the preovulatory follicles was hormonally dependent. PMSG stimulated a rapid uptake of [3H]glucosamine into the zona pellucida and follicular fluid of the largest antral follicles although labelled macromolecules could not be demonstrated in any of the cellular components of these follicles. The injection of hCG stimulated a rapid incorporation of labelled macromolecules into the cellular components of the preovulatory follicle, namely into thecal, granulosa and especially the cumulus cells surrounding the oocyte. The density of labelled macromolecules within the follicular fluid also increased, while the specific and uniform labelling of the zona pellucida which was so characteristic of the period of PMSG stimulation changed. Between 4 and 8 h after the injection of hCG, labelled glycoconjugates containing [3H]glucosamine, became increasingly associated with the outer surface of the zona pellucida and with the region of the egg plasma membrane, even in Graafian follicles not destined to ovulate. The change in distribution of labelled macromolecules on the zona surface may be a prerequisite for successful sperm-zona binding and the specific association of labelled glycoconjugates in the region of the egg plasma membrane may be involved in the preparation of the egg surface for sperm-egg interactions involving cortical granule exocytosis and the block to polyspermy.

A histochemical study of the changes occurring in the protein-carbohydrate composition of the cumulus-oocyte complex and zona pellucida in immature mice in response to gonadotrophin stimulation.

A histochemical account is presented of the changes that occur in the protein-carbohydrate composition of the cumulus-oocyte complex in immature mice after gonadotrophin treatment. The distribution and nature of the glycosaminoglycans (GAG) present was established by enzymic digestion of tissue sections with testicular of Streptomyces hyaluronidase prior to staining with periodic-acid Schiff (PAS) or Alcian Blue. Treatment with exogenous gonadotrophins [pregnant mare's serum and human chorionic gonadotrophin (hCG)] induced gross changes in the appearance of the zona pellucida (and in the histochemical staining of the cumulus-oocyte complex). A reduction was observed in the amount of PAS-positive material present within the zona pellucida of oocytes located in large Graafian follicles examined 40 h after stimulation with pregnant mare's serum. After the injection of hCG, the zona pellucida was further depleted of PAS-positive material. Most of the PAS-positive material became confined to the plasma membrane of the oocyte, while the oocyte itself also became increasingly PAS-positive. All the GAGs disappeared from zona pellucida within 4 h of hCG stimulation. The changes observed in the protein-carbohydrate composition of the zona pellucida in preovulatory oocytes immediately prior to ovulation may be a prerequisite for successful sperm-egg interactions.

Corpus luteum function in ageing inbred mice.

Impaired breeding performance of aged female mice was associated with reduced numbers of ovulations and increased mortality of embryos. The amounts of progesterone in the sera, corpora lutea and uterine flushings of these animals were similar to those of young animals when measured by radioimmunoassay.

The uptake of [3H] glucosamine-labelled glycoconjugates into the perivitelline space of preimplantation mouse embryos.

Autoradiography has been used to follow the synthesis and migration of labelled glycoconjugates into fertilized and unfertilized mouse eggs. Adult female mice were paired individually with males and injected with 100 microCi [3H] glucosamine, either when they were paired with males or at the time a vaginal plug was first detected. The mice were killed at intervals after the injection of label and 5-microns and semi-thin sections of the oviducts were processed for autoradiography. Labelled glycoconjugates passed rapidly into the perivitelline space of fertilized and unfertilized mouse eggs. There was a positive correlation between the density of label within the zona pellucida and the perivitelline space. Labelled glycoconjugates were maintained within the perivitelline space of many developing embryos for at least 48 h despite very low levels of label within the oviduct by this time. Other 2-cell embryos were only lightly labelled. It is suggested that labelled glycoconjugates may be derived from secretions of the cumulus cells which surround the egg at ovulation rather than from oviductal secretions.

An autoradiographic study using [3H]glucosamine of gonadotrophin regulation of proteoglycan and glycoprotein synthesis in developing mouse follicles.

Autoradiography of serial sections of ovaries of immature mice was used, after an injection of [3H]glucosamine, to follow the migration of newly synthesized macromolecules into preantral follicles during the period of treatment with PMSG and hCG. [3H]Glucosamine was injected at the same time as the PMSG or 2-h before the time of autopsy. PMSG stimulated a modest uptake of [3H]glucosamine into the zona pellucida of preantral follicles. However, the in-vivo synthesis of labelled macromolecules increased substantially during the period of hCG stimulation, especially in those mice in which the label was injected at the same time as the PMSG. After both short and longer term exposure to [3H]glucosamine, the maximum uptake of label in preantral follicles occurred 4-8 h after the injection of hCG, indicating that hCG rather than PMSG probably exerts the greatest control over the uptake and incorporation of [3H]glucosamine into the zona pellucida and oocyte of preantral follicles. It is suggested that [3H]glucosamine is largely incorporated into non-sulphated glycosaminoglycans.

The secretions of the cumulus-oocyte complex in relation to fertilization and early mouse embryonic development: a histochemical study.

A study has been made of the histochemical composition of the murine cumulus-oocyte complex and zona pellucida following treatment of immature females with exogenous gonadotrophins. Selected developmental stages were studied in detail, namely the ovulated and unfertilized egg, the fertilized oocyte and the preimplantation embryo. In addition, the histochemical features observed in normal fertilized embryos have been compared with those of haploid and diploid parthenogenetic embryos at comparable stages following activation. Shortly after fertilization, glycosaminoglycans, which form a major component of the extracellular matrix surrounding the cumulus cells, become incorporated into the zona pellucida of the fertilized egg. In oocytes with few or no attendant cumulus cells, there appeared to be a diminished uptake of glycosaminoglycans and a reduced intensity of the zona staining reaction to Alcian Blue. In these oocytes, uptake of glycosaminoglycans appeared to be from the secretions lining the oviduct. There was little incorporation of the glycosaminoglycans from the extra-cellular matrix of the surrounding cumulus cells into the zona pellucida in unfertilized or parthenogenetic eggs despite the activation stimulus. After fertilization or activation, the zona pellucida became increasingly PAS-positive. Enzymic studies clearly indicate that the composition of the zona pellucida of the early embryo is histochemically different from the zona that surrounds the oocyte in the preovulatory follicle. These findings are discussed in relation to the decreased viability of embryos from oocytes which have been ovulated.

A brief illustrated guide to the ultrastructure of Plasmodium falciparum asexual blood stages.

Interpretation of the new information arising from the Plasmodium falciparum Genome Project requires a good working knowledge of the ultrastructure of the parasite; however many aspects of the morphology of this species remain obscure. Lawrence Bannister, John Hopkins and colleagues here give an illustrated overview of the three-dimensional (3-D) organization of the merozoite, ring, trophozoite and schizont stages of the parasite, based on available data that include 3-D reconstruc-tion from serial electron microscope sections. The review describes the chief organelles present in these stages, emphasizing the continuity of structure in addition to specialized, stage-specific features developed during the asexual erythrocytic cycle.

Microtubules in Plasmodium falciparum merozoites and their importance for invasion of erythrocytes.

Plasmodium falciparum merozoites have an array of 2-3 subpellicular microtubules, designated f-MAST. We have previously shown that colchicine inhibits merozoite invasion of erythrocytes, indicating a microtubular involvement in this process. Colchicine inhibition of invasion was reduced by the Taxol-stabilization of merozoite microtubules prior to colchicine exposure. Immunofluorescence assays showed that the number and length of f-MASTs were reduced in colchicine-treated merozoites, confirming that microtubules were the target of colchicine inhibition. The dinitroaniline drugs, trifluralin and pendimethalin, were shown by immunofluorescence to depolymerize the f-MAST and both drugs were inhibitory in invasion assays. These results demonstrate that the integrity of the f-MAST is important for successful invasion. Fluorescence imaging demonstrated the alignment of mitochondria to f-MAST, suggesting that mitochondrial transport might be perturbed in merozoites with disorganized f-MAST. Depolymerizing mt in late-stage schizonts did not affect the allocation of mitochondria to merozoites.

Ultrastructure of rhoptry development in Plasmodium falciparum erythrocytic schizonts.

Prior to the separation of merozoites from the Plasmodium falciparum schizont, various stage-specific organelles are synthesized and assembled within each merozoite bud. The apical ends of the merozoites are initiated close to the ends of endomitotic spindles. At each of these sites, the nuclear membrane forms coated vesicles, and a single discoidal or cup-like Golgi cisterna appears. Reconstruction from serial sections indicates that this structure receives vesicles from the nuclear envelope and in turn gives off coated vesicles to generate the apical secretory organelles. Rhoptries first form as spheroidal structures and grow by progressive fusion of small vesicles around their margins. As each rhoptry develops, 2 distinctive regions separate within it, an apical reticular zone with electron-lucent areas separated by cords of granular material, and a more homogenously granular basal region. The apical part elongates into the duct, with evidence for further vesicular fusion at the duct apex. The rounded rhoptry base becomes progressively more densely packed to form a spheroidal mass, and compaction also occurs in the duct. Typically, one rhoptry matures before the other. Cryofractured rhoptry membranes show asymmetry in the sizes and numbers of intramembranous particles at the internally- and externally-directed fracture faces.

Inhibitory action of the anti-malarial compound atovaquone (566C80) against Plasmodium berghei ANKA in the mosquito, Anopheles stephensi.

The activity of atovaquone against Plasmodium berghei ANKA during sporogonic development has been examined. Anopheles stephensi mosquitoes were fed on gametocyte infected mice which had been treated 8 h previously with atovaquone or diluent alone. Mosquito midguts were examined for oocysts, and salivary gland infections were estimated using an ELISA for the circumsporozoite protein (CSP). The number of oocysts per midgut fell by at least 97% when mosquitoes were fed on mice dosed with 0.1-10 mg atovaquone/kg body weight. This was paralleled by a decrease in the prevalence of oocyst-infected mosquitoes from 70-90% in controls to 40% or 10% respectively. No oocysts were observed at a dose of 100 mg/kg. CSP ELISA results indicated that mosquitoes fed on atovaquone failed to produce sporozoites. Mosquitoes which fed on gametocytaemic, atovaquone-treated mice (0.1-100 mg/kg) did not transmit malaria to naive mice. These results demonstrate that atovaquone has a highly potent inhibitory activity against the mosquito stages of P. berghei.

Ultrastructural and histochemical changes in the murine zona pellucida during the final stages of oocyte maturation prior to ovulation.

The ultrastructural morphology of the mouse zona pellucida was studied in preovulatory follicles from the ovaries of immature mice treated with exogenous gonadotrophins. The ovaries were fixed in the presence of cetylpyridinium chloride, which precipitates carbohydrates, so that their loss during fixation and processing is substantially reduced. The semi-thin araldite sections obtained from osmicated material were viewed by conventional light microscopy, while the ultra-thin sections were examined by transmission electron microscopy. A parallel series of semi-thin sections of non-osmicated ovaries was deresined and subsequently stained with periodic acid Schiff (PAS). The morphological appearance of the zona pellucida in preovulatory oocytes changed during the final stages of oocyte maturation. A close correlation was observed between the ultrastructural appearance of the zona pellucida and that observed following PAS staining during the period studied. Real differences were observed in the location, density, and distribution of glycoconjugates within the zona pellucida during the final stages of oocyte maturation prior to and immediately following germinal vesicle breakdown. Similar changes in the zona were observed in adult females autopsied during proestrus and oestrus. The changes in the density and distribution of glycoconjugates are likely to have important consequences for fertilization by affecting sperm-zona binding and sperm-egg interactions.

The progesterone content of rabbit uterine flushings.

A detailed study has been made of the progesterone content of uterine flushings taken from rabbits of different endocrine states. A high content of progesterone was recovered from the uterine lumen of pregnant and pseudopregnant rabbits. The amount of progesterone recovered in the flushings was not simply dependent on the concentration in the plasma, because plasma progesterone concentrations rose before detection of progesterone in the flushings and remained high after uterine progesterone content had fallen. Progesterone did not appear in the uterine fluid unless uterine protein was present. This was particularly evident in rabbits treated with progesterone in which, despite abnormally high plasma concentrations, little progesterone was found in uterine fluid until the protein content increased. After treatment of rabbits with oestrogen at the time of ovulation, uterine progesterone was present in higher amounts concomitant with an elevation of protein content although the peak values of progesterone and protein were delayed by 2--3 days. Plasma progesterone concentrations of about 5 ng/ml were necessary before progesterone appeared in the uterine lumen.