Evolutionary aspects of primordial germ cell formation

Animal embryos can be classified into three types depending on the time when the adult body form is specified--after metamorphosis, progressively by addition of posterior segments, or as a single event early in development. Segregation of germ cells correlates with specification of adult body form. When the adult body form is specified late in development, e.g. after metamorphosis (molluscs, echinoderms, cirripedes, hemichordates, cephalochordates and ascidians), germ cells appear in the early adult and at the site where the gonads will develop. When the adult body form is specified progressively during development by the sequential addition of posterior segments (annelids, onychophorans and most arthropods) germ cells are segregated either before or during addition of segments, in close association with the growth zone. In nematodes, chaetognaths, collembolans, higher holometabolous insects and vertebrates, the adult body form is specified early in development and germ cells are typically segregated correspondingly early and in extraembryonic regions. Therefore, as a general conclusion, germ cells appear to be segregated in locations and/or at times that exclude them from the process of specification of adult body form. Germ plasm is restricted to embryos in which exclusion of germ cells is difficult because the embryo is small or the signal specifying adult body form is pervasive. A possible role for germ plasm is thus as additional protection for the cells from the processes specifying adult body form.

Determination of anterior endoderm in Xenopus embryos

Grafts of anterior endoderm from embryos at stage 28 or later developed according to their fate (i.e., anterior) when transplanted posteriorly. Conversely, grafts from earlier embryos developed according to their new location (i.e., posterior). However, endoderm grafted along with its mesodermal and ectodermal sheath retained its fate regardless of the stage of the donor. We conclude that anterior endoderm in Xenopus embryos is determined at about stage 25 under the influence of mesoderm.

Do depression symptoms predict early hypertension incidence in young adults in the CARDIA study? Coronary Artery Risk Development in Young Adults

BACKGROUND

Hypertension has been linked to several psychological factors, including depression, but the relation between hypertension incidence and depressive symptoms has not been adequately examined.

OBJECTIVE

To determine if depressive symptoms independently predict hypertension incidence.

DESIGN AND SETTING

A prospective, multicenter, epidemiological cohort of young adults (aged 23-35 years at study entry) from the general community without hypertension followed up for 5 years.

SUBJECTS

A sample of 3343 adults from 4 urban areas stratified for race (black and white) from the CARDIA (Coronary Artery Risk Development in Young Adults) study.

MAIN OUTCOME MEASURE

Hypertension incidence, which was defined as blood pressure higher than 160/95 mm Hg (assessed on a single occasion) or the use of prescribed antihypertensive medication.

RESULTS

Participants with high scores (> or = 16) on the Center for Epidemiological Studies Depression (CES-D) Scale were at significant risk for hypertension incidence compared with those with low CES-D scores (< or =7; odds ratio, 2.10; 95% confidence interval, 1.22-3.61) after adjustment for other hypertension risk factors (eg, age, resting systolic blood pressure at the 5-year examination, physical activity, daily alcohol use, parental history of hypertension, education, presence of diabetes mellitus or heart disease, sex, and race) in fixed logistic models. Those with intermediate depressive symptoms (CES-D scores 8-15) were also at significant risk (adjusted odds ratio, 1.78; 95% confidence interval, 1.06-2.98). These associations were significant in blacks alone but were not found in whites, who had a lower hypertension incidence (29 [2%] of 1806) than blacks (89 [6%] of 1537).

CONCLUSIONS

Depressive symptoms were predictive of later hypertension incidence in young adults, and young blacks with depressive symptoms were at high risk of developing hypertension.

Effects of retinoic acid on the endoderm in Xenopus embryos

When Xenopus embryos from mid-tailbud to early tadpole stages were exposed to retinoic acid (RA), the gut developed with an uncoiled, straight intestinal tube, morphogenesis of the liver and stomach was affected and intestinal epithelial cells developed without a brush border and alkaline phosphatase activity. However, the temporal and spatial expression pattern of X1Hbox 8, the only homeobox gene expressed in the endoderm was unaffected. In lateral plate mesodermal cells the expression of alpha-smooth muscle (SM) actin was delayed. A similar syndrome has been reported in a study of embryos lacking functional FGF receptors in which it was proposed that the uncoiled intestinal tube and the delayed differentiation of the intestinal muscle cells are causally related. Our results support this proposition and further suggest that mesenchymal-epithelial interactions concerned with regional specification of the endoderm may be impaired resulting in other defects in the gut.

A comparison of case-crossover and case-control designs in a study of risk factors for hemorrhagic fever with renal syndrome

The case-crossover design is a new method for studying acute effects of transient exposures, in which cases serve as their own controls. To assess the validity, strengths, and weaknesses of the design, we used both the case-crossover method and the traditional case-control method of multivariate analysis with data collected from 196 cases and 295 hospital controls to study risk factors for hemorrhagic fever with renal syndrome in Korean soldiers. Both case-control and case-crossover methods showed that living in primitive field conditions, exposure to dust, and exposure to rodents were risk factors; use of insecticides or insect repellents was protective. Odds ratios from the case-crossover method were generally somewhat higher for risk factors and lower for protective factors. The case-crossover technique has great potential as a powerful, cost-effective way to assess risk factors for conditions such as infectious diseases and injuries, while avoiding some of the bias and logistical problems of traditional study designs.

A hospital-based, case-control study of risk factors for hemorrhagic fever with renal syndrome in soldiers of the armed forces of the Republic of Korea

A hospital-based, case-control study was conducted to measure risk factors for hemorrhagic fever with renal syndrome in Korean soldiers. Between October 1989 and January 1992, 196 cases and 295 controls were admitted into the study. Information was collected on behavioral and environmental variables, and the data were analyzed by multiple logistic regression. The strongest risk factors were seeing Apodemus in the area (odds ratio [OR] = 4.9), living in a primitive dwelling such as a lean-to (OR = 3.9), and being exposed to dust (OR = 3.7). The most protective factors were living in barracks (OR = 0.3-0.5) and self-reported use of any insecticide or insect repellent (OR = 0.5).

Expression of beta-galactosidase from a hybrid promoter:operator element in Escherichia coli

A hybrid trpPO:lacO regulatory sequence was cloned upstream of a promoterless lacZ gene and recombined onto a lambda bacteriophage. Escherichia coli lysogens representing the four possible phenotypes for lacI and trpR were constructed and the synthesis of beta-galactosidase was assayed under various growth conditions. The results illustrated that both control elements could be efficiently and independently regulated by the addition or omission of appropriate accessory molecules.

Relocation and reorganization of germ plasm in Xenopus embryos after fertilization

In the unfertilized egg, germ plasm is widely distributed throughout the vegetal subcortex in small islets. Following fertilization or artificial activation, the location and organization changes, and by the 4- to 8-cell stage the germ plasm forms a small number of large patches overlying the vegetal pole. We distinguish three processes that produce these changes. The first of these is aggregation which involves the islets moving towards the vegetal pole to form large patches by coalescence. This phase requires microtubules but does not depend on cleavage or dynamic microfilaments. The second phase is ingression during which the patches of germ plasm move to the interior of the egg. The movement is due to a flow of cytoplasm from the vegetal pole internally and the cytoplasmic current does not require either microtubules or dynamic microfilaments. In the third phase, the germ plasm is trapped in the vegetal hemisphere by microtubular arrays—in normal development, the mitotic spindle.

Malaria: treatment efficacy of halofantrine (WR 171,669) in initial field trials in Thailand

Halofantrine (WR 171,669) hydrochloride was administered orally to 82 patients infected with Plasmodium falciparum malaria on the Thai-Kampuchean border between June 1982 and December 1983 in a randomized double-blind treatment trial which compared the efficacy of halofantrine with that of mefloquine. Halofantrine was curative with oral treatment on a single day in 65% of patients (13/20) who received 1000 mg followed 6 hours later by an additional 500 mg, and in 88% of patients (53/60) who received 500 mg every 6 hours for 3 doses. Mefloquine was curative in 88% of patients (22/25) given a single oral dose of 1000 mg and in 97% of patients (38/39) given a single oral dose of 1500 mg. The difference in cure rates between the 3-dose halofantrine regimen and either of the mefloquine regimens was not significant. The mean parasite clearance time for all regimens ranged from 75 to 84 hours. The mean fever clearance time for all four treatment groups was in the range 50-60 hours, with no significant differences between groups. Post-dosing side-effects in patients treated with halofantrine consisted of nausea, vomiting, abdominal pain and diarrhoea and were not significantly different from those treated with mefloquine. Halofantrine therefore appeared to be of comparable efficacy to mefloquine in the treatment of multidrug-resistant P. falciparum malaria.

The effect of egg rotation on the differentiation of primordial germ cells in Xenopus laevis

Eggs of X. laevis were rotated (sperm entrance point downwards) either through 90° (1×90 embryos) or 180° in two 90° steps (2×90 embryos) at approximately 25–30 min postfertilization after cooling to 13°C. The embryos were kept in their off-axis orientation and cooled until the early gastrula stage. Rotation resulted in relocation of egg constituents with slight changes in the distribution of outer cortical and subcortical components and major changes in inner constituents where the heavy yolk and cytoplasm appeared to reorient as a single coherent unit to maintain their relative positions with respect to gravity. Development of rotated embryos was such that regions of the egg which normally give rise to posterior structures instead developed into anterior structures and vice versa. Germ plasm was displaced in the vegetal-dorsal-animal direction (the direction of rotation) and was segregated into dorsal micromeres and intermediate zone cells in 2×90 embryos and dorsal macromeres and intermediate zone cells in 1×90 embryos. In consequence, at the gastrula stage, cells containing germ plasm were situated closer to the dorsal lip of the blastopore after rotation — in 2×90 gastrulas around and generally above the dorsal lip. Hence, in rotated embryos, the cells containing germ plasm were invaginated earlier during gastrulation and therefore were carried further anteriorly in the endoderm to a mean position anterior to the midpoint of the endoderm. The number of cells containing germ plasm in rotated embryos was not significantly different from that in controls at all stages up to and including tail bud (stage 25). However at stages 46, 48 and 49 the number of primordial germ cells was reduced in 1×90 embryos in one experiment of three and in 2×90 embryos in all experiments. We tested the hypothesis that the decreased number of primordial germ cells in the genital ridges was due to the inability of cells to migrate to the genital ridges from their ectopic location in the endoderm. When anterior endoderm was grafted into posterior endodermal regions the number of primordial germ cells increased slightly or not at all suggesting that the anterior displacement of the cells containing germ plasm was not the only factor responsible for the decreased number of primordial germ cells in rotated embryos. Other possible explanations are discussed.

The effect of egg rotation on the differentiation of primordial germ cells in Xenopus laevis

Eggs of X. laevis were rotated (sperm entrance point downwards) either through 90 degrees (1 X 90 embryos) or 180 degrees in two 90 degrees steps (2 X 90 embryos) at approximately 25-30 min postfertilization after cooling to 13 degrees C. The embryos were kept in their off-axis orientation and cooled until the early gastrula stage. Rotation resulted in relocation of egg constituents with slight changes in the distribution of outer cortical and subcortical components and major changes in inner constituents where the heavy yolk and cytoplasm appeared to reorient as a single coherent unit to maintain their relative positions with respect to gravity. Development of rotated embryos was such that regions of the egg which normally give rise to posterior structures instead developed into anterior structures and vice versa. Germ plasm was displaced in the vegetal-dorsal-animal direction (the direction of rotation) and was segregated into dorsal micromeres and intermediate zone cells in 2 X 90 embryos and dorsal macromeres and intermediate zone cells in 1 X 90 embryos. In consequence, at the gastrula stage, cells containing germ plasm were situated closer to the dorsal lip of the blastopore after rotation--in 2 X 90 gastrulas around and generally above the dorsal lip. Hence, in rotated embryos, the cells containing germ plasm were invaginated earlier during gastrulation and therefore were carried further anteriorly in the endoderm to a mean position anterior to the midpoint of the endoderm. The number of cells containing germ plasm in rotated embryos was not significantly different from that in controls at all stages up to and including tail bud (stage 25). However at stages 46, 48 and 49 the number of primordial germ cells was reduced in 1 X 90 embryos in one experiment of three and in 2 X 90 embryos in all experiments. We tested the hypothesis that the decreased number of primordial germ cells in the genital ridges was due to the inability of cells to migrate to the genital ridges from their ectopic location in the endoderm. When anterior endoderm was grafted into posterior endodermal regions the number of primordial germ cells increased slightly or not at all suggesting that the anterior displacement of the cells containing germ plasm was not the only factor responsible for the decreased number of primordial germ cells in rotated embryos. Other possible explanations are discussed.

A clinical trial of mefloquine in the treatment of Plasmodium vivax malaria

A clinical field trial was conducted to determine if mefloquine is effective in the treatment of malaria due to Plasmodium vivax. Forty patients with P. vivax malaria were treated with either mefloquine, chloroquine or chloroquine plus primaquine and followed for 28 days. All patients responded rapidly and were cured. There were no significant side effects.

Treatment of an acute case of Plasmodium malariae malaria with mefloquine

Mefloquine, a new antimalarial which has been effective in curing malaria due to Plasmodium falciparum and P. vivax, was used for the first time in a patient infected with P. malariae. Treatment was successful, and the relatively long parasite clearance time and fever clearance time were probably characteristic of P. malariae rather than true drug resistance.

A comparative trial of Mefloquine and Fansidar in the treatment of falciparum malaria: failure of Fansidar

Falciparum malaria in 104 Thai patients was treated with either Mefloquine or Fansidar and patients were examined for parasitaemia for the next 28 days. All but one of the 40 patients treated with Mefloquine were cured, but the cure rates for Fansidar were only 9 . 1% for the two-tablet regimen and 19 . 4% for the three-tablet regimen. Most failures were classified as RII. Serum sulpha levels indicated that the Fansidar was being absorbed. Immediate steps should be taken to eliminate this focus of resistance and to protect against further resistance to Fansidar by using it in combination with another effective anti-malarial and by vigorous vector control measures.

Effect of calcium and fatty acids on the isolation of stallion spermatozoa in BSA

Fifty ejaculates, ten from each of 5 mature stallions, were utilized to study the effects of calcium and fatty acids on equine spermatozoa which were isolated in 3% Bovine Serum Albumin (BSA). The ejaculates were evaluated for percent motile spermatozoa, rate of forward movement, debris, primary abnormalities and secondary abnormalities. The isolation procedure consisted of layering 2 ml of diluted semen (100 x 10(6) spermatozoa/ml) over 6 ml of 3% BSA in 13 x 125 mm columns in a water bath (37 degrees C). After 30 min., the top semen layer and upper half of the BSA layer were withdrawn from all columns and the lower half of the BSA was re-evaluated. A 2 x 2 factorial arrangement of treatments was utilized with either the inclusion or omission of calcium or fatty acids in the BSA isolation media. The percent motile spermatozoa and rate of forward movement were increased (P<.01) when fatty acids were included in the isolation media but decreased (P<.01) when they were omitted. The highest percent motile spermatozoa and rate of forward movement were observed with BSA in the presence of fatty acids and omission of calcium. The calcium by fatty acid interaction, stallion effect and stallion by treatment interaction were significant for percent motile spermatozoa. Less debris was observed in all samples of isolated spermatozoa when compared with the initial estimate. Isolation resulted in a reduction of (P<.01) the primary abnormalities. Also, fewer (P<.01) secondary abnormalities were observed after isolation in all treatments except 4 (-FA+Ca) than were found in the ejaculate sample.

Oropouche virus. II. Epidemiological observations during an epidemic in Santarém, Pará, Brazil in 1975

An epidemic of Oropouche fever occurred in Santarém, Pará, Brazil in 1975. In the first survey for Oropouche antibodies involving a random sample of an entire city, infection rates varied from 0-44%, depending on the specific area within the city. Women had higher infection rates than men, but this difference was statistically significant only for persons older than 10 years of age. An analysis of school data showed that pupils in the evening classes had a greater increase in absenteeism during the epidemic period than those attending morning or afternoon classes. These data are compatible with the concept that Culicoides paraensis rather than Culex pipiens quinquefasciatus is the main vector of Oropouche virus in Brazil.

Oropouche virus. III. Entomological observations from three epidemics in Pará, Brazil, 1975

Urban epidemics of Oropouche (ORO) fever in three municipalities in Pará, Brazil were studied in 1975. Culicoides paraensis (Goeldi) were collected during each of the epidemics and there was a positive correlation, by study areas within the city of Santarém, between human seropositivity to ORO virus and population densities of C. paraensis and Culex quinquefasciatus Say. The best numerical correlation was with populations of C. paraensis. The relative absence of other species in the areas of high disease attack rates was further evidence C. paraensis were the probable vectors of ORO virus. These biting midges were found to bite readily inside of houses, with an indoor/outdoor ratio of 29%, and were most active around 1700-1800 hours. Other biological observations on C. paraensis are presented.

Cell specialization in the epithelium of the small intestine of feeding Xenopus laevis tadpoles

The intestinal epithelium of feeding Xenopus laevis tadpoles was studied using light microscope, electron microscope and autoradiographic techniques. The wall of the small intestine differs from that of most other vertebrates studied in that it lacks villous-like folds. A single prominent longitudinal fold, the typhlosole, forms about stage 49, and a series of shallow longitudinal epithelial pleats is also present in some animals. The morphology of the epithelial cells indicates that there are no differences between the cells in their degree of specialization. Three epithelial cell types were recognized: principal cells, gland cells and endocrine cells, making up about 65%, 15% and 1%, respectively, of all cells present, while approximately 20% of the cells in the epithelium are lymphocytes, 1% appear to be discharged gland cells, and 2% degenerating cells. No Paneth, caveolated or undifferentiated cells were identified. The findings are discussed in relation to other studies on cell proliferation and on nuclear transplantation.

Cell specialization in the small intestinal epithelium of adult Xenopus laevis: functional aspects

The functional activity of the epithelial cells of the intestinal folds of Xenopus was analysed histochemically. There is a gradient of increasing absorptive, digestive and secretory activity from the trough regions to the crests of the longitudinal folds. The differences in functional activity correspond to differences in structural complexity, and confirm the existence of a more specialized population of cells at the fold crests and a less specialized population at the fold troughs, analogous to mammalian villous and crypt cells respectively.

Cell specialization in the small intestinal epithelium of adult Xenopus laevis: structural aspects

The structure, cellular composition and organization of the small intestinal epithelium of adult Xenopus laevis are described. The mucosa is thrown into a system of longitudinal folds and is composed mainly of columnar cells and goblet cells. Leucocytes comprise about 28% of the mucosal cells. The degree of structural specialization of columnar cells varies according to their position in the folds. Cells at the crest of the folds display the greastest degree of specialization, evidenced by the degree of development of their inter- and intracellular membrane systems. Cells in the trough regions between the folds are much less specialized. These cell types are structurally analogous to mammalian villous and crypt cells respectively, although they are not segregated to the same degree.

Events in the germ cell lineage after entry of the primordial germ cells into the genital ridges in normal and u.v.-irradiated Xenopus laevis

Approximately 20–25 primordial germ cells leave the endoderm between stages 38–41 and localize in the dorsal root of the mesentery by stage 43/44. At this time all the cells contain large quantities of yolk which is gradually resorbed. The cells begin dividing between stages 48–52. The number and size of the germ cells were measured in tadpoles between stages 48–54 of development. The results indicate that in females the germ cells divide more often than in males. In both sexes the mitoses are grossly unequal, leading to the formation of a new generation of germ cells which are considerably smaller (one-tenth to one-fifth) than the size of the primordial germ cells at stage 48. The germ cells in male tadpoles at stage 54 are larger than in female tadpoles at the same stage. In tadpoles which developed from eggs irradiated in the vegetal hemisphere with u.v. light at the 2- to 4-cell-stage, primordial germ cells migrate into the genital ridges much later (stage 46–48) than in unirradiated embryos. They also differ morphologically from germ cells in control animals at this stage in that they are approximately one-tenth the size, lacking yolk in the cytoplasm and have a more highly lobed nucleus. Comparison of the results in unirradiated and irradiated animals suggests that the germ cell lineage is composed of a series of ordered, predictable events, and serious disruption of one of the events deranges later events.

Nuclear transplantation from intestinal epithelial cells of early and late Xenopus laevis tadpoles

The aim of these experiments was to test whether the developmental potential of nuclei from intestinal epithelial cells of Xenopus laevis tadpoles declined during the life of the functional larval gut. The results of transplantation of nuclei from three different stages of development were compared: stages 46–48, when feeding begins and while yolk is still present but before the formation of the typhlosole; stage 57, just prior to the onset of metamorphic reorganization; and stage 54, an intermediate stage. The results showed that there was no change in developmental potential of these nuclei during the life of the larval gut, thereby disproving the hypothesis that nuclear transplants from intestinal epithelial cells of early tadpoles of X. laevis will support extensive development because the cells are not fully functional. However, nuclei from the intestinal epithelial cells were less able to support development than blastula nuclei. It was concluded therefore, that the developmental potential of the gut nuclei is restricted relative to that of the blastula nuclei, but that these restrictions are reversed in a small proportion of cases.

Nuclear transplantation from intestinal epithelial cells of early and late Xenopus laevis tadpoles

The aim of these experiments was to test whether the developmental potential of nuclei from intestinal epithelial cells of Xenopus laevis tadpoles declined during the life of the functional larval gut. The results of transplantation of nuclei from three different stages of development were compared: stages 46-48, when feeding begins and while yolk is still present but before the formation of the typhlosole; stage 57, just prior to the onset of metamorphic reorganization; and stage 54, an intermediate stage. The results showed that there was no change in developmental potential of these nuclei during the life of the larval gut, thereby disproving the hypothesis that nuclear transplants from intestinal epithelial cells of early tadpoles of X. laevis will support extensive development because the cells are not fully functional. However, nuclei from the intestinal epithelial cells were less able to support development than blastula nuclei. It was concluded therefore, that the developmental potential of the gut nuclei is restricted relative to that of the blastula nuclei, but that these restrictions are reversed in a small proportion of cases.

An autoradiographic analysis of nucleic acid synthesis in the presumptive primordial germ cells of Xenopus laevis

Microinjection of [3H]thymidine into Xenopus laevis embryos between late blastula (stage 10) and early tadpole (stage 44) showed that the presumptive primordial germ cells synthesise DNA between stages 10–33. The percentage of labelled cells was highest between stages 10 and 16, declined sharply between stages 22 and 26 and rose again between stages 26 and 33. The fluctuations in the labelling patterns together with increase in the number of presumptive primordial germ cells and direct observation of germ cells in mitosis suggested that the germ cells divide three times between stages 10 and 44. The first divisions probably take place during gastrulation (stages 10–12), the second relatively synchronously at about stages 22–24 and the third series again relatively synchronously about stages 37–39. This period of proliferative activity is distinguishable on the one hand from the cleavage divisions in which the number of germ cells does not increase and on the other hand from the next proliferative phase by a period of mitotic inactivity. Microinjection of [3H]uridine showed that the presumptive primordial germ cells synthesize RNA only in mid-gastrula to early tail-bud-stage embryos. There is no obvious simple causal relationship between RNA synthesis and the movement of the germ plasm to the nucleus, or with division of the germ cells or with their migration out of the endoderm.

An autoradiographic analysis of nucleic acid synthesis in the presumptive primordial germ cells of Xenopus laevis

Microinjection of [3H]thymidine into Xenopus laevis embryos between late blastula (stage 10) and early tadpole (stage 44) showed that the presumptive primordial germ cells synthesis DNA between stages 10-33. The percentage of labelled cells was highest between stages 10 and 16, declined sharply between stages 22 and 26 and rose again between stages 26 and 33. The fluctuations in the labelling patterns together with increase in the number of presumptive primordial germ cells and direct observation of germ cells in mitosis suggested that the germ cells divide three times between stages 10 and 44. The first divisions probably take place during gastrulation (stages 10-12), the second relatively synchronously at about stages 22-24 and the third series again relatively synchronously about stages 37-39. This period of proliferative activity is distinguishable on the one hand from the cleavage divisions in which the number of germ cells does not increase and on the other hand from the next proliferative phase by a period of mitotic inactivity. Microinjection of [3H]uridine showed that the presumptive primordial germ cells synthesize RNA only in mid-gastrula to early tail-bud-stage embryos. There is no obvious simple causal relationship between RNA synthesis and the movement of the germ plasm to the nucleus, or with division of the germ cells or with their migration out of the endoderm.

Protein synthesis and germ plasm in cleavage embryos of Xenopus laevis

(3H) leucine was injected into unfertilized eggs, fertilized eggs, and Stage 2-12 embryos of X. laevis. Incorporation of the leucine into protein by blastomeres containing germ plasm was studied autoradiographically. Eggs, both fertilized and unfertilized, actively synthesized protein, ad did embryos from Stage 2 onwards. Probably all blastomerers containing germ plasm were labelled. In embryos from Stages 4-12, the germ plasm itself was also labelled, and this result suggests that the germ plasm is metabolically active during cleavage.

Localization of adenosine o',5'-monophosphate in mouse epidermis by immunofluorescence

Adenosine 3',5'-monophosphate (cyclic AMP) has been localized in mouse epidermal cells using an immunofluorescent technique. Within 10 min following the intraperitoneal injection of isoproterenol or 30 hr following the topical application of croton oil in acetone, staining was clearly visible in the cytoplasm of the basal cells.

The effect of u.v. irradiation of the vegetal pole of Xenopus laevis eggs on the presumptive primordial germ cells

The initial effect of u.v. irradiation of the vegetal pole was to inhibit cleavage in the vegetal hemisphere although karyokinesis was not substantially affected. In this way a syncytium formed in the vegetal hemisphere which broke down into individual cells some time between morula and late blastula. The movement of the germ plasm from the peripheral cortical regions into the interior of the egg was not appreciably delayed although aggregation of the germ plasm did not take place until the individual presumptive primordial germ cells were formed when the syncytium broke down. The method of segregation of the germ plasm and formation of the presumptive primordial germ cells was therefore very different in irradiated embryos from the normal orderly processes which depend on normal cleavage patterns. After neurula, the number of presumptive primordial germ cells declined rapidly and at stage 43/44, when the genital ridges in normal embryos contain primordial germ cells, the genital ridges in irradiated embryos were sterile. These results raise the question whether derangement of the segregation of the presumptive primordial germ cells is solely responsible for the later abnormalities in the cell lineage or whether u.v. irradiation affects the germ plasm and therefore indirectly the germ cells.

The effect of u.v. irradiation of the vegetal pole of Xenopus laevis eggs on the presumptive primordial germ cells

The initial effect of u.v. irradiation of the vegetal pole was to inhibit cleavage in the vegetal hemisphere although karyokinesis was not substantially affected. In this way a syncytium formed in the vegetal hemisphere which broke down into individual cells some time between morula and late blastula. The movement of the germ plasm from the peripheral cortical regions into the interior of the egg was not appreciably delayed although aggregation of the germ plasm did not take place until the individual presumptive primordial germ cells were formed when the syncytium broke down. The method of segregation of the germ plasm and formation of the presumptive primordial germ cells was therefore very different in irradiated embryos from the normal orderly processes which depend on normal cleavage patterns. After neurula, the number of presumptive primordial germ cells declined rapidly and at stage 43/44, when the genital ridges in normal embryos contain primordial germ cells, the genital ridges in irradiated embryos were sterile. These results raise the question whether derangement of the segregation of the presumptive primordial germ cells is solely responsible for the later abnormalities in the cell lineage or whether u.v. irradiation affects the germ plasm and therefore indirectly the germ cells.

Effect of UV on cleavage of Xenopus laevis

UV irradiation of the vegetal pole of stage 2 X. laevis embryos with doses of 6000-18000 ergs/mm-2 delayed or inhibited cytokinesis in the vegetal hemisphere. Nuclear division continued so that a syncytium was formed, the size and persistence of which depended on the dose. Embryos which received a low UV dose were subsequently able to recover whereas embryos receiving a high dose were unable to gastrulate successfully. The implications for investigations into the role of cytoplasmic determinants are discussed.

Mitosis in presumptive primordial germ cells in post-blastula embryos of Xenopus laevis

In X. laevis embryos injected with (3-H) thymidine between early gastrula and late neurula, the presumptive primordial germ cell nuclei were labelled and some were observed in mitosis, confirming that division occurs throughout this developmental period. In all labelled and mitotic cells, the germ plasm adjoined the nucleus, an observation which invalidates the hypothesis that germ plasm inhibits mitosis in presumptive primordial germ cells after gastrula. In embryos which had been irradiated with UV at the vegetal pole at the 2-cell stage, the presumptive primordial germ cells also incorporated (3-H) thymidine and divided during the same developmental period.

Quantitative studies of germ plasm and germ during early embryogenesis of Xenopus laevis

The germ plasm in the egg is partitioned between the first four blastomeres by the first two cleavage planes. Although the blastomeres divide 10–11 times through the rest of cleavage, as shown by reduction in their size, the number of presumptive primordial germ cells (p.p. germ cells) does not increase significantly. During and as a result of the formation of the first two cleavage planes, the germ plasm aggregates together and moves towards and along the cleavage furrows. At subsequent mitoses, the germ plasm is localized at one of the poles of the spindle and hence is segregated to only one of the daughter cells, thus explaining how mitosis occurs without increase in the number of cells with germ plasm. Early in gastrulation, the germ plasm moves to a perinuclear position, therefore ensuring that as mitosis continues, both daughter cells receive germ plasm and the number of p.p. germ cells increases. Direct counts of the number of p.p. germ cells and measurements of their volume suggest that they divide twice between early gastrula and the stage at which they leave the endoderm. The p.p. germ cells behave similarly to the adjacent endodermal cells until they begin to migrate to the gonad, an event which may represent the first overt signs of differentiation. Measurements of the volume of germ plasm suggest that there is no change through cleavage. The general conclusion is drawn that during cleavage, the morphogenetic determinant germ plasm is segregated to a few cells by the normal processes of cleavage and that subsequently these cells undergo a small number of cloning divisions which are contemporaneous with the first signs of differentiation.

Quantitative studies of germ plasm and germ cells during early embryogenesis of Xenopus laevis

The germ plasm in the egg is paritioned between the first four blastomeres by the first two cleavage planes. Although the blastomeres divide 10-11 times through the rest of cleavage, as shown by reduction in their size, the number of presumptive primordial germ cells (p.p. germ cells) does not increase significantly. During and as a result of the formation of the first two cleavage planes, the germ plasm aggregates together and moves towards and along the cleavage furrows. At subsequent mitoses, the germ plasm is localized at one of the poles of the spindle and hence is segregated to only one of the daughter cells, thus explaining how mitosis occurs without increase in the number of cells with germ plasm. Early in gastrulation, the germ plasm moves to a perinuclear position, therefore ensuring that as mitosis continues, both daughter cells receive germ plasm and the number of p.p. germ cells increases. Direct counts of the number of p.p. germ cells and measurements of their volume suggest that they divide twice between early gastrula and the stage at which they leave the endoderm. The p.p. germ cells behave similarly to the adjacent endodermal cells until they begin to migrate to the gonad, an event which may represent the first overt signs of differentiation. Measurements of the volume of germ plasm suggest that there is no change through cleavage. The general conclusion is drawn that during cleavage, the morphogenetic determinant germ plasm is segregated to a few cells by the normal processes of cleavage and that subsequently these cells undergo a small number of cloning divisions which are contemporaneous with the first signs of differentiation.

An ultrastructural study of germ plasm in spermatogenesis of Xenopus lœvis

Spermatogonia and primary diplotene and zygotene spermatocytes contain an electrondense, finely granular substance which is usually closely associated with mitochondria; small patches of this substance also occur close to the nuclear membrane, often in the nuclear pores, and within the nucleus of primary spermatogonia. The fine structure of this substance is very similar to the fine structure of germ plasm in other stages of development, and since an ontogenetic continuity with germ plasm can be demonstrated, it was concluded that this substance is also germ plasm. The substance disappears about pachytene, earlier than in oogenesis where it persists until mid-diplotene, a difference which may be due to the fact that the oocyte stores large quantities of germ plasm in its cortex for the next generation of primordial germ cells. If the presence of the substance in the nuclear pores and within the nucleus is an indicator of synthesis of germ plasm, then synthesis stops in the secondary spermatogonium, which correlates with the subsequent absence of germ plasm from the pachytene spermatocyte stages. It is suggested that the function of the germ plasm in specifying germ line cells is carried out between the gastrula stage and the beginning of meiosis. The three events which take place during this period are (i) the migration of the presumptive primordial germ cells from the endoderm to the genital ridges, (ii) mitosis of the primordial germ cells and subsequently of the oogonia and spermatogonia in the developing gonads and (iii) preparations for meiosis. It is suggested that the mechanism of action of the germ plasm may be in the control of one or more of these processes. Other types of granular cytoplasmic deposits are also described, and their possible relationship to germ plasm discussed.