Eggs forever?

A group of scientists from Harvard Medical School (Johnson et al., 2004) claims to have "established the existence of proliferative germ cells that sustain oocyte and follicle production in the postnatal mammalian ovary," expressing no doubts about their methods, results and conclusion. Johnson et al. based their conclusions of oocyte and follicular renewal from existing germline stem cells (GSC) in the postnatal mouse ovary on three types of observations: (1) A claimed discordance in follicle loss versus follicle atresia in the neonatal period and in the following pubertal and adult period; (2) immunohistochemical detection of proliferating GSC with meiotic capacity using combined markers for meiosis, germline, and mitosis; and (3) neo-folliculogenesis in ovarian chimeric grafting experiments with adult mice. Oogenesis is the process that transforms the proliferative oogonium into an oocyte through meiosis, followed by folliculogenesis and follicular and oocyte maturation. The most crucial part in producing a functional oocyte is firstly, initiation and completion of the first meiotic prophase, and secondly, enclosure of the resulting diplotene oocyte in a follicle. Neither of these two events has been shown to take place in Johnson et al.'s study of the postnatal mouse ovary. We hereby address the observations underpinning their hypothesis and conclude that it is premature to replace the paradigm that adult mammalian neo-oogenesis/folliculogenesis does not take place.     

Identification of DNA Polymerase γ in Eggs of a Teleost Fish (Loach)

DNA polymerase found in an extract from eggs of the teleost fish Misgurnus fossilis (loach) has been identified as an enzyme of the type. The enzyme was purified 4000- to 5000-fold from the extract by liquid chromatography. The DNA polymerase activity was sensitive to the inhibiting action of aphidicolin but resistant to N2-(p-n-butylphenyl)-2´- deoxyguanosine 5´-triphosphate (BuPdGTP). The enzyme activity correlates with the presence of a polypeptide with molecular mass of 120-130 kD that interacts specifically with polyclonal antibodies against calf thymus DNA polymerase as revealed by Western blotting and is presumably the catalytic subunit of the enzyme. The loach DNA polymerase possesses the 3´5´-exonuclease activity specific to single-stranded DNA and catalyzes distributive elongation of primers in primer–template complexes.     

Serious doubts over “Eggs forever?”

A recent commentary in this journal by Byskov et al. (2005) claims that, despite published results from numerous independent lines of investigation from our laboratory and others, there does not "exist any evidence for neo-folliculogenesis in the adult mammalian ovary." While we agree with Byskov et al. that our work represents a radical departure from the age-old dogma that mammalian females permanently lose the capacity for oocyte and follicle production during the perinatal period, careful examination of all of the available data leaves no doubt that adult female mammals retain the capacity for oogenesis and folliculogenesis. These findings do not change the fact that exhaustion of the oocyte pool occurs with advancing chronological age--a process responsible for driving the menopause in women--but rather question the basic mechanism underlying age-related ovarian failure. In this regard, studies of aging male mice have demonstrated that testicular atrophy is associated with a dramatic decline in the number, activity and quality of germline stem cells that maintain spermatogenesis during adulthood (Zhang et al., 2006). Therefore, to the contrary of the opinion of Byskov et al. that such a process would be "considered exceptional among stem cells," it is certainly reasonable to hypothesize that a similar deterioration of female germline stem cell function underlies the decline in oocyte quality and the onset of ovarian failure in aging females. Further, while we accept that a departure from conventional thinking can take years to gain widespread acceptance, we feel this resistance to change should not be construed as the sole means to voice opinions about the validity of our data or the maturity of our principal conclusion.     

How to Spot a Stranger's Egg? A Mimicry‐Specific Discordancy Effect in the Recognition of Parasitic Eggs

Egg discrimination by hosts is an antiparasitic defence to reject foreign eggs from the nest. Even when mimetic, the presence of brood parasitic egg(s) typically alters the overall similarity of all eggs in a clutch, producing a discordant clutch compared to more homogenous clutches of composed only of hosts’ own eggs. In multiple parasitism, the more foreign eggs are laid in the nest, the more heterogeneous the overall clutch appears. Perceptual filters and recognition templates cannot explain the known pattern of lower rejection rates of foreign eggs in multiple vs. single parasitism. We therefore assessed the role of clutch homogeneity and manipulated the colour of one or more eggs in the clutches of great reed warbler (Acrocephalus arundinaceus) hosts of common cuckoos (Cuculus canorus). Varying the colours of both the majority and the minority eggs caused predictable shifts in the rejection of the focal egg(s), and ejection rates of the minority egg colour consistently increased but only when it belonged to a more mimetic egg colour, relative to the less mimetic colour of majority eggs. The results imply that in addition to sensory filters, and template‐based cognitive decision rules, discordancy‐based rejection is affected by the overall clutch appearance and interacts with specific colours varying in the extent of mimicry, to contribute to the recognition decisions of hosts to reject parasitic eggs.     

Water Relations of Chelonian Eggs and Embryos: Is Wetter Better?

The exchange of water between a chelonian egg and its subterraneanenvironment is influenced by numerous factors, the most importantof which are (1) structure of the calcareous layer of the eggshell,(2) water potential and temperature in the nest, and (3) fractionof the eggshell that actually contacts soil in the nest cavity.Eggs with relatively porous shells tend to absorb large quantitiesof water from cool, moist environments and to lose large amountsof water to warm, dry ones. Net water-exchange by such eggsalso tends to be more favorable (= positive) when soil contactsthe entire eggshell than when a large fraction of the shellis exposed to air trapped inside the nest cavity. In contrast,eggs with relatively impermeable shells usually exchange onlysmall amounts of water with their environment, regardless ofthe physical conditions that prevail inside the nest. The patternof net water-exchange, together with size (and water content)of the freshly laid egg, determines the amount of water thatis available to sustain the embryo. An embryo having accessto a relatively large reserve of water will consume more ofits yolk and grow to larger size before hatching than will anembryo having access to a smaller reserve of water. Large, well-hydratedhatchlings may survive better than small, dehydrated animalsduring the trek overland from nest to water. If so, a cooler,wetter nest will also be a better nest.     

Is Aboriginal Food Less Allergenic? Comparing IgE-Reactivity of Eggs from Modern and Ancient Chicken Breeds in a Cohort of Allergic Children

Background

Hen''s egg allergy ranks among the most frequent primary food allergies in children. We aimed to investigate sensitization profiles of egg allergic patients and compare in vitro IgE reactivities of eggs from ancient chicken breeds (Araucana and Maran) with those from conventional laying hen hybrids.

Methodology

Egg allergic children (n = 25) were subjected to skin prick test, double blind placebo controlled food challenge, and sensitization profiles to Gal d 1–5 were determined by allergen microarray. IgE binding and biological activity of eggs from different chicken breeds were investigated by immunoblot, ELISA, and mediator release assays.

Principal Findings

We found that Gal d 1 and Gal d 2 are generally major egg allergens, whereas Gal d 3–5 displayed high sensitization prevalence only in patients reacting to both, egg white and yolk. It seems that the onset of egg allergy is mediated by egg white allergens expanding to yolk sensitization in later stages of disease. Of note, egg white/yolk weight ratios were reduced in eggs from Auraucana and Maran chicken. As determined in IgE immunoblots and mass analysis, eggs from ancient chicken breeds did not differ in their protein composition. Similar IgE-binding was observed for all egg white preparations, while an elevated allergenicity was detected in egg yolk from Araucana chicken.

Conclusion/Significance

Our results on allergenicity and biological activity do not confirm the common assumption that aboriginal food might be less allergenic. Comprehensive diagnosis of egg allergy should distinguish between reactivity to hen''s egg white and yolk fractions to avoid unnecessary dietary restrictions to improve life quality of the allergic child and its family.     

Mortality of Herring Eggs on Different Algal Substrates (Furcellaria spp. and Cladophora spp.) in the Baltic Sea – An Experimental Study

In the Baltic Sea, herring (Clupea harengus membras) spawns in the littoral zone, where its eggs are attached to algae or vascular plants. Field studies indicate that egg mortality can be very high (up to 100%) in eggs that are attached to red algae (Rajasilta et al., 1989, 1993). Because high mortality can be due to allelochemical effects of the algae, we studied the mortality of herring eggs on different algal substrates experimentally. Four types of substrates were tested: fresh Cladophora and Furcellaria, and Furcellaria that had decomposed six days or 23 days. The incubation time in the experiments was 3 days and incubation temperature 12–13 ^oC (ca. 700–800 h-degrees). The results were in accordance with observations made in field studies and indicated significant differences among the substrate types. In eggs attached to fresh Cladophora, mortality was significantly lower (mean=2.8%; n=20) than in those attached to Furcellaria, independently of the treatment of the algae. The highest values of mortality (mean=14.4%; n=20) were found in eggs attached to Furcellaria that had decomposed over a six days’ period. This suggested that Furcellaria contain some chemical substances, which can cause mortality in herring embryos and the effect seems to be dependent on the state of decomposition of the algae.     

A Crystallin Fold in the Interleukin-4-inducing Principle of Schistosoma mansoni Eggs (IPSE/α-1) Mediates IgE Binding for Antigen-independent Basophil Activation

The IL-4-inducing principle from Schistosoma mansoni eggs (IPSE/α-1), the major secretory product of eggs from the parasitic worm S. mansoni, efficiently triggers basophils to release the immunomodulatory key cytokine interleukin-4. Activation by IPSE/α-1 requires the presence of IgE on the basophils, but the detailed molecular mechanism underlying activation is unknown. NMR and crystallographic analysis of IPSEΔNLS, a monomeric IPSE/α-1 mutant, revealed that IPSE/α-1 is a new member of the βγ-crystallin superfamily. We demonstrate that this molecule is a general immunoglobulin-binding factor with highest affinity for IgE. NMR binding studies of IPSEΔNLS with the 180-kDa molecule IgE identified a large positively charged binding surface that includes a flexible loop, which is unique to the IPSE/α-1 crystallin fold. Mutational analysis of amino acids in the binding interface showed that residues contributing to IgE binding are important for IgE-dependent activation of basophils. As IPSE/α-1 is unable to cross-link IgE, we propose that this molecule, by taking advantage of its unique IgE-binding crystallin fold, activates basophils by a novel, cross-linking-independent mechanism.     

Do Nest Light Conditions Affect Rejection of Parasitic Eggs? A Test of the Light Environment Hypothesis

Discrimination of foreign eggs is one of the most studied aspects of host defences against avian brood parasites. Although many factors affecting host egg‐recognition processes have already been evaluated, only a few attempts have been made to test the importance of light conditions in microhabitats of host nests. Here, we examined whether the objectively measured nest light environment affects great reed warbler (Acrocephalus arundinaceus) responses towards real common cuckoo (Cuculus canorus) eggs. More specifically, we predicted that parasitic eggs will be rejected with a lower frequency from nests placed in darker conditions than those in lighter conditions. However, we found no effect of the ambient light on egg‐rejection behaviour alone, but the photosynthetically active radiation exhibited a positive interactive effect with chromatic contrast between cuckoo and host eggs. Most rejection events were accomplished when cuckoo eggs of poor mimicry were laid in well‐lit nests. Our study suggests that this phenomenon may have important implications for the evolution of egg mimicry and host egg discrimination. We encourage further testing of the light environment hypothesis in other host species breeding in variable nest microhabitats and light conditions.     

Hosts’ Responses to Parasitic Eggs: Which Cues Elicit Hosts’ Egg Discrimination?

Many hosts of the common cuckoo (Cuculus canorus) exhibit egg recognition, and reject parasitic eggs. How do hosts discriminate cuckoo eggs from their own? Hosts might be able to recognize their own eggs using the specific pigment pattern on the outer eggshell surface, which may serve as a cue for recognition. We tested if patterns of egg pigments (spottedness) contain this information by manipulating spot density of great reed warbler eggs (Acrocephalus arundinaceus). We also manipulated the colour of eggs when the original spot pattern remained the same. Spot density (approximately 15–75%) did not significantly affect rejection rate (8–20% rejection), but when spots fully covered the eggs, i.e. the eggshell was plain dark brown, rejection rate increased abruptly to 100%. A loglinear model revealed the significant influence of colour on rejection rates, although there was no interactive effect between spottedness and colour. Our results strongly support the differential use of egg markers in host’s egg discrimination, suggesting that spot density has limited importance compared to eggshell colour.     

Does the Small White Butterfly (Pieris rapae L.) Aggregate Eggs on Plants with Greater Gas Exchange Activity?

Few studies have investigated insect egg-laying preferences in relation to photosynthesis or transpiration of their host plants. It has been suggested that intravarietal preferences of the small white butterfly (Pieris rapae L.: Pieridae) include larger plants with characteristically higher transpiration rates. Interestingly this species, like many other Lepidoptera, may detect biogenic CO₂ gradients associated with photosynthesis. We studied egg-laying preferences in working farm environments examining relationships among host choice, plant gas exchange activity, and plant size. Females discriminated between plants in monocultures on the basis of height. A balance of pre- and post–alighting preferences resulted in plants of medium size receiving eggs. Post–alighting preferences led to plants, but not alighted leaves, with higher rates of photosynthesis supporting eggs. These findings do not support a mechanistic basis for the use of gas exchange activity during host selection but, for the first time, indicate the greater physiological activity of crop plants that ultimately received the eggs of a pest insect.     

Does the Number of Diapausing Eggs Laid on Bark Affect the Population Dynamics of the Spider Mite Panonychus mori?

We studied the relationship between number of diapausing eggs produced by the spider mite Panonychus mori and the subsequent population trend for a period of 3 years. Panonychus mori showed a single population density peak on its host plant moonseed, Cocculus trilobus. The position and height of this peak were correlated with the density of diapausing eggs around the moonseed leaf buds produced the winter before. In 1994 the density of diapausing eggs measured in February was 4.3/bud, which was 6–14 times higher than the density of diapausing eggs for the same period in 1995 (0.3/bud) and 1996 (0.7/bud). The subsequent population density peak in 1994 occurred in mid June and was about 2.5 times higher than the peaks in 1995 and 1996, which both occurred early September. Thus, the present study showed a positive correlation between the density of diapausing eggs on the host plant and the start and the extend of the population increase the next growing season. Predators associated with the spider mite population were phytoseiid mites, especially Amblyseius eharai was well synchronized with the spider mite density in 1994. Field observations revealed that P. mori produced diapausing eggs in response to short photoperiod in early October each year, which corresponded with the timing predicted by the critical photoperiod around 13 h at 18°C, as assessed in laboratory trials. Diapause ended by early April when egg hatchability attained about 50% and eggs took 9 days to hatch at 25°C and a 16L:8D photoperiod. Hatching in early April was twice faster than in late February.     

Does Help in Decision-Making in Biology Help in Decision-Making in Human Sciences and Conversely?

A link between biological and human sciences may be established, under the condition that we should admit the existence of reciprocal influences between them. The model for the regulation of agonistic antagonistic couples (MRAAC) is built from the study of biological systems and gives rise to specific types of control. This model can be helpful in decision processes in some human sciences such as management, economical and political strategies. The reason for such an opportunity lies in the fact that MRAAC is a general and phenomenological model able to incorporate the whole of the agonistic antagonistic systems. This type of regulation might be related to the concept of the viability of a system (yet also valid for human science systems) and to a functional and structural pattern which is the basis for agonistic antagonistic networks.     

Evidence of Different Ploidy Eggs Produced by Diploid F2 Hybrids of Carassius auratus (♀) × Cyprinus carpio (♂)

Based on the presence of three types of eggs with different diameters 0.13, 0.17 and 0.2 cm, we made two crosses: F₂ (♀) × diploid red crucian carp (♂), and F₂ (♀) × F₁₀ tetraploid (♂). The ploidy levels of the progeny of the two crosses were examined by chromosome counting and DNA content measurement by flow cytometer. In the offspring of the former cross, tetraploids, trip-loids, and diploid were obtained. In the progeny of the latter cross, tetraploids and triploids were observed. The production of the different ploidy level fish in the progeny of the two crosses provided a further evidence that F₂ might generate triploid, diploid and haploid eggs. The presence of the male tetraploid found in F₂ (♀) × diploid red crucian carp (♂) suggested that the genotype of XXXY probably existed in the tetraploid progeny. The gonadal structures of the tetraploids and triploids indicated that both female and male tetraploids were fertile and the triploids were sterile. We concluded that the formations of different ploidy level eggs from F₂ were contributed by endoreduplication and fusion of germ cells.     

Calcium signaling in pancreatic β-cells in health and in Type 2 diabetes

Changes in cytosolic free Ca²⁺ concentration ([Ca²⁺]_c) play a crucial role in the control of insulin secretion from the electrically excitable pancreatic β-cell. Secretion is controlled by the finely tuned balance between Ca²⁺ influx (mainly through voltage-dependent Ca²⁺ channels, but also through voltage-independent Ca²⁺ channels like store-operated channels) and efflux pathways. Changes in [Ca²⁺]_c directly affect [Ca²⁺] in various organelles including the endoplasmic reticulum (ER), mitochondria, the Golgi apparatus, secretory granules and lysosomes, as imaged using recombinant targeted probes. Because most of these organelles have specific Ca²⁺ influx and efflux pathways, they mutually influence free [Ca²⁺] in the others. In this article, we review the mechanisms of control of [Ca²⁺] in various compartments and particularly the cytosol, the endoplasmic reticulum ([Ca²⁺]_ER), acidic stores and mitochondrial matrix ([Ca²⁺]_mito), focusing chiefly on the most important physiological stimulus of β-cells, glucose. We also briefly review some alterations of β-cell Ca²⁺ homeostasis in Type 2 diabetes.     

Sex-associated difference in estrogen receptor β expression in N-methyl-N'-nitro-N-nitrosoguanidine-induced gastric cancers in rats

Epidemiologic studies indicate that the incidence of gastric cancer is higher in males than in females. Although the mechanisms mediating this difference are unclear, a role for estrogens has been proposed. We used Western blotting to evaluate the role of estrogen receptor (ER) subtypes ERα and ERβ and proliferating cell nuclear antigen (PCNA) in N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced gastric carcinogenesis in Wistar rats; ERα and ERβ mRNA levels also were analyzed by quantitative real-time RT-PCR analysis. The incidence of gastric cancer was significantly higher in male than female rats. In both sexes, ERα expression was similar in MNNG-treated cancerous and noncancerous tissues and normal gastric tissue. However, ERβ expression in MNNG-treated cancerous and noncancerous tissues was significantly lower in male rats and higher in female rats than that in normal gastric tissue; MNNG-induced cancerous tissue showed the highest ERβ expression. PCNA expression in MNNG-treated cancerous tissues was higher than that in noncancerous tissues, and was higher in male rats than female rats. Western blotting results were consistent with the mRNA changes determined by quantitative real-time RT-PCR. The present study provides evidence of a sex-associated difference in ERβ and PCNA expression in MNNG-induced gastric cancers in Wistar rats.     

Interindividual human variation in cisplatinum sensitivity, predictable in an in vitro assay?

Cisplatinum [cis-diamminedichloroplatinum(II)] is one of the most active antitumour agents and its effect is mainly due to the formation of cisplatinum-DNA crosslinks. Formation of cisplatinum-DNA intrastrand crosslinks in nucleated white blood cells of patients was measured, both in (pretreatment) samples exposed in vitro and in cells collected immediately after in vivo exposure to cisplatinum. Large interpatient variations were found. The in vitro results showed a linear correlation with the in vivo data (cc = 0.91). The in vitro measurements of crosslinks may allow prediction of response and avoidance of toxicity in individual patients.