The chromatin accessibility dynamics during cell fate specifications in zebrafish early embryogenesis.

Chromatin accessibility plays a critical role in the regulation of cell fate decisions. Although gene expression changes have been extensively profiled at the single-cell level during early embryogenesis, the dynamics of chromatin accessibility at cis-regulatory elements remain poorly studied. Here, we used a plate-based single-cell ATAC-seq method to profile the chromatin accessibility dynamics of over 10 000 nuclei from zebrafish embryos. We investigated several important time points immediately after zygotic genome activation (ZGA), covering key developmental stages up to dome. The results revealed key chromatin signatures in the first cell fate specifications when cells start to differentiate into enveloping layer (EVL) and yolk syncytial layer (YSL) cells. Finally, we uncovered many potential cell-type specific enhancers and transcription factor motifs that are important for the cell fate specifications.

Maternal social environment shapes yolk testosterone allocation and embryonic neural gene expression in tree swallows.

Offspring from females breeding in competitive social environments are often exposed to more testosterone (T) during embryonic development, which can affect traits from growth to behavior in potentially adaptive ways. Despite the important role of maternally derived steroids in shaping offspring development, the molecular mechanisms driving these processes are currently unclear. Here, we use tree swallows (Tachycineta bicolor) to explore the effects of the maternal social environment on yolk T concentrations and genome-wide patterns of neural gene expression in embryos. We measured aggressive interactions among females breeding at variable densities and collected their eggs at two timepoints, including the day laid to measure yolk T concentrations and on embryonic day 11 to measure gene expression in whole brain samples. We found that females breeding in high-density sites experienced elevated rates of physical aggression and their eggs had higher yolk T concentrations. A differential gene expression and weighted gene co-expression network analysis indicated that embryos from high-density sites experienced an upregulation of genes involved in hormone, circulatory, and immune processes, and these gene expression patterns were correlated with yolk T levels and aggression. Genes implicated in neural development were additionally downregulated in embryos from high-density sites. These data highlight how early neurogenomic processes may be affected by the maternal social environment, giving rise to phenotypic plasticity in offspring.

Incubation as a driver of maternal effects: Temperature influences levels of yolk maternally derived 5α-dihydrotestosterone.

In birds, maternal hormones deposited into eggs in response to environmental stimuli can impact offspring phenotype. Although less studied, environmental conditions can also influence females' incubation behavior, which might play a role in regulating embryo exposure to maternal hormones through changes in incubation temperature that affect the activity of the enzymes responsible for converting testosterone (T) to 5α-dihydrotestosterone (DHT) or estradiol. Here, we tested the hypothesis that the initial T content of the yolk and incubation temperature determine exposure to T metabolites during early embryo development. In the Japanese quail (Coturnix japonica), we experimentally manipulated yolk T and incubation temperature (38° C versus 36° C) and analyzed DHT and estradiol titers on day four of incubation. We found that eggs with experimentally increased T and those incubated at 36° C showed higher DHT concentration in egg yolk (with no synergistic effect of the two treatments). Estradiol titers were not affected by T manipulation or incubation temperature. Our study suggests that incubation temperature influences DHT titers and may act as an understudied source of maternal influence on offspring phenotype.

Extraembryonic metabolism of corticosterone protects against effects of exposure.

When females experience stress during reproduction, developing embryos can be exposed to elevated levels of glucocorticoids, which can permanently affect offspring development, physiology, and behavior. However, the embryo can regulate exposure to glucocorticoids. In placental species, the placenta regulates embryonic exposure to maternal steroids via metabolism. In a comparable way, recent evidence has shown the extraembryonic membranes of avian species also regulate embryonic exposure to a number of maternal steroids deposited in the yolk via metabolism early in development. However, despite the known effects of embryonic exposure to glucocorticoids, it is not yet understood how glucocorticoids are metabolized early in development. To address this knowledge gap, we injected corticosterone into freshly laid chicken (Gallus gallus) eggs and identified corticosterone metabolites, located metabolomic enzyme transcript expression, tracked metabolomic enzyme transcript expression during the first six days of development, and determined the effect of corticosterone and metabolites on embryonic survival. We found that yolk corticosterone was metabolized before day four of development into two metabolites: 5ß-corticosterone and 20ß-corticosterone. The enzymes, AKR1D1 and CBR1 respectively, were expressed in the extraembryonic membranes. Expression was dynamic during early development, peaking on day two of development. Finally, we found that corticosterone exposure is lethal to the embryos, yet exposure to the metabolites is not, suggesting that metabolism protects the embryo. Ultimately, we show that the extraembryonic membranes of avian species actively regulate their endocrine environment very early in development.

The Effects of Different Doses of Canthaxanthin in the Diet of Laying Hens on Egg Quality, Physical Characteristics, Metabolic Mechanism, and Offspring Health.

Currently, there is a dearth of in-depth analysis and research on the impact of canthaxanthin on the production performance, egg quality, physical characteristics, and offspring health of laying hens. Furthermore, the metabolic mechanism of cantharidin in the body remains unclear. Therefore, to solve the above issues in detail, our study was conducted with a control group (C group), a low-dose canthaxanthin group (L group), and a high-dose canthaxanthin group (H group), each fed for a period of 40 days. Production performance was monitored during the experiment, in which L and H groups showed a significant increase in ADFI. Eggs were collected for quality analysis, revealing no significant differences in qualities except for yolk color (YC). The YC of the C group almost did not change, ranging from 6.08 to 6.20; however, the trend in YC change in other groups showed an initial intense increase, followed by a decrease, and eventually reached dynamic equilibrium. By detecting the content of canthaxanthin in the yolk, the YC change trend was found to be correlated with canthaxanthin levels in the yolk. The content of unsaturated fatty acid increased slightly in L and H groups. Following the incubation period, the physical characteristics and blood biochemical indices of chicks were evaluated. It was observed that the shank color of chicks in the L and H groups was significantly higher than that in the C group at birth. However, by the 35th day, there were no significant differences in shank color among the three groups. Further investigation into the metabolic mechanism involving canthaxanthin revealed that the substance underwent incomplete metabolism upon entering the body, resulting in its accumulation as well as metabolic by-product accumulation in the yolk. In summary, this study highlighted the importance of understanding canthaxanthin's role in production performance, egg quality, and offspring health, providing valuable insights for breeders to optimize feeding strategies.

Egg components and offspring survival vary with group size and laying order in a cooperative breeder.

Prenatal resource allocation to offspring can be influenced by maternal environment and offspring value, and affect offspring survival. An important pathway for flexible maternal allocation is via egg components such as nutrients and hormones. In cooperative breeders, females with helpers may increase resource allocation to eggs-'differential allocation'-or reduce it-'load-lightening'. Yet, helper effects on egg composition have been poorly studied. Moreover, it is unknown how helpers' presence modulates laying order effects on egg content and survival. Here, we investigated how maternal allocation varied with group size and laying order in the cooperatively breeding sociable weaver (Philetairus socius). We estimated interactive effects of helpers and laying order on allocation to egg mass, yolk nutrients-yolk mass, proteins, lipids, carotenoids, vitamin A and vitamin E-and hormones-testosterone, androstenedione, and corticosterone. Results concurred with the 'differential allocation' predictions. Females with more helpers produced later-laid eggs with heavier yolks and more lipids, and laid eggs overall richer in lipids. Proteins, antioxidants, and hormones were not found to vary with helper number. We then analyzed how helper number modulated laying order effects on survival. Females with more helpers did not specifically produce later-laid eggs with higher survival, but eggs laid by females with more helpers were overall more likely to fledge. These findings show that some egg components (yolk mass, lipids) can positively vary according to females' breeding group size, which may improve offspring fitness.

Maternal age generates phenotypic variation in Caenorhabditis elegans.

Genetically identical individuals that grow in the same environment often show substantial phenotypic variation within populations of organisms as diverse as bacteria, nematodes, rodents and humans. With some exceptions, the causes are poorly understood. Here we show that isogenic Caenorhabditis elegans nematodes vary in their size at hatching, speed of development, growth rate, starvation resistance, fecundity, and also in the rate of development of their germline relative to that of somatic tissues. We show that the primary cause of this variation is the age of an individual's mother, with the progeny of young mothers exhibiting several phenotypic impairments. We identify age-dependent changes in the maternal provisioning of the lipoprotein complex vitellogenin to embryos as the molecular mechanism that underlies the variation in multiple traits throughout the life of an animal. The production of sub-optimal progeny by young mothers may reflect a trade-off between the competing fitness traits of a short generation time and the survival and fecundity of the progeny.

Egg viability and egg mass underlie immune tradeoffs and differences between urban and rural lizard egg yolk physiology.

Urbanization can cause innumerable abiotic and biotic changes that have the potential to influence the ecology, behavior, and physiology of native resident organisms. Relative to their rural conspecifics, urban Side-blotched Lizard (Uta stansburiana) populations in southern Utah have lower survival prospects and maximize reproductive investment via producing larger eggs and larger clutch sizes. While egg size is an important predictor of offspring quality, physiological factors within the egg yolk are reflective of the maternal environment and can alter offspring traits, especially during energetically costly processes, such as reproduction or immunity. Therefore, maternal effects may represent an adaptive mechanism by which urban-dwelling species can persist within a variable landscape. In this study, we assess urban and rural differences in egg yolk bacterial killing ability (BKA), corticosterone (CORT), oxidative status (d-ROMs), and energy metabolites (free glycerol and triglycerides), and their association with female immune status and egg quality. Within a laboratory setting, we immune challenged urban lizards via lipopolysaccharide injection (LPS) to test whether physiological changes associated with immune system activity impacted egg yolk investment. We found urban females had higher mite loads than rural females, however mite burden was related to yolk BKA in rural eggs, but not urban eggs. While yolk BKA differed between urban and rural sites, egg mass and egg viability (fertilized vs. unfertilized) were strong predictors of yolk physiology and may imply tradeoffs exist between maintenance and reproduction. LPS treatment caused a decrease in egg yolk d-ROMs relative to the control treatments, supporting results from previous research. Finally, urban lizards laid a higher proportion of unfertilized eggs, which differed in egg yolk BKA, CORT, and triglycerides in comparison to fertilized eggs. Because rural lizards laid only viable eggs during this study, these results suggest that reduced egg viability is a potential cost of living in an urban environment. Furthermore, these results help us better understand potential downstream impacts of urbanization on offspring survival, fitness, and overall population health.

Embryonic heart rate is affected by yolk androgens and egg laying sequence, and correlates with embryonic tissue growth: A study in rock pigeons.

Maternal androgen exposure can have crucial effects on offspring development. Bird eggs are frequently used for studying these effects and virtually all research in this field has focused on post-hatching offspring traits. Yet, much of the yolk, in which the maternal hormones are deposited, is consumed during the embryonic phase. Here, we studied the effects of yolk androgens during this prenatal period. As there is evidence that androgens stimulate post-hatching traits such as increased growth, we measured heart rate throughout incubation as a proxy for prenatal metabolism. Rock pigeons (Columba livia) typically lay 2-egg clutches with yolk androgen levels in second-laid eggs being consistently higher than in first-laid eggs. We investigated whether embryonic heart rate was higher in second- than first-laid eggs. Additionally, we increased yolk androgen levels (testosterone and androstenedione) with the mean difference between those in first- and second-laid eggs, to investigate whether the effects of androgens are egg sequence dependent. As expected, embryonic heart rate predicted body embryo organ- and body mass, and body dimensions, with body mass being significantly higher in second- than first-laid eggs. Androgen treated first-laid eggs increased heart rate to that of second-laid control eggs only temporally, yet it had an overall positive effect on embryo body dimensions but not on tissue mass. Our findings indicate that embryos from different egg laying sequence differed in heart rate and prenatal development outcomes but this can only partially be explained by their difference in maternal androgen levels.

Effect of adding lavender oil to laying quail diets on performance, egg quality, oxidative status, and fatty acid profile.

This study aims to investigate the effects of lavender essential oil on performance, egg quality parameters in quails, malondialdehyde (MDA) in fresh and stored (28 days at +4°C) eggs, and individual and total fatty acids. To this end, 100 female quails (Coturnix coturnix Japonica) which were 5 weeks old with an average weight of 224 g were used. The study lasted 45 days, including 10 days of introduction and 35 days of study. Quails were fed ad libitum with four different treatments. Four groups were formed as control groups (0g lavender essential oil/kg feed), Lav125 (125mg lavender essential oil/kg feed), Lav250 (250mg lavender essential oil/kg feed), and Lav500 (500mg lavender essential oil/kg feed). There were five subgroups under each group and five quails in each subgroup. Feed consumption and egg weight parameters increased in Lav500 group compared to the control group (p<0.05). The highest egg yield compared to the control group was determined in Lav500 group (p>0.05), and the highest egg mass compared to the control group was determined in Lav125 group. The highest feed conversion ratio compared to the control group was in Lav250 group (p>0.05). In addition, egg white height and Haugh Unit (HU) compared to the control group were the highest in Lav500 group (p<0.05). The MDA concentration decreased in Lav125 and Lav250 group in fresh and in Lav500 group in stored eggs (at +4C for 28 days) compared to the control group (p<0.05). Omega 3 fatty acids in fresh and stored eggs were higher in lavender groups compared to the control group (p<0.05). However, the concentration of omega 9 (oleic acid) fatty acid decreased in the lavender groups compared to the control group (p<0.05). As a result, it was found that adding lavender essential oil to the diet leads to an increase in body weight, egg yield, egg mass, egg weight, egg white height, HU, omega 3 fatty acids, and a decrease in MDA concentration.

Effects of supplemental dried wild leek (Allium scorodoprasum L. subsp. rotundum) leaves on laying performance, egg quality characteristics, and oxidative stability in laying hens.

This study aimed to examine the effect of dietary supplementation of dried wild leek (Allium scorodoprasum L. subsp. rotundum) leaves on laying performance, egg traits, antioxidant status, and oxidative stability in laying hens. For this purpose, a total of 96 Lohmann White laying hens aged 22 weeks allocated into four treatment groups each containing 24 hens. Hens were fed a diet supplemented with 0 (control), 1 (WL1), 2 (WL2), and 3 (WL3) g/kg dried wild leek (DWL) leaves. During the 10-week trial, egg weight was increased and feed efficiency was improved with 2 and 3 g/kg DWL leaves. No significant differences were observed among groups for egg production, feed intake, internal and external egg quality characteristics, and egg yolk cholesterol concentration. Levels of malondialdehyde and total antioxidant-oxidant status of egg yolk were not affected from DWL supplementation. However, 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity was increased and oxidative stress index was decreased in egg yolk. Superoxide dismutase enzyme activity was increased in the group of WL3, and total antioxidant status levels were increased in the groups of WL2 and WL3 in serum. DWL supplementation reduced serum cholesterol concentration significantly. No marked changes were observed in other blood parameters. In conclusion, DWL is considered to be high antioxidant supplement due to having high antioxidant capacity and important bioactive compounds. Dietary supplementation of DWL leaves at 3 g/kg could be a viable and beneficial feed additive to improve egg weight and feed efficiency, increase DPPH radical scavenging activity in egg yolk and antioxidant status of hen. Therefore, the usage of DWL leaves in the laying hen diets will be beneficial for egg producers and poultry nutritionists to produce functional eggs having low cholesterol and high antioxidants.

Phosphoproteomic analysis of duck egg yolk provides novel insights into its characteristics and biofunctions.

BACKGROUND: Although the importance of phosphorylation in the function of proteins is known, investigation of the protein phosphorylation of duck egg yolk (DEY) is still very limited. This study aimed to conduct a detailed phosphoproteomic study of DEY using immobilized metal affinity chromatography and ultra-high liquid chromatography tandem mass spectrometry. RESULTS: A total of 253 phosphorylation sites assigned to 66 phosphoproteins were identified in DEY, of which VTG-1, VTG-2, and fibrinogen alpha chain were found to be the highly phosphorylated proteins in DEY. The biological functions of the identified phosphoproteins were illuminated through gene ontology analysis, which showed that they were mainly involved in binding, catalytic, immune response, and metabolic activity. S-X-E and S-X-S were found to be the most conserved serine motifs of phosphorylation in DEY. The comparison of DEY phosphoproteins with those of chicken egg yolk (CEY) revealed that differences mostly involved molecular functions and biological processes. The comparison also revealed a higher phosphorylation level in DEY proteins. CONCLUSION: The higher phosphorylation level in DEY proteins than that in CEY proteins are supposed to help enhance duck growth performance and biological activities (e.g. antibacterial and antioxidant ability) for better adapting the humid environment the duck lived. © 2021 Society of Chemical Industry.

Prenatal yolk corticosterone exposure promotes skeletal growth and induces oxidative imbalance in yellow-legged gull embryos.

Maternally derived hormones induce variation in offspring phenotype, with consequences that can carry over into post-natal life and even into adulthood. In birds, maternal egg corticosterone (CORT) is known to exert contrasting effects on offspring morphology, physiology and behaviour after hatching. However, information on the effects of CORT exposure on pre-hatching embryonic development is limited. We experimentally increased yolk CORT levels in yellow-legged gull (Larus michahellis) eggs, and assessed the effects on embryo pre-hatching development and oxidative status of brain and liver. CORT-supplemented embryos reached a larger skeletal size and liver mass compared with controls. Embryos from CORT-injected last-laid eggs showed decreased activity of the hepatic antioxidant enzymes superoxide dismutase and catalase, while intermediate-laid eggs showed increased levels of lipid peroxidation. However, elevated yolk CORT did not affect oxidative stress endpoints in the brain. Our results indicate that elevated yolk CORT levels affect prenatal embryo development by promoting skeletal growth, and induce laying sequence- and organ-specific oxidative imbalance, with potential adverse consequences during postnatal life, especially for late-hatched offspring.

Conodipine-P1-3, the First Phospholipases A2 Characterized from Injected Cone Snail Venom.

The phospholipase A2 (PLA2s) superfamily are ubiquitous small enzymes that catalyze the hydrolysis of phospholipids at the sn-2 ester bond. PLA2s in the venom of cone snails (conodipines, Cdpi) are composed of two chains termed as alpha and beta subunits. Conodipines are categorized within the group IX of PLA2s. Here we describe the purification and biochemical characterization of three conodipines (Cdpi-P1, -P2 and -P3) isolated from the injected venom of Conus purpurascens Using proteomics methods, we determined the full sequences of all three conodipines. Conodipine-P1-3 have conserved consensus catalytic domain residues, including the Asp/His dyad. Additionally, these enzymes are expressed as a mixture of proline hydroxylated isoforms. The activities of the native Conodipine-Ps were evaluated by conventional colorimetric and by MS-based methods, which provide the first detailed cone snail venom conodipine activity monitored by mass spectrometry. Conodipines can have medicinal applications such inhibition of cancer proliferation, bacterial and viral infections among others.

The influences of Tylosine and licorice dietary supplementation in terms of the productive performance, serum parameters, egg yolk lipid profile, antioxidant and immunity status of laying Japanese quail under heat stress condition.

By reducing feed consumption, animals suffering from heat stress prefer to reduce their heat output. Heat exposure has also contributed to major adverse effects on the productive and reproductive performance of quails. Therefore, this research was intended to estimate the preventive function of licorice as a safe feed additive against the negative effects caused by heat stress conditions on laying quail productivity. A total number of 180 Japanese quail birds (120 females and 60 males), nine-weeks old were divided into five groups. Each group contained 36 birds in four replicates (nine birds) with completely randomized design. The dietary treatments were a basal diet without supplementation as control (T1), basal diet + 100 mg Tylosine kg-1 diet (T2), (T3), (T4) and (T5) fed basal diet + 250, 500 and 1000 mg licorice kg-1 diet, in respect. The results indicated that dietary supplementation with different feed additives had no significant effects on egg-laying rate, egg number, average egg weight, egg mass and feed conversion ratio compared with control. Also, different treatments showed no significant variations on serum IgG, total protein, globulin, albumin, creatinine, ALT and TAC and caused significant (P ≤ 0.05) improvement in IgM, AST, ALP, uric acid and MDA concentrations as compared to the control. Results indicated that total serum lipids, triglycerides, total cholesterol and LDL concentrations were significantly decreased due to different feed additives. However, HDL concentrations and HDL/LDL ratios were markedly increased by the other treatments than the control group. In addition, yolk total lipids were significantly (P ≤ 0.001) decreased with increasing licorice root powder's dietary levels compared with the control group. Also, a significant (P ≤ 0.01) reduction in egg yolk cholesterol level was observed in the group fed with 500 mg licorice compared to other treatments. In conclusion, fortified laying quail diets with licorice powder could be a useful strategy to alleviate adverse effects induced by heat stress as alternative to antibiotics on laying Japanese quail.

Effect of consumption of whole egg and egg fractions on cardiovascular disease factors in adult rats.

BACKGROUND: While eggs are a low-cost source of protein, rich in macro- and micronutrients, the association of egg intake and cardiovascular disease (CVD) remains controversial. This study investigated the effect of egg consumption on CVD parameters. Eggs were boiled, separated into four fractions (whole egg, 50% yolk-reduced whole egg, egg yolk and egg white) and then freeze-dried. The different egg fractions or distilled water (control) were orally gavaged to adult male Wistar rats at 1 g kg-1 rat body weight, each day for 8 weeks, following which basal blood pressure, heart rate, complete blood cell count, blood biochemistry, body fat and liver cell lipid accumulation were determined. The vascular functions of isolated thoracic aorta were studied using classical pharmacological techniques. RESULTS: In comparison to the control group, none of the egg fractions affected body weight, food intake, plasma glucose or lipid profile. The yolk group experienced increased plasma alkaline phosphatase and creatinine levels, while egg white caused decreased plasma cholesterol and blood urea nitrogen. Whole egg and egg yolk increased blood pressure and mean hemoglobin concentration and the yolk increased liver lipid accumulation. Egg white decreased the white blood cell count and body fat lipids. No changes were found in basal heart rate or vascular functions in any of the groups. CONCLUSIONS: Consumption of whole egg or egg yolk at the dosage given caused hypertension, with impairment of liver and kidney functions following the intake of yolk alone. However, egg white is beneficial for the cardiovascular system as it decreased plasma cholesterol and body fat accumulation. © 2020 Society of Chemical Industry.

Effects of supplementation of dietary humate, probiotic, and their combination on performance, egg quality, and yolk fatty acid composition of laying hens.

This study was carried out to determine the effects of addition of humate, probiotic, and their combination into diets on performance, egg quality, and yolk fatty acid composition of hens during the second laying period. Lohmann LSL white layers (n = 192), 46 weeks of age, were randomly divided into 4 groups and fed with basal diet (control, C), 0.3% humate (H), 0.3% probiotic (P), 0.15% humate + 0.15% probiotic (HP) for 18 weeks. Feed consumption and egg production were determined daily, egg weight was measured biweekly, and body weights were recorded at the beginning and the end of the experiment. Also, 12 egg samples from each group were randomly collected to determine the egg quality every 30 days. Laying performance, yolk color, and fatty acid composition were significantly (P < 0.05 and P < 0.01) affected by addition of humate, probiotic, and their combination into diets of layers. The HP group had higher cracked egg yield and feed conversion ratio values than control and H and P groups. Except for egg yolk color, the other egg quality parameters such as shape index, shell strength, shell thickness, albumen index, yolk index, and Haught unit were not affected by treatment (P < 0.05 and P < 0.01). The egg yolks of treatment groups had less stearic acid than those of control group. In conclusion, supplementation of humate and probiotic into the diets of laying hens increased monounsaturated fatty acids in yolk and improved feed conversion ratio and egg yolk color.

Assessment of Embryonic Bioactivity through Changes in the Water Structure Using Near-Infrared Spectroscopy and Imaging.

We explored the influence of embryonic bioactivity on the water structure using near-infrared (NIR) spectroscopy and imaging. Four groups of Japanese medaka fish (Oryzias latipes) eggs were studied: (a) one group of eggs was activated by fertilization, and (b-d) three groups of eggs were not activated because embryogenesis was stopped or not started by (b) culturing under cold temperature, (c) instant freezing, or (d) lack of fertilization. The yolks of the activated eggs contained higher proportions of weakly hydrogen bonded water than those of nonactivated eggs. A possible factor responsible for the significant changes in the water structure was revealed to be a protein secondary structural change from an α-helix to a ß-sheet in the activated eggs. NIR images of the activated eggs successfully visualized the water structural variation in the yolk with a higher proportion of weak hydrogen bonds due to the activation of embryonic development. The embryogenic activity could be assessed through the water hydrogen bond network, which is affected by newly generated proteins with different secondary structures.

Vegetally localised Vrtn functions as a novel repressor to modulate bmp2b transcription during dorsoventral patterning in zebrafish.

The vegetal pole cytoplasm represents a crucial source of maternal dorsal determinants for patterning the dorsoventral axis of the early embryo. Removal of the vegetal yolk in the zebrafish fertilised egg before the completion of the first cleavage results in embryonic ventralisation, but removal of this part at the two-cell stage leads to embryonic dorsalisation. How this is achieved remains unknown. Here, we report a novel mode of maternal regulation of BMP signalling during dorsoventral patterning in zebrafish. We identify Vrtn as a novel vegetally localised maternal factor with dorsalising activity and rapid transport towards the animal pole region after fertilisation. Co-injection of vrtn mRNA with vegetal RNAs from different cleavage stages suggests the presence of putative vegetally localised Vrtn antagonists with slower animal pole transport. Thus, vegetal ablation at the two-cell stage could remove most of the Vrtn antagonists, and allows Vrtn to produce the dorsalising effect. Mechanistically, Vrtn binds a bmp2b regulatory sequence and acts as a repressor to inhibit its zygotic transcription. Analysis of maternal-zygotic vrtn mutants further shows that Vrtn is required to constrain excessive bmp2b expression in the margin. Our work unveils a novel maternal mechanism regulating zygotic BMP gradient in dorsoventral patterning.

Nuclear movement regulated by non-Smad Nodal signaling via JNK is associated with Smad signaling during zebrafish endoderm specification.

Asymmetric nuclear positioning is observed during animal development, but its regulation and significance in cell differentiation remain poorly understood. Using zebrafish blastulae, we provide evidence that nuclear movement towards the yolk syncytial layer, which comprises extraembryonic tissue, occurs in the first cells fated to differentiate into the endoderm. Nodal signaling is essential for nuclear movement, whereas nuclear envelope proteins are involved in movement through microtubule formation. Positioning of the microtubule-organizing center, which is proposed to be crucial for nuclear movement, is regulated by Nodal signaling and nuclear envelope proteins. The non-Smad JNK signaling pathway, which is downstream of Nodal signaling, regulates nuclear movement independently of the Smad pathway, and this nuclear movement is associated with Smad signal transduction toward the nucleus. Our study provides insight into the function of nuclear movement in Smad signaling toward the nucleus, and could be applied to the control of TGFß signaling.