How the Timing of Biological Processes Is Controlled and Modified at the Molecular and Cellular Level? 2.0

The correct timing of molecular and cellular events is critical for embryo development, cell/tissue homeostasis, and to functions in all organisms throughout their whole lives [...].

Immunomodulatory Effect of Infectious Disease of a Breastfed Child on the Cellular Composition of Breast Milk

Recent studies suggest that the content of immune components in milk is influenced by the mother's health and also by the infant she feeds. We aimed to evaluate the effect of a child's respiratory tract infection on the cellular composition of breast milk (neutrophils, monocytes, eosinophils, lymphocytes, and their subpopulations). Twenty-six breastfeeding mothers whose children were hospitalized for respiratory tract infections were enrolled in the study. The control group consisted of 23 mothers of healthy children. Regarding the children, baseline laboratory blood tests were performed, and nasal swabs were taken for the presence of RS virus. In the next step, milk samples were collected from the mothers to assess the cellular composition of the milk, including neutrophils, monocytes, eosinophils, lymphocytes, and their subpopulations. Significantly higher percentages of T lymphocytes (helper and cytotoxic lymphocytes) were observed in the milk of the studied mothers. There was a significantly higher percentage of milk lymphocytes in the group of affected children with confirmed RSV etiology than in children with excluded RSV etiology. A significant positive correlation was observed between the duration of infection and the percentage of milk NK cells and between milk CD19 lymphocytes and the child's serum leukocytosis. This study may provide evidence of a link between cells in breast milk and disease in the breastfed infant. The severity of the infection, its duration, and the etiological agent of the infection may affect the cellular composition of milk.

Coronavirus Disease Pathophysiology: Biomarkers, Potential New Remedies, Comorbidities, Long COVID-19, Post Pandemic Epidemiological Surveillance

The toughest challenge modern biomedical research ever faced was the rapid understanding of the SARS-CoV-2 physiopathology [...].

The Role of Vitamin D in COVID-19 and the Impact of Pandemic Restrictions on Vitamin D Blood Content

Vitamin D is a hormone regulating the immune system and playing a pivotal role in responses to microbial infections. It regulates inflammatory processes by influencing the transcription of immune-response genes in macrophages, T cells, and dendritic cells. The proven role of vitamin D in many infectious diseases of the respiratory tract indicated that vitamin D should also play a role in SARS-CoV-2 infection. Vitamin D inhibits cytokine storm by switching the pro-inflammatory Th1 and Th17 to the anti-inflammatory Th2 and Treg response. Vitamin D is therefore expected to play a role in preventing, relieving symptoms, or treating SARS-CoV-2 infection symptoms, including severe pneumonia. There are several possible mechanisms by which vitamin D may reduce the risk of COVID-19 infection, such as induction of the transcription of cathelicidin and defensin. Also a nongenomic antiviral action of vitamin D and lumisterol, the molecule closely related to vitamin D, was reported. Despite this enormous progress, currently, there is still insufficient scientific evidence to support the claim that vitamin D supplementation may help treat COVID-19 infection. The pandemic restrictions were also shown to impact vitamin D uptake by limiting exposure to sunlight.

Restless legs syndrome in Parkinson's disease: relationship with quality of life and medication

OBJECTIVES

We aimed to disclose the relationship between restless leg syndrome (RLS) and antiparkinsonian treatment, and its effect on quality of life (QoL) in patients with Parkinson's disease (PD).

BACKGROUND

Previous studies documented the prevalence of RLS among patients with PD to be higher than in the general population, but conclusions regarding the aetiology and impact were contradictory.

METHODS

We examined 101 patients with idiopathic PD. All participants completed the five-dimension/five-level-EuroQoL questionnaire (EQ-5D-5L) and the International Restless-Legs-syndrome-study-group rating Scale (IRLS).

RESULTS

The prevalence of RLS was 22.77 %. There were no statistically significant differences in levodopa or dopamine agonists (DA) doses between RLS-positive and negative participants. However, the use of levodopa as the last night-time medication was connected with a higher risk of RLS (OR=2.049, p=0.041). There was significantly lower prevalence of RLS in patients after surgical treatment for PD (p=0.024). Participants with RLS were at a greater risk for sleep disturbances (OR=3.866, p=0.023) and excessive daytime sleepiness (OR=7.202, p<0.001). Greater RLS symptoms were associated with worse QoL (higher IRLS score predicted higher EQ5D5L score, p=0.023).

CONCLUSION

RLS is prevalent among PD patients and night-time dopaminergic over-excitation with levodopa plays an important role in its pathogenesis. Since the symptoms of RLS are associated with decreased QoL, early accurate diagnosis and appropriate adjustment of dopaminergic therapy can lead to immediate relief from RLS symptoms and to QoL improvement (Tab. 4, Fig. 1, Ref. 34).

Reciprocal interactions between mesenchymal stem cells and macrophages

Mesenchymal stem cells (MSCs) are used as therapeutic agents for the treatment of a wide spectrum of diseases, as well as for the regeneration and healing of burns and wounds. MSCs have an immunomodulatory effect and influence the phenotype and functions of immune cells, including macrophages, which in turn prime and license the MSCs. We discuss the new findings on the feedback loop between MSCs and macrophages and its consequences on the outcome of MSC therapies.

P–275 Development of a prediction model using machine learning on small noncoding RNA biomarkers for non-invasive selection of high-quality embryos for the in vitro fertilization process

Study question

The aim of the study was to identify molecules in the embryo culture medium as important predictive biomarkers of high-quality embryos

Summary answer

The study identified 14 canonical iso-miRNA molecules that prognostically determine the quality of the embryo with a prediction accuracy with 95% sensitivity and 80% specificity.

What is known already

The quality of the embryo for the success of the IVF process is not specifically diagnosed, only morphological features (monitoring in the embryoscope) are considered. Embryo quality selection systems have likely reached their peak. The success rate of the IVF process is only 29%.; it is therefore necessary to look for other biomarkers. The oocyte itself can significantly predict the development of the early embryo,as it is a supplier of RNA and cellular mechanisms. However, collection follicular fluid is technically demanding. The probability of oocyte fertilization does not reach the required percentage therefore other embryological techniques multiply the economic costs.

Study design, size, duration

Women (n = 734) who visited the IVF centre were recruited for the study. Oocytes were collected from 54 of them and used for IVF. After 4/5-day embryo cultivation, the best quality embryo was selected and used for implantation into the uterus. The culture medium has been collected from 60 embryos during 3 years (2018–2020). Written informed consent was obtained from all patients. The study has been approved by the Ethical committee of the Košice governing region

Participants/materials, setting, methods

We used fresh/frozen culture media of embryos selected using an embryoscope. Further, information regarding the success of IVF, pregnancy and IVF failure was collected. Culture media libraries of noncoding small RNAs (miRNAs) were examined using massively parallel sequencing on the Illumina platform. Obtained data was processed with freely available bioinformatic tools and machine learning. For methods with different models, the number of predictive biomarkers and specific prognostic-predictive molecules were selected.

Main results and the role of chance

The main results of the study specifically identify ncRNA molecules that prognostically and predictively select a high-quality embryo suitable for IVF transmission from a low-quality embryo with 95% sensitivity and 80% specificity with an average accuracy of 85% in 4 different models. We also determined the minimum of 14 miRNA as prediction biomarkers. The developed model can predict embryo quality from the culture medium based on ncRNA results from sequence data and set the cut-off value for the expression and significance of individual miRNA molecules with respect to embryo quality. Furthermore, positive and negative correlations of miRNA molecules with different distributions in a high-quality embryo compared to a low-quality embryo were determined. The molecules identified in the embryo culture medium were organized according to their importance, resp. significance based on their significance coefficient. So far, there is no evidence of pending patents regarding the distribution of specific canonical miRNAs and iso-miRNA molecules analysed by massively parallel sequencing in terms of biological competence and embryo quality determination with multifactorial consideration of its variation. This is the first study focused on the success of the IVF process based on embryo quality prediction.

Limitations, reasons for caution

Exploratory data need to be validated in a larger scale study.

Wider implications of the findings: The given miRNA molecules and the software model can be used as a safe,non-invasive diagnostic test for the selection of a highly competent embryo. Canonical and iso-miRNA molecules from the study can be used in other forms of diagnostic assays, such as specific embryo selection probes and, plate hybridization assay.

Trial registration number

non clinical trials

The Assessment of the Usefulness of Selected Markers in the Diagnosis of Chronic Kidney Disease in Children

INTRODUCTION

The kidney deterioration, which starts in childhood often leads to end-stage renal failure in the future. Therefore, searching for an early, sensitive, and specific biomarkers became a paramount for chronic kidney disease diagnosis. The aim of this study was the assessment of markers: KIM-1, FGF-23, NAG, NGAL, and uromodulin for diagnosis of preclinical phase of the disease in children.

PATIENTS AND METHODS

59 children (15 boys, 44 girls from 6 months to 17 years old) with kidney disorders, which had clinical indications for renoscintigraphy, were included in the study. All patients were divided depending on the result of renoscintigraphy (renal scarring vs normal kidney picture) and depending on the level of estimated glomerular filtration rate (glomerular hyperfiltration vs normal filtration rate). The concentration of uromoduline, KIM-1, FGF-23, NAG, and NGAL in serum and of NGAL and uromoduline in urine were measured in all studied groups.

RESULTS

The children with glomerular hyperfiltration had a statistically significantly higher serum values of FGF-23 and NGAL than the children with normal filtration rate (P < .05). There were no statistically significant differences in serum concentrations of tested markers in children with renal scars in comparison to children with normal renal image. There was no statistically significant difference in the concentration of tested markers in urine.

CONCLUSIONS

The study confirmed the possible usefulness of FGF-23 and NGAL in detecting the preclinical-stage of renal disease associated with glomerular hyperfiltration in children. The study do not allow to indicate markers, which could be useful in the early diagnosis of kidney damage visible in the scintigraphic examination.

The Effect of Passive Exposure to Tobacco Smoke on the Immune Response in Children with Asthma

Introduction: There are a few publications about the impact of tobacco smoke on the children's immune system. Material and Methods: The study group consisted of 43 children with asthma. The control group consisted of 37 healthy children. The exposure to tobacco smoke was assessed by the presence of the cotinine in the urine (metabolit of nicotine). Results: The group of children with asthma exposed to tobacco smoke had significantly higher levels of the IL-1 and lower levels IL-4 than children not exposed to the passive smoking. The children from the control group exposed to tobacco smoke had a significantly higher concentration of IL-4 than unexposed children. In the whole analyzed population, there was a significant positive correlation between cotinine-IL1 and cotinine-CRP. Conclusion: In this study we found that the passive exposure to tobacco smoke has the immunomodulatory effects on the immune system.

Macrophages in diabetes mellitus (DM) and COVID-19: do they trigger DM?

Diabetes mellitus (DM) augments the risk of hospitalization and mortality resulting from viral, bacterial, or fungal pathogen infection. This has been also true for the past SARS and MERS, and current SARS-CoV-2 coronavirus epidemics. Clinical data indicate that SARS-CoV-2 infection triggers a severe course of COVID-19 more frequently in diabetic than non-diabetic patients. Here we overview the cellular and molecular mechanisms associated with this phenomenon. We focus on alterations in the immune cells, especially monocytes and macrophages, involved in innate immune response and inflammatory processes, which differ in type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM). We also describe the DM-related changes in the monocyte/macrophages functions, how they could lead to the severe outcome of SARS-CoV-2 infection, and importantly, if and how they could initiate DM in DM-susceptible patients.

Development of child immunity in the context of COVID-19 pandemic

Children, because of having an immature immune system, are usually more prone than the adults to the microbial infections and have more severe symptoms, which is especially true for the newborns, and very young children. However, the review of clinical data from the current COVID-19 pandemic indicates otherwise. We discuss here what are the main features and components of children's immune system, the role of maternal transmission of immunity, and what are the possible explanations for the seemingly lower infection rate and severity of COVI-19 in children.

Presynaptic GABAA Receptors Modulate Thalamocortical Inputs in Layer 4 of Rat V1

Fast inhibitory GABAergic transmission plays a fundamental role in neural circuits. Current theories of cortical function assume that fast GABAergic inhibition acts via GABAA receptors on postsynaptic neurons, while presynaptic effects of GABA depend on GABAB receptor activation. Manipulations of GABAA receptor activity in vivo produced different effects on cortical function, which were generally ascribed to the mode of action of a drug, more than its site of action. Here we show that in rodent primary visual cortex, α4-containing GABAA receptors can be located on subsets of glutamatergic and GABAergic presynaptic terminals and decrease synaptic transmission. Our data provide a novel mechanistic insight into the effects of changes in cortical inhibition; the ability to modulate inputs onto cortical circuits locally, via presynaptic regulation of release by GABAA receptors.

Prevalent placement error of deep brain stimulation electrode in movement disorders (technical considerations)

BACKGROUND

Deep brain stimulation is an effective and safe technique. Displacement of the electrode relative to the optimal stimulation site can lead to insufficient effect and sometimes to the need of operative electrode re-position.

OBJECTIVE

This study was aimed to analyse targeting accuracy of deep brain stimulation electrode implantation to subthalamic nucleus (STN) and globus pallidus internus (Gpi). It detected possible causes of inaccuracy and prevalent shift to certain direction.

METHODS

Targeting accuracy was analysed in 47 patients with Parkinson´s disease (PD) and 11 patients with dystonia with bilateral implantation of deep brain stimulation electrodes between years 2009 and 2016.

RESULTS

A shift of electrode to prevalent direction was observed on the left side to medial and posterior and on the right side to lateral direction. Greater shift was observed on the left side and in a higher angulation of trajectory laterally. Movement of the electrode, because of its traction in anchoring device, was identified as a possible factor for prevalent electrode shift. Calibration of stereotactic coordinates to correct prevalent shift was used.

CONCLUSION

Targeting inaccuracy is the result of accumulation of errors in individual steps of electrode implantation. Direction of the shift can be random or it can be toward a prevalent direction. A correction of prevalent error can prevent a suboptimal electrode placement (Tab. 3, Fig. 11, Ref. 29).

Graft-Infiltrating Macrophages Adopt an M2 Phenotype and Are Inhibited by Purinergic Receptor P2X7 Antagonist in Chronic Rejection

Macrophages exhibit diverse phenotypes and functions; they are also a major cell type infiltrating chronically rejected allografts. The exact phenotypes and roles of macrophages in chronic graft loss remain poorly defined. In the present study, we used a mouse heart transplant model to examine macrophages in chronic allograft rejection. We found that treatment of C57BL/6 mice with CTLA4 immunoglobulin fusion protein (CTLA4-Ig) prevented acute rejection of a Balb/c heart allograft but allowed chronic rejection to develop over time, characterized by prominent neointima formation in the graft. There was extensive macrophage infiltration in the chronically rejected allografts, and the graft-infiltrating macrophages expressed markers associated with M2 cells but not M1 cells. In an in vitro system in which macrophages were polarized into either M1 or M2 cells, we screened phenotypic differences between M1 and M2 cells and identified purinergic receptor P2X7 (P2x7r), an adenosine triphosphate (ATP)-gated ion channel protein that was preferentially expressed by M2 cells. We further showed that blocking the P2x7r using oxidized ATP (oATP) inhibited M2 induction in a dose-dependent fashion in vitro. Moreover, treatment of C57BL/6 recipients with the P2x7r antagonist oATP, in addition to CTLA4-Ig treatment, inhibited graft-infiltrating M2 cells, prevented transplant vasculopathy, and induced long-term heart allografts survival. These findings highlight the importance of the P2x7r-M2 axis in chronic rejection and establish P2x7r as a potential therapeutic target in suppression of chronic rejection.

Differential levels of stress proteins (HSPs) in male and female Daphnia magna in response to thermal stress: a consequence of sex-related behavioral differences?

In two independent experiments, we compared: (1) water depth selection (and accompanying temperature selection) by male and female Daphnia magna under different kinds of environmental stress, including the presence of filamentous cyanobacteria, the risk of predation from fish, and the presence of toxic compounds; and (2) sex-dependent production of heat shock proteins (HSP60, 70, and 90) in response to a sudden change in temperature. Male D. magna selected deep water strata, which offer a relatively stable environment, and thereby avoided the threat of predation and the presence of toxic compounds in surface waters. Correlated with this behavior, males reduce their molecular defenses against stress, such as the production of heat shock proteins (HSPs), and do not maintain the physiological machinery that triggers an increase in HSP levels in response to stress. In contrast, female D. magna actively select habitats that offer optimal conditions for growth and production of offspring. Consequently, females are exposed to variable environmental conditions that may be associated with increased stress. To permit survival in these different habitats, D. magna females require molecular mechanisms to protect their cells from rapid changes in stress levels. Thus, they maintain high constitutive levels of the heat shock proteins from HSP 60, 70, and 90 families, and they have the potential to further enhance the production of the majority of these proteins under stress conditions. The results of this study indicate that the separate habitats selected by male and female D. magna result in different patterns of HSP production, leading us to hypothesize that that male and female Daphnia magna adopt different strategies to maximize the fitness of the species.

Hermes is a localized factor regulating cleavage of vegetal blastomeres in Xenopus laevis

We have identified the RNA-binding protein Hermes in a screen for vegetally localized RNAs in Xenopus oocytes. The RNA localizes to the vegetal cortex through both the message transport organizer (METRO) and late pathways. Hermes mRNA and protein are both detected at the vegetal cortex of the oocyte; however, the protein is degraded within a several hour period during oocyte maturation. Injection of antisense morpholino oligonucleotides (HE-MO) against Hermes caused a precocious reduction in Hermes protein present during maturation and resulted in a phenotype characterized by cleavage defects in vegetal blastomeres. The phenotype can be partially rescued by injecting Hermes mRNA. These results demonstrate that the localized RNA-binding protein Hermes functions during oocyte maturation to regulate the cleavage of specific vegetally derived cell lineages. Hermes most likely performs its function by regulating the translation or processing of one or more target RNAs. This is an important mechanism by which the embryo can generate unique cell lineages. The regulation of region-specific cell division is a novel function for a localized mRNA.

RNA localization and its role in the spatially restricted protein synthesis

RNA localization is an evolutionarily conserved phenomenon that occurs in uni- and multi-cellular animal and plant species. Localized RNA plays a role in the establishment of cell polarity and/or the determination of cell fate. In recent years, it became evident that the major function of RNA localization is the creation of a high concentration of proteins in specific cellular compartments. The movement of RNA involves interactions between targeting signals within the RNA molecule, cytoskeleton, and molecular motors. Translocating RNA must be translationally silent, and on-site translation at the destination site requires a de-repression mechanism. This is probably achieved by sequestering RNA and the regulators of translation within the multiprotein RNP complexes that co-translocate all the components to the ultimate destination within the cell.

Accessory nuclei revisited: the translocation of snRNPs from the germinal vesicle to the periphery of the future embryo

Oocytes of certain insects contain peculiar organelles termed accessory nuclei (AN). These organelles originate by budding off from the envelope of the oocyte nucleus and contain 1-2 dense inclusions immersed in a translucent ground substance. We have demonstrated that in the wasp Vespula germanica each inclusion consists of two elements: a spherical body, and a hemispherical structure composed of numerous 20-30 nm particles. Immunoelectron microscopy and whole-mount in situ hybridization have shown that the inclusions contain AgNOR-staining proteins, p80-coilin, Sm proteins, and small nuclear RNAs (snRNAs). These results indicate that the inclusions and hemispherical structures are homologous to Cajal bodies and B-snurposomes of Xenopus germinal vesicles, respectively. During previtellogenesis, AN (together with their Cajal bodies) migrate to the cortical ooplasm of the oocyte where they reside at least until the onset of embryogenesis. We suggest that AN are vehicles for the transport and localization of snRNPs to the periphery of the oocyte, i.e., to the region where the blastoderm of the embryo develops and where there is a requirement for a high concentration of RNA-processing factors.

Chromatin elimination--an oddity or a common mechanism in differentiation and development?

Over many decades, a great number of exceptions from the rule of equal segregation of the chromosomes during cell division have been found in different animal species. The most diversified is the process of chromosome re-arrangement that takes place during the specification of soma versus germ-line cell fate in the embryos from the whole spectrum of animal phyla. In nematodes, copepodes, insects, hagfish, and marsupials, the chromatin/chromosome elimination is a common path of normal cell differentiation and development. This also raises the question of the mechanisms and factors that promote elimination in pre-somatic cell lines and/or inhibit the elimination in the prospective germ cells. We will discuss the possible role of the germ plasm in this process.

Balbiani bodies in cricket oocytes: development, ultrastructure, and presence of localized RNAs

Formation of two spherical Balbiani bodies along the long axis of previtellogenic oocytes in Acheta domesticus was demonstrated by differential interference microscopy. The structures form adjacent to and on opposite sides of the germinal vesicle, the anterior body first. Each migrates to the nearest pole of the elongating oocyte and retains its spherical structure until occluded from view by accumulating yolk. In situ hybridization, immunocytochemistry, and confocal immunofluorescent microscopy showed Balbiani body components to include y-tubulin, alpha-tubulin, EF1alpha, and several RNAs homologous to localized Xenopus RNAs implicated in embryonic axis formation or germ cell determination. The latter include Xcat2, Xwnt11, Xlsirt, and Xpat. Balbiani body ultrastructure includes a dense cloud of tubular mitochondria, rough ER, Golgi-like membrane aggregates, and microtubules. The results suggest that molecules and mechanisms specifying early determinative events for embryogenesis in vertebrates and insects are highly conserved and that Balbiani bodies may have a role in establishing developmental asymmetry in the cricket.

RNA localization and germ cell determination in Xenopus

In many organisms the proper development of the embryo depends on the asymmetrical distribution of maternal RNAs and proteins in the egg. Although the Xenopus oocyte is radially symmetrical it contains distinct populations of maternal RNAs that are localized either in the animal or vegetal pole. The process of localization of RNAs in Xenopus oocytes occurs during the long period of oocyte differentiation and growth that is accompanied by the elaboration of oocyte polarity. Some of the vegetally localized RNAs, such as Vg1, VegT, and Xwnt11, are involved in axial patterning and germ layer specification. Others, such as Xdazl and Xcat2, which are located in the germ plasm, are likely to play a role in the specification of germ cell fate. We will discuss the different aspects of RNA localization in Xenopus in the context of the differentiation of the germ cells and the development of the oocyte polarity.

Mitochondrial ribosomal RNA in the germinal granules in Xenopus embryos revisited

Germ cells of various animals contain a determinant that is called the germ plasm. In amphibians such as Xenopus laevis, the germ plasm is composed of mitochondria and electron dense germinal granules that are embedded in a fibrillar matrix. Previous reports indicated that one of the components of germinal granules was mitochondrial large and small ribosomal RNA (mtlrRNA and mtsrRNA). Utilizing a modified procedure for electron microscopy in situ hybridization, we investigated the distribution of these RNAs along with other components of the germ plasm in Xenopus laevis embryos. We found, that contrary to previous reports, the mtlrRNA and mtsrRNA were located in close vicinity to the germinal granules but were not major constituents of granules. The majority of the mtlrRNA and mtlsrRNAs was present inside the mitochondria and in the germ plasm matrix.

The vegetally localized mRNA fatvg is associated with the germ plasm in the early embryo and is later expressed in the fat body

Vegetally localized RNAs in Xenopus oocytes have been implicated in the establishment of the primary germ layers and the formation and development of the primordial germ cells. fatvg mRNA is localized through the late pathway to the vegetal cortex. Like Vg1 mRNA fatvg is distributed throughout the entire cortex; however, unlike Vg1 there is a small fraction of the fatvg mRNA that is associated with the mitochondrial cloud. In early cleavage stage embryos, fatvg mRNA is associated with the germ plasm located at the tips of the vegetal blastomeres of the embryo. While several localized RNAs that follow the Message Transport Organizer (METRO) pathway have been found in the germ plasm in embryos, fatvg is a late pathway RNA that is associated with the germ plasm. In tadpoles, fatvg mRNA shows a novel pattern of expression which is distinct from the germ cell lineage and is detected at the dorso-anterior margin of the endodermal mass along the midline in two clusters of cells. fatvg mRNA expression is also detected later in the developing fat bodies, the major adipose tissues of the frog.

The targeting of Xcat2 mRNA to the germinal granules depends on a cis-acting germinal granule localization element within the 3'UTR

The germ cell lineage is specified by the germ plasm, which in Xenopus laevis contains putative determinants called germinal granules. The pathway through which these structures form and how their components are assembled remain unclear. Using a combination of electron microscopy and in situ hybridization with the germinal granule-associated Xcat2 mRNA we demonstrated that the granules were derived from a branching network of granulofibrillar material within the mitochondrial cloud. Targeting of Xcat2 mRNA to the germinal granules depended on a 164-nt 3'UTR germinal granule localization element (GGLE; nt 631-795) that was distinct from the previously defined mitochondrial cloud localization element (MCLE; nt 403-630; Y. Zhou and M. L. King, 1996, Development 122, 2947-2953). This demonstrated that the Xcat 3'UTR contains a compound localization element consisting of a general element (MCLE) targeting the RNA to the mitochondrial cloud and a second element (GGLE) responsible for targeting to the germinal granules within the cloud. The GGLE when fused to Xlsirt RNA was sufficient to target this nongranule mitochondrial cloud-associated RNA to the germinal granules. This is the first example of a localization element involved in targeting an mRNA to a specific subcellular target such as the germinal granules and suggests that cis-acting elements on RNAs play an important role in the assembly of germinal granules and, therefore, the establishment of the germ cell lineage.

fatvg encodes a new localized RNA that uses a 25-nucleotide element (FVLE1) to localize to the vegetal cortex of Xenopus oocytes

Vegetally localized transcripts have been implicated in a number of important biological functions, including cell fate determination and embryonic patterning. We have isolated a cDNA, fatvg, which encodes a localized maternal transcript that exhibits a localization pattern reminiscent of Vg1 mRNA. fatvg is the homologue of a mammalian gene expressed in adipose tissues. The fatvg transcript, unlike Vg1 which localizes strictly through the Late pathway, also associates with the mitochondrial cloud that is characteristic of the METRO or Early pathway. This suggests that fatvg mRNA may utilize both the METRO and Late pathways to localize to the vegetal cortex during oogenesis. We have dissected the cis-acting localization elements of fatvg mRNA and compared these elements with Vg1 mRNA. Our results indicate that, like most localized RNAs, in a variety of systems, transcripts of fatvg contain localization elements in the 3′UTR. The 3′UTR of fatvg mRNA contains multiple elements that are able to function independently; however, it functions most efficiently when all of the elements are present. We have defined a short 25-nucleotide element that can direct vegetal localization as a single copy. This element differs in sequence from previously described Vg1 localization elements, suggesting that different localization elements are involved in the localization of RNAs through the Late pathway.

Extrachromosomal rDNA and polarity of pro-oocytes during ovary development in Creophilus maxillosus (Coleoptera, Staphylinidae)

In telotrophic ovary of Creophilus maxillosus, the differentiation of the oocyte and nurse cells takes place within the linear clusters of sister oogonial cells. The amplification of rDNA occurs in the nuclei of pro-oocytes which are the most posterior cells of the clusters. During the consecutive oogonial divisions extrachromosomal rDNA segregates preferentially to the pro-oocyte of the next generation. We analyzed the ultrastructure of pro-oocytes and pro-nurse cells in the early and late phase of rDNA amplification in pupal ovary of Creophilus maxillosus. We found that pro-oocytes of the same generation contain variable amounts of extrachromosomal rDNA and that the presence of extra DNA is not limited to the nuclei of pro-oocytes; extra DNA is also present in the nuclei of some pro-nurse cells. Pro-oocytes can experience partial loss of extrachromosomal DNA during early oogonial divisions which is caused by the imprecise segregation of this material to the posterior pole. We believe that this imperfect segregation is a source of extrachromosomal DNA present in the nuclei of pro-nurse cells. Ultrastructural analysis showed that multiple nucleoli do not disperse in oogonial mitoses but remain associated with extrachromosomal chromatin and segregate with it to the posterior pole of the pro-oocyte. We also analyzed the ultrastructure of the germ plasm--a cytoplasmic structure present at the posterior pole of pro-oocytes. We have found that this structure contains spectrin and at the ultrastructural level is strikingly similar to the spectrosome which is present in germline cells of Drosophila. We also found spectrin in the intercellular bridges which connect oogonial cells and are known to contain fusomes.

Joint action of two RNA degradation pathways controls the timing of maternal transcript elimination at the midblastula transition in Drosophila melanogaster

Maternally synthesized RNAs program early embryonic development in many animals. These RNAs are degraded rapidly by the midblastula transition (MBT), allowing genetic control of development to pass to zygotically synthesized transcripts. Here we show that in the early embryo of Drosophila melanogaster, there are two independent RNA degradation pathways, either of which is sufficient for transcript elimination. However, only the concerted action of both pathways leads to elimination of transcripts with the correct timing, at the MBT. The first pathway is maternally encoded, is targeted to specific classes of mRNAs through cis-acting elements in the 3'-untranslated region and is conserved in Xenopus laevis. The second pathway is activated 2 h after fertilization and functions together with the maternal pathway to ensure that transcripts are degraded by the MBT.

Contribution of METRO pathway localized molecules to the organization of the germ cell lineage

To elucidate the potential role of localized components in the specification of the germ cell lineage we analyzed the composition of the germ plasm in Xenopus laevis oocytes and early embryos with respect to the vegetally-localized RNAs. We focused on Xlsirts, Xcat2, and Xwnt11 transcripts that are localized to the vegetal cortex through a region of the mitochondrial cloud called the messenger transport organizer (METRO) that also contains the nuage or germ plasm. At the ultrastructural level Xcat2 mRNA was detected on germinal granules while Xlsirts and Xwnt11 were associated with a fibrillar network of the germ plasm in stage-1 and stage-4 oocytes. In embryos, we found that all three RNAs remained associated with the germ plasm. Vg1 mRNA, a transcript localized through the late pathway, was excluded from the germ plasm in oocytes and embryos. Addtionally, we detected the protein spectrin within 16 cell nests of germ cells, in a structure reminiscent of the Drosophila spectrosome. Spectrin was detected in the mitochondrial cloud and was found in the germ plasm during embryogenesis. These data indicate that the various RNAs found within METRO and the protein spectrin are integral components of the Xenopus germ plasm with the RNAs being associated with different subcellular structures. They also suggest that the pathway through which RNAs are localized during oogenesis may be an important factor in biasing their distribution into specific cell lineages. The presence of Xwnt11 in the germ cell lineage suggests that a wnt-directed signaling pathway may be involved in germ cell specification. differentiation or migration.

Apparent continuity between the messenger transport organizer and late RNA localization pathways during oogenesis in Xenopus

The localization of RNAs at the vegetal cortex in Xenopus oocytes is a complex process, involving at least two different pathways. The early, or messenger transport organizer (METRO), pathway, localizes RNAs such as Xlsirts, Xcat2 and Xwnt11 during stages 1 and 2 of oogenesis, while the late pathway localizes RNAs such as Vg1 during stages 2-4. We demonstrate that the onset of Vg1 localization is characterized by its microtubule-independent binding to a subdomain of the endoplasmic reticulum (ER). The formation of this unique ER structure is intimately associated with the movement of the mitochondrial cloud toward the vegetal cortex. In addition, we demonstrate that the mitochondrial cloud contains a gamma-tubulin-positive structure that may function as a microtubule organizing center for establishing microtubule tracks for Vg1 localization. These data, support, although they do not prove, a model in which the development of the late pathway machinery relies upon the prior functioning of the early pathway.

Elaboration of the messenger transport organizer pathway for localization of RNA to the vegetal cortex of Xenopus oocytes

Previous studies demonstrated that there were two pathways, the messenger transport organizer (METRO) or early and the Vg1 or late, which function during stages 1 to 3 of oogenesis for the localization of RNAs at the vegetal cortex of Xenopus oocytes. In the present study we analyzed the properties of the METRO pathway, which localizes Xlsirt, Xcat2, and Xwnt11 RNAs to a specific region of the vegetal cortex during stage 1 of oogenesis. A combination of methodologies involving both fixed material and living oocytes was used to analyze RNA localization. We show that in early diplotene pre-stage 1 oocytes (25-50 microm in diameter) both endogenous and injected exogenous METRO RNAs translocated to multiple mitochondrial aggregates (pre-mitochondrial clouds) that surround the germinal vesicle (GV). However, by early stage 1 (diplotene oocytes, 50-200 microm), all three of the RNAs discriminated between the different clouds and translocated exclusively within the METRO of a single mitochondrial cloud. Therefore, in stage 1 diplotene oocytes there is a unique mechanism causing a change in the intrinsic property of the mitochondrial clouds which designates one of them as the RNA transport vehicle. During translocation through the cytoplasm Xlsirt and Xcat2 RNAs were detected associated with cytoplasmic particles of different morphologies. Additionally, we also found that the translocation of RNAs through the early or METRO pathway, unlike that of the late pathway, occurred in the absence of intact microtubule and actin microfilament cytoskeletal elements. This supports a cytoskeletal-independent model for localization of RNAs through the METRO pathway.

Membrane-bound or soluble truncated RT1.Aa rat class I major histocompatibility antigens induce specific alloimmunity

Transfectants that express membrane-bound (MB) or secrete soluble truncated (TR) rat class I RT1.Aa major histocompatibility (MHC) antigens induce alloimmunity in vivo. The MB-RT1.Aa was produced by transfecting the full-length RT1.Aa cDNA, including the alpha 1, alpha 2, and alpha 3, transmembrane and intracellular domains. The TR-RT1.Aa cDNA insert included only the extracellular alpha 1, alpha 2, and alpha 3 domains; a stop codon was placed in front of the transmembrane domain. Following full-length sequencing, MB-RT1.Aa and TR-RT1.Aa cDNAs were translated in vitro into glycosylated MB-RT1.Aa (45 kDa) and TR-RT1.Aa (36 kDa) proteins, respectively. Each cDNA construct was individually subcloned into the pSG5 vector before transfection into Buffalo (BUF; RT1b) hepatoma cells. FACscan analysis with anti-RT1.Aa-specific R2/15S monoclonal antibody (MAb) confirmed surface expression of RT1.Aa molecules on the MB-RT1.Aa, but not on the TR-RT1.Aa, transfectants. In contrast, enzyme-linked immunoadsorbent assays documented the presence of soluble RT1.Aa molecules in supernates from cells transfected with the TR-RT1.Aa, but not from cells transfected with the MB-RT1.Aa, cDNA. Subcutaneous injection of MB-RT1.Aa or TR-RT1.Aa transfectants to BUF or Wistar Furth (WF; RT1u) rats induced accelerated rejection of ACI (RT1a) but not third-party Brown Norway (RT1n) heart allografts. Furthermore, supernates of TR-RT1.Aa, but not of MB-RT1.Aa, transfectants immunized WF hosts toward ACI hearts. Thus, both intact MB-RT1.Aa and soluble TR-RT1.Aa class I alloantigens induce potent sensitization against alloantigens.

Id gene activity during Xenopus embryogenesis

The activity of bHLH transcription factors that are involved in cell determination and differentiation is inhibited by Ids, HLH proteins lacking the basic amino acid sequence element. In order to determine the role of Id during development, we have isolated and characterized the Id genes expressed in Xenopus embryos. Three cDNAs were characterized: XIdIa and XIdIb, which are transcribed from one gene but differentially spliced in the 3' untranslated part, and XIdII which is transcribed from a second copy of the gene. One of the two forms of the differentially spliced mRNAs exhibits, 30 nucleotides upstream from the AATAAA site, a sequence box homologous to the cytoplasmic polyadenylation element (CPE) which is present also in Id2 and Id3 mRNAs from higher vertebrates. This raises the question of whether this CPE-like element may link Id mRNA polyadenylation and translation to the cell cycle metabolism. The Xenopus Id gene is transcribed at low level in oocytes and at high level in embryos, after midblastula transition, in a large number of tissues, including the notochord, neural tube, eye, ear, neural crest cells, presomitic mesoderm, myotomes, tailbud and dorsal fin. In myotomes, expression is high in the areas of proliferating myoblasts and decreases as terminal differentiation proceeds, consistent with a function in cell determination and differentiation and possibly also in cell cycle regulation.

Two distinct pathways for the localization of RNAs at the vegetal cortex in Xenopus oocytes

We found that there are two major pathways by which RNAs are localized at the vegetal cortex during oogenesis of Xenopus laevis. One of these, through which Xlsirts, Xcat2 and Xwnt11 are localized, involves transport during stages 1 and 2 of oogenesis via a region of the mitochondrial cloud that we call the message transport organizer or METRO. This pathway involved three steps, transport of RNA from the GV to the mitochondrial cloud, sorting of the RNAs to specific regions of the METRO, and translocation to and anchoring at the vegetal cortex. These three RNAs exhibit a distinct pattern of spatial localization within the METRO when they approach the vegetal cortex. The other pathway is used by Vg1. We detected Vg1 throughout the oocyte cytoplasm during stages 1 and 2. During stage 3 it was translocated to the vegetal cortex and associated with the cortex overlapping the region at which the Xlsirt, Xcat2, and Xwnt11 RNAs are anchored. Our results also showed that anchoring of these RNAs was dependent in part on actin microfilaments, but was independent of microtubules. These results demonstrate a novel mechanism of translocation and RNA sorting used by RNAs several of which may be involved in the establishment of the embryonic body axis.

Delocalization of Vg1 mRNA from the vegetal cortex in Xenopus oocytes after destruction of Xlsirt RNA

The Xlsirts are a family of transcribed repeat sequence genes that do not code for protein. Xlsirt RNAs become localized to the vegetal cortex of Xenopus oocytes early in oogenesis, before the localization of the messenger RNA Vg1, which encodes a transforming growth factor-beta-like molecule involved in mesoderm formation, and coincident with the localization of Xcat2 transcripts, which encode a nanos-like molecule. Destruction of the localized Xlsirts by injection of antisense oligodeoxynucleotides into stage 4 oocytes resulted in the release of Vg1 transcripts but not Xcat2 transcripts from the vegetal cortex. Xlsirt RNAs, which may be a structural component of the vegetal cortex, are a crucial part of a genetic pathway necessary for the proper localization of Vg1 that leads to subsequent normal pattern formation.

The association of Xenopus nuclear factor 7 with subcellular structures is dependent upon phosphorylation and specific domains

The function of proteins is often regulated by their association with specific subcellular structures. Xenopus nuclear factor 7 (xnf7) is a putative transcription factor that is selectively retained in the cytoplasm from fertilization through the mid blastula transition (MBT). Cytoplasmic retention is dependent upon the presence of a 22-amino-acid cytoplasmic retention domain and the phosphorylation of two sites (site 1 and site 2) within the protein. We show that the N-terminal acidic domain of xnf7 transactivated a reporter gene in transfected cells, supporting its function as a transcription factor. During mitosis xnf7 was associated with the mitotic spindle and chromosomes, while during the short embryonic interphase it was associated with structures at the poles which were most likely centrosomes. The association with these structures was dependent upon the presence of protein domains and the phosphorylation of a specific phosphorylation site (site 2). In addition, we determined that association with the spindle or centrosomes was not necessary for cytoplasmic retention prior to the MBT. We suggest that the association of xnf7 with these structures is due to its interaction with other proteins that are colocalized.

Cytoplasmic retention of Xenopus nuclear factor 7 before the mid blastula transition uses a unique anchoring mechanism involving a retention domain and several phosphorylation sites

Xenopus nuclear factor 7 (xnf7) is a maternally expressed protein that belongs to the B-box zinc finger gene family consisting of transcription factors, protooncogenes, and ribonucleoproteins. Its function is regulated by retention in the cytoplasm from oocyte maturation until the mid blastula transition (MBT) when it reenters the nucleus. We defined a 22-amino acid cytoplasmic retention domain (CRD) in xnf7 that functioned cooperatively with two phosphorylation sites within the xnf7 molecule to retain the protein in the cytoplasm until the MBT. Deletion of this region or mutations in the phosphorylation sites resulted in the early entry of xnf7 into the nucleus. A mutation changing one of the phosphorylation sites to a glutamic acid resulted in the prolonged retention of the xnf7 protein in the cytoplasm until stages 9-10, well past the MBT. Additionally, a mutant form of xnf7 possessing a second nuclear localization signal at the COOH terminus was retained in the cytoplasm. This suggests that retention of xnf7 was not due to the masking of its NLS as is the case with NFkB and dorsal but was due to a novel anchoring mechanism in which the CRD interacts with an anchor protein. The CRD sequence is also found in another B-box zinc finger protein that is also retained in the cytoplasm until the MBT in the newt. Therefore, we believe that this may be an important mechanism whereby the function of a number of nuclear proteins is regulated during development.

Translocation of repetitive RNA sequences with the germ plasm in Xenopus oocytes

Xlsirts are a family of interspersed repeat RNAs from Xenopus laevis that contain from 3 to 13 repeat units (each 79 to 81 nucleotides long) flanked by unique sequences. They are homologous to the mammalian Xist gene that is involved in X chromosome inactivation. Xlsirt RNA appears first in the mitochondrial cloud (Balbiani body) in stage 2 oocytes and is then translocated as island-like structures to the vegetal cortex at early stage 3 coincident with the localization of the germ plasm. Exogenous Xlsirt RNA injected into oocytes translocates to the location of the endogenous RNA at that particular stage. The Xlsirt RNA repeat sequences are required for translocation and can cause the translocation of heterologous unique RNAs to the vegetal cortex.

Two upstream cysteines and the CAAX motif but not the polybasic domain are required for membrane association of Xlcaax in Xenopus oocytes

We have analyzed the role of several protein motifs in controlling the membrane association of the xlcaax-1 protein in Xenopus oocytes. Xlcaax-1 is a maternally expressed protein that during development is associated with the basal lateral membrane of polarized epithelial cells. It is enriched in the tubule cells of the adult kidney and several other organs that are involved in osmoregulation. Xlcaax-1 has a C-terminal CAAX sequence (CVVM) identical to that of N-ras, followed by two cysteines that are potential palmitoylation sites and a polybasic domain. Mutants were constructed that either deleted specific domains or changed specific amino acids of the consensus sequences in or near the CAAX motif. Synthetic mRNAs were injected into Xenopus oocytes and their protein products analyzed for their ability to associate with the oocyte plasma membrane. A mutation changing cysteine-588 of the CAAX box to serine or the inhibition of prenylation by lovastatin eliminated the membrane association of the protein. Mutation of either of the upstream cysteines (either 585 or 587) also inhibited the association of xlcaax-1 with the membrane. Unlike Ras, however, deletion of the polybasic domain had no effect on membrane binding. In addition, we show that xlcaax-1 binds ATP but not GTP.

The cloning and characterization of a localized maternal transcript in Xenopus laevis whose zygotic counterpart is detected in the CNS

We have cloned a cDNA (xlan4) from a Xenopus laevis oocyte cDNA library whose cognate mRNA is localized in the animal pole region of full grown oocytes. The cDNA can be translated in vitro to produce a predicted size protein of 35 kDa and, is also expressed in E. coli as a fusion protein. The conceptual protein encoded by the xlan4 cDNA is 17.5% proline rich and possesses several PEST sequences found in proteins with short half-lives. The xlan4 mRNA is 2.6 kb and during early development its titer decreases until the neurula stage after which it begins to reaccumulate. Northern blots on dissected embryos and in situ hybridization revealed that the zygotic expression is limited to the dorsal axial structures consisting primarily of the CNS. UV irradiation of the vegetal pole region immediately following fertilization that produces ventralized embryos results in a loss of zygotic xlan4 expression. In the adult, xlan4 mRNA is limited primarily to the brain. The presence of this mRNA in animal pole region which contributes to the future neural cell lineages suggests that this gene product may function either in the specification of neural cell types or in a neural specific function.