Human Prenatal Development Research Articles

Ganglioside SSEA-4 in Ewing sarcoma marks a tumor cell population with aggressive features and is a potential cell-surface immune target

Carbohydrate markers of immature cells during prenatal human development can be aberrantly expressed in cancers and deserve evaluation as immune targets. A candidate target in Ewing sarcoma is the globo-series ganglioside stage-specific embryonic antigen-4 (SSEA-4). We detected SSEA-4 expression on the cell surface of all of 14 EwS cell lines and in 21 of 31 (68%) primary EwS tumor biopsies. Among paired subpopulations of tumor cells with low versus high SSEA-4 expression, SSEA-4high expression was significantly and consistently associated with functional characteristics of tumor aggressiveness, including higher cell proliferation, colony formation, chemoresistance and propensity to migrate. SSEA-4low versus SSEA-4high expression was not related to expression levels of the EWSR1-FLI1 fusion transcript or markers of epithelial/mesenchymal plasticity. SSEA-4low cells selected from bulk populations regained higher SSEA-4 expression in vitro and during in vivo tumor growth in a murine xenograft model. T cells engineered to express SSEA-4-specific chimeric antigen receptors (CARs) specifically interacted with SSEA-4 positive EwS cells and exerted effective antigen-specific tumor cell lysis in vitro. In conclusion, with its stable expression and functional significance in EwS, SSEA-4 is an attractive therapeutic immune target in this cancer that deserves further evaluation for clinical translation.

O13 Benchmarking a human pluripotent stem cell-derived hair-bearing skin organoid model to prenatal skin

Abstract Introduction and aims Molecular regulation of mammalian skin development has been largely derived from murine studies. The lack of human studies stems primarily from the difficulties in prenatal human skin access. There is an important need to study human prenatal skin owing to the notable differences between human and mouse skin and the paucity of mechanistic understanding of congenital skin disorders. Methods We assembled the first comprehensive multiomic reference atlas of prenatal human skin (21 samples from 7 to 16 postconception weeks), combining single-cell (235 201 cells) and spatial transcriptomic data. We followed 84 skin organoids (SkOs) using single-cell analysis over a 5-month culture period and characterized the spatial organization of the skin in mature SkOs. Prenatal skin, SkO and any relevant pre-existing single-cell RNA-Seq datasets were integrated into the analysis. Cell–cell interactions and cell-lineage determination were explored using CellPhoneDB and trajectory inferences. We evaluated the differentiation trajectory alignment between prenatal skin and SkO using the Genes2Genes analysis. Results Our findings reveal predicted factors regulating the epithelial–mesenchymal crosstalk during human hair follicle formation; progressive expression of scar-promoting genes in later gestation, potentially contributing to scarless healing properties of human prenatal skin observed during the early stages of gestation and expression of genes causing genetic skin disorders in the same cell types in prenatal human skin and SkO. We also found that SkOs morphologically recapitulate human skin development from early (periderm formation and shedding) to late (cornification and hair follicle formation) stages. We also demonstrated that SkO and prenatal skin mesenchyme differentiation into hair follicle dermal condensate and dermal papilla is highly conserved at the cellular and molecular level. Conclusions SkOs faithfully recapitulate human prenatal skin development and are a valuable model for mechanistic studies on skin development including hair follicle biology and congenital skin disorders.

CRANIOMETRICAL CHARACTERISTICS OF THE HUMAN FETAL SKULL

The purpose of the study – to ascertain the regularities of the age-related dynamics ofmorphometric changes of the skull in the fetal period of human ontogenesis.Material and methods. 59 specimens and 12 computed tomography (CT) scans of theskulls of human fetuses aged from 4 to 10 months of intrauterine development (IUD)were studied. A complex of morphological research methods was applied, which includedanthropometry, morphometry, three- dimensional reconstruction and statistical analysis.The results. It has been established that the longitudinal and transverse dimensions, thecircumference of the cerebral part of the skull grow almost uniformly before birth, but bythe 5th month of the IUD, a more accelerated growth is observed, due to which the scatterdiagram has the appearance of a logarithmic dependence. A somewhat uneven growth ofthese morphometric indicators is also observed in the age-related changes in the width andupper height of the face. The growth of the facial angle during the fetal period was revealed,which can be explained by the development of the mandible («pushing» it forward). At the same time, the basilar angle slightly decreases during the fetal period of development,which can be explained by the increase in the brain volume. The basilar angle increaseswith the age of the fetus, but somewhat unevenly in leptins, i. e., until the beginning of the6th month, it almost does not change, during the 6th-7th months it increases intensively,and then slows down again until the end of the fetal period of IUD. In euryons, there isa uniform growth of the basilar angle throughout the fruiting period of development, andmore intensively than in the average morphotype – mesens. Analysis of the correlation offetal age, cranial index, and basilar angle size showed even more significant anatomicalvariability. Thus, if in dolicho- and mesomorphs the basilar angle grows almost uniformlyduring the fetal period, then in brachymorphs it first intensively decreases until the 6thmonth of development, and then begins to grow until the newborn period. It should be notedthat a similar feature is observed in the dynamics of age-related changes in the facial angle,in addition to slowing down its growth from the 8th month in dolichomorphs.Conclusions. 1. Regression analysis of the correlation of age, morphotype indicators, andbasilar and facial angles made it possible to establish patterns of individual morphometricvariability of the skull in the dynamics of the fetal period of prenatal human development,as well as to identify critical periods of morphogenesis of the brain and facial parts ofthe skull, which are 6-7 months in leptins, the 6th month – for brachymorphs and the 8thmonth – for dolichomorphs. 2. The size of the basilar angle of the skull is an importantdiagnostic and prognostic indicator in combination with indices that characterize themorphotype of the individual, for monitoring the normal development of the skull andbrain of the fetus.

Sex-Differential Gene Expression in Developing Human Cortex and Its Intersection With Autism Risk Pathways

BackgroundSex-differential biology may contribute to the consistently male-biased prevalence of autism spectrum disorder (ASD). Gene expression differences between males and females in the brain can indicate possible molecular and cellular mechanisms involved, although transcriptomic sex differences during human prenatal cortical development have been incompletely characterized, primarily due to small sample sizes. MethodsWe performed a meta-analysis of sex-differential expression and co-expression network analysis in 2 independent bulk RNA sequencing datasets generated from cortex of 273 prenatal donors without known neuropsychiatric disorders. To assess the intersection between neurotypical sex differences and neuropsychiatric disorder biology, we tested for enrichment of ASD–associated risk genes and expression changes, neuropsychiatric disorder risk genes, and cell type markers within identified sex-differentially expressed genes (sex-DEGs) and sex-differential co-expression modules. ResultsWe identified 101 significant sex-DEGs, including Y-chromosome genes, genes impacted by X-chromosome inactivation, and autosomal genes. Known ASD risk genes, implicated by either common or rare variants, did not preferentially overlap with sex-DEGs. We identified 1 male-specific co-expression module enriched for immune signaling that is unique to 1 input dataset. ConclusionsSex-differential gene expression is limited in prenatal human cortex tissue, although meta-analysis of large datasets allows for the identification of sex-DEGs, including autosomal genes that encode proteins involved in neural development. Lack of sex-DEG overlap with ASD risk genes in the prenatal cortex suggests that sex-differential modulation of ASD symptoms may occur in other brain regions, at other developmental stages, or in specific cell types, or may involve mechanisms that act downstream from mutation-carrying genes.

Neuroimmune mechanisms in autism etiology - untangling a complex problem using human cellular models.

Autism spectrum disorder (ASD) affects 1 in 36 people and is more often diagnosed in males than in females. Core features of ASD are impaired social interactions, repetitive behaviors and deficits in verbal communication. ASD is a highly heterogeneous and heritable disorder, yet its underlying genetic causes account only for up to 80% of the cases. Hence, a subset of ASD cases could be influenced by environmental risk factors. Maternal immune activation (MIA) is a response to inflammation during pregnancy, which can lead to increased inflammatory signals to the fetus. Inflammatory signals can cross the placenta and blood brain barriers affecting fetal brain development. Epidemiological and animal studies suggest that MIA could contribute to ASD etiology. However, human mechanistic studies have been hindered by a lack of experimental systems that could replicate the impact of MIA during fetal development. Therefore, mechanisms altered by inflammation during human pre-natal brain development, and that could underlie ASD pathogenesis have been largely understudied. The advent of human cellular models with induced pluripotent stem cell (iPSC) and organoid technology is closing this gap in knowledge by providing both access to molecular manipulations and culturing capability of tissue that would be otherwise inaccessible. We present an overview of multiple levels of evidence from clinical, epidemiological, and cellular studies that provide a potential link between higher ASD risk and inflammation. More importantly, we discuss how stem cell-derived models may constitute an ideal experimental system to mechanistically interrogate the effect of inflammation during the early stages of brain development.

Формирование транзиторных зон в дорсомедиальной и дорсолатеральной неокортикальных областях в раннем развитии человека

Introduction. Transient zones form during prenatal corticogenesis and disappear and are replaced by mature white and gray matter in postnatal ontogenesis. The growth trajectories of transient zones have not been completely characterized, and quantitative data describing these processes are still scarce. We aimed to describe the hemispheric wall stratification during 3–4 months of intrauterine development and clarify timing of major transient zone formation in dorsolateral and dorsomedial neocortical areas.Materials and methods. We examined 12 autopsy brain samples of human fetuses at postcoital weeks 8–15. Nissl, Mallory trichrome, and haematoxylin and eosin histological preparations were analyzed. Then we performed morphometric and statistical analyses.Results. Consecutive formation and growth of transient zones in hemispheric walls occur during early prenatal development at postcoital weeks 8–15. Nissl, Mallory trichrome, and haematoxylin and eosin histological preparations were analyzed. In the dorsomedial hemispheric wall, the development of transient zones is delayed compared to that in the dorsolateral one.Conclusion.The formation of transient zones in dorsomedial and dorsolateral hemispheric walls is characterized by regional heterochrony, which could account for neocortical area differentiation and needs further research. Keywords: transient zones, neocortex, neurogenesis, corticogenesis, human prenatal development

Nested Selves: Self-Organization and Shared Markov Blankets in Prenatal Development in Humans.

The immune system is a central component of organismic function in humans. This paper addresses self-organization of biological systems in relation to-and nested within-other biological systems in pregnancy. Pregnancy constitutes a fundamental state for human embodiment and a key step in the evolution and conservation of our species. While not all humans can be pregnant, our initial state of emerging and growing within another person's body is universal. Hence, the pregnant state does not concern some individuals but all individuals. Indeed, the hierarchical relationship in pregnancy reflects an even earlier autopoietic process in the embryo by which the number of individuals in a single blastoderm is dynamically determined by cell- interactions. The relationship and the interactions between the two self-organizing systems during pregnancy may play a pivotal role in understanding the nature of biological self-organization per se in humans. Specifically, we consider the role of the immune system in biological self-organization in addition to neural/brain systems that furnish us with a sense of self. We examine the complex case of pregnancy, whereby two immune systems need to negotiate the exchange of resources and information in order to maintain viable self-regulation of nested systems. We conclude with a proposal for the mechanisms-that scaffold the complex relationship between two self-organising systems in pregnancy-through the lens of the Active Inference, with a focus on shared Markov blankets.

Species-specific FMRP regulation of RACK1 is critical for prenatal cortical development

Fragile X messenger ribonucleoprotein 1 protein (FMRP) deficiency leads to fragile X syndrome (FXS), an autism spectrum disorder. The role of FMRP in prenatal human brain development remains unclear. Here, we show that FMRP is important for human and macaque prenatal brain development. Both FMRP-deficient neurons in human fetal cortical slices and FXS patient stem cell-derived neurons exhibit mitochondrial dysfunctions and hyperexcitability. Using multiomics analyses, we have identified both FMRP-bound mRNAs and FMRP-interacting proteins in human neurons and unveiled a previously unknown role of FMRP in regulating essential genes during human prenatal development. We demonstrate that FMRP interaction with CNOT1 maintains the levels of receptor for activated C kinase 1 (RACK1), a species-specific FMRP target. Genetic reduction of RACK1 leads to both mitochondrial dysfunctions and hyperexcitability, resembling FXS neurons. Finally, enhancing mitochondrial functions rescues deficits of FMRP-deficient cortical neurons during prenatal development, demonstrating targeting mitochondrial dysfunction as a potential treatment.

Expression of the schizophrenia associated gene FEZ1 in the early developing fetal human forebrain.

The protein fasciculation and elongation zeta-1 (FEZ1) is involved in axon outgrowth but potentially interacts with various proteins with roles ranging from intracellular transport to transcription regulation. Gene association and other studies have identified FEZ1 as being directly, or indirectly, implicated in schizophrenia susceptibility. To explore potential roles in normal early human forebrain neurodevelopment, we mapped FEZ1 expression by region and cell type. All tissues were provided with maternal consent and ethical approval by the Human Developmental Biology Resource. RNAseq data were obtained from previously published sources. Thin paraffin sections from 8 to 21 post-conceptional weeks (PCW) samples were used for RNAScope in situ hybridization and immunohistochemistry against FEZ1 mRNA and protein, and other marker proteins. Tissue RNAseq revealed that FEZ1 is highly expressed in the human cerebral cortex between 7.5-17 PCW and single cell RNAseq at 17-18 PCW confirmed its expression in all neuroectoderm derived cells. The highest levels were found in more mature glutamatergic neurons, the lowest in GABAergic neurons and dividing progenitors. In the thalamus, single cell RNAseq similarly confirmed expression in multiple cell types. In cerebral cortex sections at 8-10 PCW, strong expression of mRNA and protein appeared confined to post-mitotic neurons, with low expression seen in progenitor zones. Protein expression was observed in some axon tracts by 16-19 PCW. However, in sub-cortical regions, FEZ1 was highly expressed in progenitor zones at early developmental stages, showing lower expression in post-mitotic cells. FEZ1 has different expression patterns and potentially diverse functions in discrete forebrain regions during prenatal human development.

PECULIARITIES OF DEVELOPMENT OF THE HUMAN FACIAL REGION OF SKULL

PECULIARITIES OF DEVELOPMENT OF THE HUMAN FACIAL REGION OF SKULL

Neuromorphological Atlas of Human Prenatal Brain Development: White Paper.

Recent morphological data on human brain development are quite fragmentary. However, they are highly requested for a number of medical practices, educational programs, and fundamental research in the fields of embryology, cytology and histology, neurology, physiology, path anatomy, neonatology, and others. This paper provides the initial information on the new online Human Prenatal Brain Development Atlas (HBDA). The Atlas will start with forebrain annotated hemisphere maps, based on human fetal brain serial sections at the different stages of prenatal ontogenesis. Spatiotemporal changes in the regional-specific immunophenotype profiles will also be demonstrated on virtual serial sections. The HBDA can serve as a reference database for the neurological research, which provides opportunity to compare the data obtained by noninvasive techniques, such as neurosonography, X-ray computed tomography and magnetic resonance imaging, functional magnetic resonance imaging, 3D high-resolution phase-contrast computed tomography visualization techniques, as well as spatial transcriptomics data. It could also become a database for the qualitative and quantitative analysis of individual variability in the human brain. Systemized data on the mechanisms and pathways of prenatal human glio- and neurogenesis could also contribute to the search for new therapy methods for a large spectrum of neurological pathologies, including neurodegenerative and cancer diseases. The preliminary data are now accessible on the special HBDA website.

Abstract 4068: Ganglioside SSEA4 in Ewing sarcoma: A marker of tumor cells with highly aggressive features and a potential immune target

Abstract Cancers can aberrantly express carbohydrate antigens restricted to immature cells during prenatal human development, and these may be exploited for selective immune targeting. We studied expression and functional associations of the globo-series ganglioside stage-specific embryonic antigen 4 (SSEA4), a cell surface marker of human embryonic stem cells, in Ewing sarcoma (EwS). Flow cytometry revealed SSEA4 expression on the cell surface of each of 13 EwS cell lines, with moderate to high expression densities in 6 of 13 (46%) cell lines. Of 31 primary EwS tumor biopsies, 21 (68%) were SSEA4 positive by immunofluorescence staining. No associations of SSEA4 positivity with molecular or clinical disease parameters were found. Comparisons of paired tumor cell subpopulations with high and low/negative SSEA4 expression selected by cell sorting from 8 EwS cell lines revealed increased cell proliferation and colony formation of SSEA4high tumor cells, along with higher doxocrubicin chemoresistance and a higher propensity to migrate in transwell assays. SSEA4 negative cells selected from bulk populations of EwS cells regained SSEA4 expression during continued in vitro culture as well as after in vivo xenografting into immunodeficient mice. SSEA4high expression in EwS cells was not dependent on expression levels of the EWSR1-FLI1 fusion transcript or its direct targets, nor associated with markers of epithelial/mesenchymal plasticity. To retarget human T cells to SSEA4, we generated a second-generation, 41BBζ CAR using the antigen-binding domains of a murine anti-SSEA4 monoclonal antibody. SSEA4-specific CAR T cells specifically interacted with SSEA4 positive EwS cells in a strictly antigen-dependent manner, resulting in effective tumor cell lysis in vitro. We conclude that targeting of SSEA4 with CAR T cells or alternative immune therapeutics could be an attractive strategy to eliminate tumor cell subsets with high propensity to drive disease progression in EwS and therefore deserves further evaluation towards clinical translation. Citation Format: Silke Jamitzky, Bianca Altvater, Carolin Krekeler, Laura Hoen, Caroline Brandes, Lisa Richter, Julia Ebbinghaus, Laurin Ochs, Nicole Farwick, Katja Urban, Dennis Görlich, Ian Johnston, Rita Pfeifer, Claudia Rossig, Wolfgang Hartmann, Sareetha Kailayangiri. Ganglioside SSEA4 in Ewing sarcoma: A marker of tumor cells with highly aggressive features and a potential immune target. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4068.

Establishing a Disease-in-a-Dish Model to Study SARS-CoV-2 Infection During Prenatal Development.

Mother-to-fetus transmission of the SARS-CoV-2 virus via the placenta has been reported but cannot readily be studied in pregnant women. This protocol describes an in vitro method to investigate SARS-CoV-2 infection of human embryonic stem cells (hESCs), which are similar to epiblast cells in young postimplantation embryos. First, SARS-CoV-2 viral pseudoparticles, which contain the spike protein and a fluorescent reporter, are incorporated into a lentivirus backbone that is expanded in HEK 293T cells. Then, an infection assay based on hESCs is used with the viral pseudoparticles. An application of the infection assay in therapeutic drug screening is provided. This protocol allows infection of hESCs by SARS-CoV-2 pseudoparticles to be studied in vitro and can be used in conjunction with other assays to understand and potentially prevent infection. hESCs could also be differentiated to study infection in the three germ layers and their fetal cell derivatives. This disease-in-a-dish model could be readily applied to other hESC lines, and to other viral infections, that affect human prenatal development. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Preparing HEK 293T cells for lentiviral vector transfection Support Protocol 1: Visual inspection of transfected HEK 293T cells Basic Protocol 2: Generating viral pseudoparticles Support Protocol 2: Determining viral titer with HEK 293T-ACE2 cells Basic Protocol 3: Plating hESCs for the infection assay Support Protocol 3: Evaluating transduction efficiency.

Resetting histone modifications during human prenatal germline development

Histone modifications play critical roles in regulating gene expression and present dynamic changes during early embryo development. However, how they are reprogrammed during human prenatal germline development has not yet been elucidated. Here, we map the genome-wide profiles of three key histone modifications in human primordial germ cells (hPGCs) from weeks 8 to 23 of gestation for the first time by performing ULI-NChIP-seq. Notably, H3K4me3 exhibits a canonical promoter-enriched pattern, though with relatively lower enrichment, and is positively correlated with gene expression in globally hypomethylated hPGCs. In addition, H3K27me3 presents very low enrichment but plays an important role in not only dynamically governing specific bivalent promoters but also impeding complete X chromosome reactivation in female hPGCs. Given the activation effects of both global DNA demethylation and H3K4me3 signals, repressive H3K9me3 and H3K27me3 marks are jointly responsible for the paradoxical regulation of demethylation-resistant regions in hPGCs. Collectively, our results provide a unique roadmap of three core histone modifications during hPGC development, which helps to elucidate the architecture of germ cell reprogramming in an extremely hypomethylated DNA environment.

Современные тенденции картирования головного мозга

Brain atlases are widely used to determine relative location, form, and a number of other parameters of certain brain structures. Such data are required in medical practice, fundamental neuroscience research, and educating graduate and postgraduate medical students. Many papers observed the development of human brain atlases. However, recently numerous new atlases have been published, both digital and online ones. This tendency was triggered by intensive development and growing accessibility of modern visualization tools and digitizing novel data and existing archives. This study aimed to overview the historical background of and modern tendencies in the brain atlas development for Russian readers. Furthermore, foreign literature does not focus on Russian neurological tradition, so we attempted to cover this issue as well. Particular attention is paid to the atlases of human brain development. Keywords: human brain atlas, human prenatal development

1452-P: PDX1 and CKas Markers of Cell Maturation in the Human Pancreas

Regeneration of beta-cell mass is one of the fundamental problems in diabetology. Embryonic source of all pancreatic cell types is the epithelial cells of the primitive ducts. During pancreas development, epithelial progenitors differentiate in three directions, which is accompanied by changes in cell phenotype, including the expression of various types of cytokeratins, transcription factors, as well as hormones and some other antigens. The early markers of pancreatic epithelial progenitors are the homeodomain transcription factor Pdx 1 (pancreatic and duodenal homeobox 1) and an intermediate filament protein cytokeratin (CK19) . The aim of our work was to analyze the distribution of Pdx1 and CKduring endocrine pancreas development in humans. The study was performed on the pancreatic samples from 27 fetuses (gestational age 14-40 weeks) using double and triple immunohistochemistry with antibodies to Pdx1, CK19, and insulin or glucagon. During human prenatal development, the co-expression of CKand Pdx1 was detected in several cell types. Firstly, it was observed in the epithelial cells of the pancreatic ducts. During the branching of pancreatic ducts, CKexpression decreased in outgrows, while the Pdx1 expression was lowered in large ducts. Secondly, co-expression of CKand Pdx1 was detected in endocrine cells (mainly in alpha) . However, the intensity of the reaction to both markers in these cells was low. Phenotype of beta cells was Pdx1+/ CK19−. At the same time, during development, some cells with an intense reaction to CKand Pdx1 were detected in the forming islets. Apparently, an intense reaction to CK19/Pdx1 may characterized low-differentiated (progenitor) cells that are present in the epithelium of ducts and in the forming islets during the development of the human pancreas. Disclosure A.Proshchina: n/a. Y.Krivova: None. D.Otlyga: None. S.Saveliev: None.

The role of fetal programming in human carcinogenesis - May the Barker hypothesis explain interindividual variability in susceptibility to cancer insurgence and progression?

The growing incidence of cancers is pushing oncologists to find out new explanations other than the somatic mutation theory, based on the accumulation of DNA mutations. In particular, the embryo-fetal exposure to an increasing number of environmental factors during gestation might represent a trigger able to influence the susceptibility of the newborn to develop cancer later in life. This idea agrees with the fetal programming theory, also known as the Barker hypothesis. Here the role of insulin-like growth factors, thymosin beta-4, and epigenome are discussed as mediators of cancer in prenatal human development. The role of epigenetic factors that during gestation increase the predisposition to develop cancer and the similarities in the gene expression (like MMP9, OPN, TP53 and CDKN2A) between embryonic development and cancer are key factors. Likewise, maternal obesity might be able to re-program embryo-fetal development with long-term changes, including an increased risk to develop neuroblastoma and acute leukemia. Birth weight alone and birth weight corrected for gestational age are proposed as important variables capable of predicting the vulnerability to develop cancers. According to the findings here reported, we hypothesize that cancer prevention should start during gestation by improving the quality of maternal diet. In conclusion, the Barker hypothesis should be applied to cancer as well. Therefore, the identification of the epigenetic factors of cancer appears mandatory, so that the cancer prevention might start in the womb before birth.

Features of Blood Supply to the Bones of the Lower Leg in the Ankle Joint Region

The purpose of the study was to investigate the topography of permeable (nutrition) arteries in the lower third of leg during human ontogenesis. Materials and methods. The research was conducted on 30 specimens of human prefetuses and fetuses aged 3-9 months of prenatal development; 28 bone specimens of adult tibia and fibula and 27 series of computerized tomography scans of lower extremities of adults aged 21-72 were used. We have used a complex of methods for morphological research: anthropometry, morphometry, macromicroscopy, injections of blood vessels of X-ray contrasting mixtures, three-dimensional reconstruction and statistical analysis. Results and discussion. Cartilage osteogenesis occurs in the prefetal period of prenatal human development, in which blood vessels play a crucial morphofunctional role. During endochondral ossification of the tibia, the vessels of the bone cuff grow into the diaphysis of the cartilaginous model of the bone and osteogenic cells go beyond their limits. In the third trimester of prenatal development, blood vessels grow into the epiphyseal part of the cartilaginous model and an epiphyseal centre of ossification forms. Between the epiphysis and diaphysis centers of ossification, a metaphysical growth plate forms that develops intraosseous anastomosis between the diaphyseal and metaphysical blood vessels. In the metaphysis region, there are extra-skeletal anastomoses. Often, the insertion of nutrition arteries into the bone of the tibia is usually the middle third of bones (55%) and distal metaphysis (37%). In 10%, there were nutrition foramina in the upper third of the tibia. Three-dimensional reconstruction also clearly shows a more extensive and developed network of vessels in the bone marrow canal in metaphysical regions. In the middle third of the tibia and fibula, 1-3 nutrient foramina can be traced on most specimens. On the fibular, in addition to the posterior-medial localization of the nutrient arteries, there were variants with a "high" (above the metaphysis) placement of the entrance of the vessel into the bone substance. Conclusion. The most common places where arteries enter the bones of the lower leg are the middle third of the bones (55%) and the distal metaphysis (37%). In 10%, there were nutrient foramina in the upper third of the tibia. The three-dimensional reconstruction also clearly shows a more extensive and developed network of vessels in the bone marrow canal in metaphysical regions. During the postnatal period, we most often encountered the localization of nutritional arteries on the anterior-lateral surface of the tibia (23%), or their combination – the presence of both nutrient arteries on the posterior and medial bone surfaces (18.3%)

Occupational exposure to hexavalent chromium. Part I. Hazard assessment of non-cancer health effects

Hexavalent chromium (Cr(VI)) compounds have been studied extensively and several agencies have described their toxicological profile. In the past, personnel of the Dutch Ministry of Defence may have been exposed to Cr(VI) during maintenance activities. To investigate if this exposure may have caused irreversible adverse health effects, the Dutch National Institute for Public Health and the Environment (RIVM) summarized all available knowledge from previous evaluations. This information was complemented with a scoping review to retrieve new scientific literature. All scientific evidence was evaluated in workshops with external experts to come to an overview of irreversible adverse health effects that could be caused by occupational exposure to Cr(VI) compounds. This review focuses on non-cancer health effects.It was concluded that occupational exposure to Cr(VI) can cause perforation of the nasal septum by chromium ulcers, chronic lung diseases, including asthma, rhinitis, pulmonary fibrosis and COPD, skin ulcers and allergic contact dermatitis in humans. It is currently insufficiently clear if Cr(VI) can cause irreversible diseases due to disturbances of the immune system (other than allergic contact eczema, allergic asthma and rhinitis and chronic lung diseases) or adverse effects on fertility or prenatal development in humans.

Epigenetic clocks reveal a rejuvenation event during embryogenesis followed by aging.

The notion that the germ line does not age goes back to the 19th-century ideas of August Weismann. However, being metabolically active, the germ line accumulates damage and other changes over time, i.e., it ages. For new life to begin in the same young state, the germ line must be rejuvenated in the offspring. Here, we developed a multi-tissue epigenetic clock and applied it, together with other aging clocks, to track changes in biological age during mouse and human prenatal development. This analysis revealed a significant decrease in biological age, i.e., rejuvenation, during early stages of embryogenesis, followed by an increase in later stages. We further found that pluripotent stem cells do not age even after extensive passaging and that the examined epigenetic age dynamics is conserved across species. Overall, this study uncovers a natural rejuvenation event during embryogenesis and suggests that the minimal biological age (ground zero) marks the beginning of organismal aging.