Human Prenatal Development Research Articles

Time-dependent expression of cytochrome p450 epoxygenases during human prenatal development

There is growing evidence that some members of cytochrome P450 enzymes contribute to regulation of normal prenatal development. CYP epoxygenases (CYP2C and CYP2J subfamilies) convert arachidonic acid into four regioisomeric epoxyeicosatrienoic acids (EETs), biologically active molecules involved in mitogenesis and cell signaling. Almost nothing is known about localization of their expression in tissues during human prenatal development. The spatio-temporal expression pattern of CYP2C8, CYP2C9, CYP2C19 and CYP2J2 in human embryonic/fetal intestines, liver, and kidney was investigated by immunohistochemical method. CYP epoxygenases are expressed already in early stages of development in these embryonic/fetal tissues (as early as 7th week of IUD in the intestines, 5th week of IUD in the liver, and 6th week of IUD in the kidney). In kidney, CYP epoxygenases are expressed in the metanephrogenic blastema (but not in the uninduced mesenchyme) and in the tubular system. In the intestines, diverse CYP epoxygenases distribution along crypt-villus axis could suggest role in cell differentiation. Moreover, we detected higher CYP2J2 level in these organs than in adult tissue samples.

Desafios atuais da pesquisa em toxicologia: Avaliação da toxicidade de nanomateriais manufaturados para o desenvolvimento

Nanomaterials are particles or fibers with at least one of the three dimensions in the size range between 1 and 100 nm. Owing to unique physical and chemical properties, nano-sized particles (NPs) have a variety of industrial uses and are more and more prevalent in everyday life. However, despite the growing number of nanotechnology products, health risk assessment of NPs is in its early infancy. The potential adverse effects of NPs on prenatal development are even less well investigated. This article summarizes the literature on the developmental toxicity of NPs. Generally, the studies are very recent and include ex vivo experiments using non-mammalian species, in vitro assays (mouse embryonic stem cell test) and in vivo investigations using rodents. Very little has been published on the effects of NPs on the development and function of the human placenta or on the transference of NPs into the human embryo and fetus. Some limitations of using ex vivo and in vitro assays to predict adverse effects of NPs on human prenatal development are discussed in this overview. The structural and functional differences between the rodent and human placenta in early pregnancy and their possible relevance to the transplacental passage of NPs are also commented upon.

Current challenges in toxicological research: Evaluation of the developmental toxicity of manufactured nanomaterials

Nanomaterials are particles or fibers with at least one of the three dimensions in the size range between 1 and 100 nm. Owing to unique physical and chemical properties, nano-sized particles (NPs) have a variety of industrial uses and are more and more prevalent in everyday life. However, despite the growing number of nanotechnology products, health risk assessment of NPs is in its early infancy. The potential adverse effects of NPs on prenatal development are even less well investigated. This article summarizes the literature on the developmental toxicity of NPs. Generally, the studies are very recent and include ex vivo experiments using non-mammalian species, in vitro assays (mouse embryonic stem cell test) and in vivo investigations using rodents. Very little has been published on the effects of NPs on the development and function of the human placenta or on the transference of NPs into the human embryo and fetus. Some limitations of using ex vivo and in vitro assays to predict adverse effects of NPs on human prenatal development are discussed in this overview. The structural and functional differences between the rodent and human placenta in early pregnancy and their possible relevance to the transplacental passage of NPs are also commented upon.

The developmental origins of laterality: Fetal handedness

This paper reviews the evidence for lateralized motor behavior in the fetus around a number of key questions: does the fetus exhibit signs of laterality? when does lateralized motor behavior begin? is the lateralized preference consistently displayed? does prenatal handedness relate to postnatal handedness? and, does prenatal handedness relate to brain functioning? The evidence indicates that the fetus exhibits lateralized behavior from 10 weeks gestation, as soon as it independently moves its arms, and this is the precursor of lateralized motor behavior observed post-natally. Data is presented suggesting that the strength of laterality decreases with advancing gestation and this correlates with more efficient information processing as assessed by habituation. However extreme caution is warranted in attempting to link asymmetric motor behavior and brain function prenatally. The paper concludes that the initial developmental emergence of lateralized behavior is under genetic control and is a fundamental feature of prenatal human development.

Diversification and conservation of the extraembryonic tissues in mediating nutrient uptake during amniote development

The transfer of nutrients from the mother through the chorioallantoic placenta meets the nutritional needs of the embryo during human prenatal development. Although all amniotes start with a similar “tool kit” of extraembryonic tissues, an enormous diversity of extraembryonic tissue formation has evolved to accommodate embryological and physiological constraints unique to their developmental programs. A comparative knowledge of these extraembryonic tissues and their role in nutrient uptake during development is required to fully appreciate the adaptive changes in placental mammals. Here, we offer a comparative embryological perspective and propose that there are three conserved nutrient transfer routes among the amniotes. We highlight the importance of the yolk sac endoderm, thought to be a vestigial remnant of our amniote lineage, in mediating nutrient uptake during early human development. We also draw attention to the similarity between yolk sac endoderm-mediated and trophectoderm-mediated nutrient uptake.

A method for rapid dose–response screening of environmental chemicals using human embryonic stem cells

IntroductionHuman embryonic stem cells (hESC) provide an invaluable model for assessing the effects of environmental chemicals and drugs on human prenatal development. However, hESC are difficult to adapt to 96-well plate screening assays, because they survive best when plated as colonies, which are difficult to count and plate accurately. The purpose of this study is to present an experimental method and analysis procedure to accomplish reliable screening of toxicants using hESC. MethodsWe present a method developed to rapidly and easily determine the number of cells in small colonies of hESC spectrophotometerically and then accurately dispense equivalent numbers of cells in 96-well plates. The MTT assay was used to evaluate plating accuracy, and the method was tested using known toxicants. ResultsThe quality of the plate set-up and analysis procedure was evaluated with NIH plate validation and assessment software. All statistical parameters measured by the software were acceptable, and no drift or edge effects were observed. The 96-well plate MTT assay with hESC was tested by performing a dose–response screen of commercial products, which contain a variety of chemicals. The screen was done using single wells/dose, and the reliability of this method was demonstrated in a subsequent screen of the same products repeated three times. The single and triple screens were in good agreement, and NOAELs and IC50s could be determined from the single screen. The effects of vapor from volatile chemicals were studied, and methods to monitor and avoid vapor effects were incorporated into the assay. DiscussionOur method overcomes the difficulty of using hESC for reliable quantitative 96-well plate assays. It enables rapid dose–response screening using equipment that is commonly available in laboratories that culture hESC. This method could have a broad application in studies of environmental chemicals and drugs using hESC as models of prenatal development.

Advances in the Study of Fetal Development: From Descriptive to Dynamic Embryology

ABSTRACT Remarkable advances in medical imaging are facilitating the morphological study of early human prenatal development as well as the clinical assessment of normal and abnormal development during gestation. Classical descriptive embryology has been transformed into dynamic embryology and the interaction between basic embryology and clinical medicine is becoming more and more intimate. This paper describes an overview of the advances in the study of human embryonic and fetal development with special emphasis on the recent progress in embryo imaging. How to cite this article Shiota K. Advances in the Study of Fetal Development–From Descriptive to Dynamic Embryology. Donald School J Ultrasound Obstet Gynecol 2012;6(2):171-178.

Phenotype-specific adverse effects of XPD mutations on human prenatal development implicate impairment of TFIIH-mediated functions in placenta

Mutations in XPD (ERCC2), XPB (ERCC3), and TTD-A (GTF2H5), genes involved in nucleotide excision repair and transcription, can cause several disorders including trichothiodystrophy (TTD) and xeroderma pigmentosum (XP). In this study, we tested the hypothesis that mutations in the XPD gene affect placental development in a phenotype-specific manner. To test our hypothesis and decipher potential biologic mechanisms, we compared all XPD-associated TTD (n=43) and XP (n=37) cases reported in the literature with respect to frequencies of gestational complications. Our genetic epidemiologic investigations of TTD and XP revealed that the exact genetic abnormality was relevant to the mechanism leading to gestational complications such as preeclampsia. Through structural mapping, we localized the preeclampsia-associated mutations to a C-terminal motif and the helicase surfaces of XPD, most likely affecting XPD's binding to cdk-activating kinase (CAK) and p44 subunits of transcription factor (TF) IIH. Our results suggested a link between TTD- but not XP-associated XPD mutations, placental maldevelopment and risk of pregnancy complications, possibly due to impairment of TFIIH-mediated functions in placenta. Our findings highlight the importance of the fetal genotype in development of gestational complications, such as preeclampsia. Therefore, future studies of genetic associations of preeclampsia and other placental vascular complications may benefit from focusing on genetic variants within the fetal DNA.

The effect of cigarette smoke on fertilization and pre-implantation development: assessment using animal models, clinical data, and stem cells.

Numerous studies have repeatedly shown that women who smoke experience problems establishing and maintaining pregnancies, and recent work has further demonstrated that the in utero effects of smoke may not be manifested until months or even years after birth. The purpose of this review is to examine the recent literature dealing with the effects of cigarette smoke on the earliest stages of human prenatal development. Studies in this area have included the use of animal models, patients undergoing in vitro fertilization, and embryonic stem cell models. Events leading to fertilization, such as cumulus expansion, hyperactivation of sperm motility, and oocyte pick-up by the oviduct are all impaired by smoke exposure in animal models. Steps crucial to fertilization such as the acrosome reaction and sperm binding to the zona pellucida are likewise inhibited by cigarette smoke. Preimplantation embryos and stem cells that model embryos show a number of adverse responses to smoke exposure, including poor adhesion to extracellular matrices, diminished survival and proliferation, and increased apoptosis. The current literature demonstrates that the earliest stages of prenatal development are sensitive to smoke exposure and indicates that pregnant women should be advised not to smoke during this time.

Editorial: [Somatic Genome Variations: First Steps towards a Deeper Understanding of an Underappreciated Source of Biodiversity and Disease (Guest Editors: Y.B. Yurov and I.Y. Iourov)

Editorial: [Somatic Genome Variations: First Steps towards a Deeper Understanding of an Underappreciated Source of Biodiversity and Disease (Guest Editors: Y.B. Yurov and I.Y. Iourov)

Somatic genomic variations in early human prenatal development.

Only 25 to 30% of conceptions result in a live birth. There is mounting evidence that the cause for this low fecundity is an extremely high incidence of chromosomal rearrangements occurring in the cleavage stage embryo. In this review, we gather all recent evidence for an extraordinary degree of mosaicisms in early embryogenesis. The presence of the rearrangements seen in the cleavage stage embryos can explain the origins of the placental mosaicisms seen during chorion villi sampling as well as the chromosomal anomalies seen in early miscarriages. Whereas these rearrangements often lead to implantation failure and early miscarriages, natural selection of the fittest cells in the embryo is the likely mechanism leading to healthy fetuses.

An atlas of prenatal development of the human orofacial region

There are several atlases available showing prenatal human development. However, none is focused on prenatal orofacial development during maxillary and mandibular bone formation. These events, together with dental development and formation of the temporomandibular joint, take place during several fetal stages. While photographic atlases are limited to depicting the outer shape, and atlases based on histological sections only show a series of single sections, an atlas based on three-dimensional reconstructions from serial sections can show both the outer skin and the structures underneath, which can be electronically dissected layer by layer. In this Focus article, we present our atlas on prenatal human orofacial development, which is accessible online at the Journal's website.

Relationship between urokinase plasminogen activator receptor (uPAR) and the invasion of human prenatal hair follicle

During the morphogenesis of hair follicles, the invasive migration of basal keratinocytes resembles cell's dissemination of tissue remodeling. The urokinase-type plasminogen activator receptor (uPAR) appears to be a key molecule in the metastasis. In order to elucidate the relationship between uPAR and the invasion of the human hair follicle, immunohistochemistry, RT-PCR, plasmids transfection, and western blot were used. The results showed that uPAR was expressed in the outermost epithelial cells of the hair follicle and the basal keratinocytes of epidermis, and that the expression decreased with the development of the hair follicle. The cells of the outer root sheath (ORS) and interfollicle epidermis, which overexpressed uPAR, acquired increased invasiveness; however, they showed decreased invasion with overexpression of the urokinase-type plasminogen activator amino terminal fragment (uPA ATF), which inhibited the combination of uPAR and uPA competitively, and the cell invasive migration with overexpressed uPAR was required activated extracellular signal-regulated kinases (ERK). These results implied that overexpression of uPAR promote the invasive migration of hair follicle into the dermis in uPA-dependent and independent manner during human prenatal development.

Insights into the Regulation of a Common Variant of HMGA2 Associated with Human Height During Embryonic Development

Early genetic studies in the mouse and chicken identified the HMGA oncogene as a candidate that regulates body height. Subsequent genome-wide SNP studies revealed a significant association of rs1042725 genotypes CT and CC in the 3' UTR of HMGA2 with human height. Together, these studies indicated that HMGA2 expression levels during prenatal development might be a critical factor that contributes to the height phenotype. In the present study, we sought to gain insight into the regulation of HMGA2 during human embryonic development and provide evidence that the rs1042725 genotype is unlikely to affect HMGA2 levels in pluripotent human embryonic stem cells (hESCs). This implies that hESCs in the inner cell mass of blastocysts are most likely not involved in determining the human height phenotype associated with this SNP. By applying a computational approach and cell-based reporter assays, we then identified miR-196b as a candidate microRNA that could contribute to SNP-specific expression of HMGA2 during human prenatal development. We briefly discuss this result in the context of other known functions for miR-196b during vertebrate development.

Etoposide induces MLL rearrangements and other chromosomal abnormalities in human embryonic stem cells

MLL rearrangements are hallmark genetic abnormalities in infant leukemia known to arise in utero. They can be induced during human prenatal development upon exposure to etoposide. We also hypothesize that chronic exposure to etoposide might render cells more susceptible to other genomic insults. Here, for the first time, human embryonic stem cells (hESCs) were used as a model to test the effects of etoposide on human early embryonic development. We addressed whether: (i) low doses of etoposide promote MLL rearrangements in hESCs and hESCs-derived hematopoietic cells; (ii) MLL rearrangements are sufficient to confer hESCs with a selective growth advantage and (iii) continuous exposure to low doses of etoposide induces hESCs to acquire other chromosomal abnormalities. In contrast to cord blood-derived CD34(+) and hESC-derived hematopoietic cells, exposure of undifferentiated hESCs to a single low dose of etoposide induced a pronounced cell death. Etoposide induced MLL rearrangements in hESCs and their hematopoietic derivatives. After long-term culture, the proportion of hESCs harboring MLL rearrangements diminished and neither cell cycle variations nor genomic abnormalities were observed in the etoposide-treated hESCs, suggesting that MLL rearrangements are insufficient to confer hESCs with a selective proliferation/survival advantage. However, continuous exposure to etoposide induced MLL breaks and primed hESCs to acquire other major karyotypic abnormalities. These data show that chronic exposure of developmentally early stem cells to etoposide induces MLL rearrangements and make hESCs more prone to acquire other chromosomal abnormalities than postnatal CD34(+) cells, linking embryonic genotoxic exposure to genomic instability.

ENDOCRINE DISRUPTION: Developmental Picture Window

The concept of endocrine disruption emerged in the early 1990s with the observation that natural and industrial compounds were interfering with sex hormone signaling, thereby adversely affecting male and female reproductive health. Since then, many endocrine-disrupting chemicals (EDCs) have been identified, and the field now comprises thousands of studies encompassing virtually every system in the body. On 10 February 2009, the Paonia, Colorado–based nonprofit group The Endocrine Disruption Exchange (TEDX) unveiled the Critical Windows of Development timeline (http://www.criticalwindows.com). The timeline provides a snapshot of the state of the science of when organs and systems develop, when they are vulnerable to particular EDC exposures, and what effects have been observed. Endocrine disruption is not confined to the reproductive system because virtually every system in the body is hormonally responsive. The effects can differ depending on when exposure occurred. For example, according to the timeline, prenatal exposure in mice to bisphenol A (BPA) at gestational days 11.5–18.5 is associated with abnormal fetal egg cell development whereas exposure at gestational days 15–18 is associated with structural changes to the vagina. Theo Colborn, president of TEDX, first conceptualized condensing the body of EDC literature into a user-friendly graphic format. Despite Colborn’s optimism concerning the timeline’s feasibility, it took several years to figure out how to present the data visually. “We had the data here, and we had everything in boxes, but displaying it in the picture we wanted to create was complex,” says Colborn. An early attempt involved an extraordinary expanse of butcher paper; a collaboration with Carol Kwiatkowski, now executive director of TEDX, helped bring Colborn’s vision to fruition. “As far as we know, there’s nothing out there like it,” says Kwiatkowski, who organized and then funneled the research into a database before finding the web developer who could translate it into the desired visual display. The display comprises a series of horizontal bars, each depicting a specific system or organ for the full 38 weeks of human pregnancy. Corresponding time points in rodent development are indicated along the top of the screen. Tick marks along the bars indicate studies done at specific time points corresponding to points in normal human development. Another series of tick marks indicates EDC studies performed in the laboratory. Clicking on a mark brings up a concise summary of the study details with a link to the PubMed record. All chemical studies notated on the timeline must be original research using rodent or human cells or tissues. Exposures of parts per million or less to an EDC must have occurred during a time point equivalent to some point in human pre-natal development. “We wanted to keep it within a range [representing the point] where we know from the literature on ambient exposures and monitoring studies that humans might be exposed,” says Colborn. The timeline is currently populated with all existing BPA studies that meet the criteria for inclusion; staff are still plotting dioxin and phthalate studies. New studies will be inserted upon publication, and more chemicals will be incorporated into the timeline in the coming year. The timeline, which is free to all users, fills several needs at once. “One of the needs that has become apparent over the years has been just a basic reference for normal development in both humans and rodent models,” says Kris Thayer, a health science administrator at the NIEHS. To begin to grasp how various systems are affected by endocrine disruption, it is necessary to know when those systems are developing. “What Theo has done is to develop a graphic tool—it’s very visual, very interactive, and very well referenced—so you can easily see everything in one place,” says Thayer. Jerry Heindel, a scientific program administrator at the NIEHS, says the time-line could be useful in determining areas where research is needed and how to plan new studies. “Even a cursory examination of the tick marks that show when experiments have been done provides a nice overview of the timing of studies throughout development,” he says. “This information can then be used to refine the timing, doses, and end points of future studies.” Colborn also hopes the timeline will inspire scientists to take a broader view of endocrine disruption and possibly promote collaboration across systems. Researchers tend to focus on one system or organ at a time, she says, and as a result a lot of information that could be gleaned from carefully controlled experiments is never gathered. “I think the timeline will be very useful for researchers [from many disciplines], especially as people cut across different biological systems,” says Thayer. “The information on the timeline is contained in reference books and research journals, but it’s very handy to have it all in one place.”

Pubertal development in children and adolescents born after IVF and spontaneous conception

Previous studies demonstrated a link between adverse conditions during prenatal life and the development of diseases in adult life. It is still unclear whether IVF conception could permanently affect early prenatal development in humans, with post-natal health consequences. The objective of the present study is to examine pubertal development in 8-18-year-old IVF singletons and controls born from subfertile parents who attended one Dutch fertility clinic were included. IVF singletons and controls born from subfertile parents who attended one clinic in the Dutch OMEGA study were included. Pubertal stage by Tanner's classification, age at menarche and menstrual cycle characteristics were studied in the total population (n = 233: 115 IVF-conceived boys and 118 IVF-conceived girls, each with age-matched comparison groups). Bone age and sex hormone levels were examined in two distinct pubertal subpopulations. Pubertal stage and age at menarche were not significantly different between IVF and control children. In the pubertal subpopulation, a higher bone age-chronological age (BA-CA) ratio and a larger BA-CA difference were observed in IVF-conceived girls compared with controls (1.04 +/- 0.07 versus 1.02 +/- 0.08, P = 0.022; 0.54 +/- 0.82 versus 0.18 +/- 1.00 year, P = 0.021, respectively). Furthermore, dehydroepiandrosterone sulphate (DHEAS) and LH levels were significantly higher in IVF-conceived girls than in control subjects (2.5 versus 1.9 micromol/l, P = 0.017, and 1.5 versus 0.6 U/l, P = 0.031, respectively). Bone age appeared to be advanced in pubertal IVF-conceived girls, but not in boys, compared with controls. Increased DHEAS and LH concentrations were found among IVF girls.

What Do Sex, Twins, Spotted Hyenas, ADHD, and Sexual Orientation Have in Common?

The otoacoustic emissions (OAEs) measured in a collection of special populations of humans and certain nonhuman species suggest that OAEs may provide a window into some processes of human prenatal development and sexual differentiation. For reasons that are unclear, OAEs appear to be highly sensitive to events occurring during prenatal development that seem to be related to the degree of exposure to androgens a fetus receives. The (largely circumstantial) evidence for a relationship between androgen exposure and OAE strength comes from a series of studies of twins, children with attention-deficit/hyperactivity disorder, people of differing sexual orientations, and spotted hyenas, among others. Some conclusions are bolstered by parallel studies using auditory evoked potentials (AEPs). OAEs and AEPs are simple, objective, noninvasive measures that appear to have potential as tools of value to researchers working on a wide variety of basic and applied topics beyond audition.

Observations on the Prenatal Development of Human Lymphatic Vessels with Focus on Basic Structural Elements of Lymph Flow

The prenatal development of human lymphatic systems has not attracted enough attention by lymphatic researchers in the past. Yet clearly these critical, early events determine the fate and function of the human lymphatic system. The main focus of these studies was to investigate the embryonic development of human lymphangions including lymphatic valves and muscle cells, to better understand the prenatal formation of basic structural elements of lymph flow. This review in most of its parts is a short summary of the findings. It provides important information necessary for understanding the development and functioning of the human lymphatic system. The structural basis of the active lymph transport system--the lymphatic muscle cells and lymphatic valves--which is absolutely necessary for all functions of lymphatic system, is already formed during the first half of the prenatal development in humans. During the second half of this development maturation of this system is already underway. The enlargement of lymphatic muscle cells together with increases in their quantity leads to formation of the multi-layered lymphatic vessel wall, able to develop contractions strong enough to propel lymph downstream of the lymphatic channels against gravity in bipedal humans. The development of the competent valves in lymphatic vessels occurs at the same time creating the ground for effective net, unidirectional lymph flow. The data summarized here represents some of the first systematic studies of the prenatal development of lymphatic muscle cells and valves in humans.

Key Developments in Endocrine Disrupter Research and Human Health

Environmental etiologies involving exposures to chemicals that mimic endogenous hormones are proposed for a number of adverse human health effects, including infertility, abnormal prenatal and childhood development, and reproductive cancers (National Research Council, 1999; World Health Organization, 2002). Endocrine disrupters represent a significant area of environmental research with important implications for human health. This article provides an overview of some of the key developments in this field that may enhance our ability to assess the human health risks posed by exposure to endocrine disrupters. Advances in methodologies of hazard identification (toxicogenomics, transcriptomics, proteomics, metabolomics, bioinformatics) are discussed, as well as epigenetics and emerging biological endpoints.