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PubMed1996

Embryonic and early fetal development of human taste buds: a transmission electron microscopical study.

BACKGROUND: Taste buds are assemblies of slender epithelial cells that receive chemical stimuli from the outer (oral) environment. In contrast to the large and well documented information on the morphology of taste buds in adult humans and animals, there are only a few reports on fetal ones, and ultrastructural studies of prenatal human taste buds are lacking completely. Therefore, the present investigation has been carried out to study the taste bud primordium, its morphological changes including synaptogenesis, cell differentiation, and taste pore formation from the time of the onset of taste bud formation around the 8th week until the 15th postovulatory week. METHODS: Taste bud primordia of 42 human embryonic/fetal tongues have been examined by means of transmission electron microscopy. RESULTS: Nerve fibers approach the lingual epithelium between the 6th and 7th postovulatory week. They penetrate the basal lamina during the 8th week and form synapses with poorly differentiated, elongated, epithelial cells. By the 12th week, more differentiated cell types are seen: 1) electron-dense cells resembling type III cells of the adult taste bud containing large numbers of dense-cored vesicles (80-150 nm in diameter); 2) electron-dark cells with well developed endoplasmic reticulum and many apical mitochondria, being candidates for type II cells. Basally, these cells have foot-like processes containing dense-cored vesicles (120-200 nm in diameter), but they do not synapse to nerve fibers. Type I cells, characterized by apically located dense secretory granules, are not observed. First shallow grooves above the taste bud primordium are found around the 10th week. Untypically differentiated apical cellular processes extend onto the surface. Most of the taste pores develop around the 14th to 15th week. In the taste pit, mucous material is not present during the first 15 weeks of gestation. Synapses between cells and afferent nerve fibers were found by the 8th week, reaching a maximum around the 12th to 13th week. CONCLUSIONS: The early presence of taste bud cells containing dense-cored vesicles suggests an at least dual function of embryonic/ fetal taste buds: First, from the 8th until the 14th week, non-gustatory, paracrine functions should be considered. After the 14th week of gestation, when typical taste pores are present, the taste buds possibly start their gustatory function. Differentiated marginal cells are possibly involved in the formation of the taste pore. The lack of type I cells producing the mucous material in the taste pit indicates that the taste bud has not achieved a fully developed function until the 15th week of gestation.

Aging↗
PubMed1994

Expression of type II collagen at the middle stages of chick embryonic and human fetal skin development.

Using in situ hybridization techniques and RNase protection assays, type II collagen mRNA was transiently detected in the epidermis of chick embryonic skins during days 9-15 after fertilization, with a maximum expression at day 11. Immunohistochemical studies demonstrated that deposition of type II collagen was also transiently localized at the subepidermal region during days 10-15. Type II collagen gene and gene product concomitantly started to decline preferentially at the region where feather buds were being formed on day 12, and thereafter diminished at the region between feather buds. Using immunohistochemical methods, type II collagen was also detected in human fetal scalp skin at 17-23 fetal weeks at the subepidermal region, excluding the region beneath the hair follicles. These results indicate that the lack of type II collagen expression is related to the development of feather and hair at a certain stage of chick embryonic and human fetal skin development.

Animals↗
PubMed1995

Developmental toxicity and structure-activity relationships of chlorophenols using human embryonic palatal mesenchymal cells.

The chlorophenols (CPs) comprise a major class of widely distributed and frequently occurring environmental contaminants. Previous studies have demonstrated the adverse effects of CPs on embryonic and fetal development. HEPM (human embryonic palatal mesenchymal) and MOT (mouse ovarian tumor) cell lines have been utilized in complementary bioassays for the detection of teratogens, but not the CPs. In this study, our objectives were 2-fold: (1) to determine if the HEPM assay could be used to complement other bioassay systems of nonhuman origin, i.e., Hydra attenuata (HA) and rat whole embryo culture (WEC), in the evaluation of the developmental toxicity of CPs, and (2) to delineate the ability of the HEPM assay to evaluate structure-activity relationships of pentachlorophenol (C5P), 2,3,4,5-tetrachlorophenol (C4P), 2,3,5-trichlorophenol (C3P), 3,5-dichlorophenol (C2P), 4-monochlorophenol (CP), phenol, and CP derivatives (i.e., acetates, sodium phenates and anisoles). HEPM cells were seeded into each well of a 24-well plate and cultivated for 24 h. The medium was replaced with fresh medium containing various concentrations of test chemicals dissolved in dimethyl sulfoxide (DMSO, 0.1%). After culturing for 72 h, the medium was removed, cells were trypsinized, and cell number determined. The HEPM cell growth inhibition assay demonstrated a linear relationship between the IC50 values of the CPs and degree of chlorine substitution. The IC50 values of C5P, C4P, C3P, C2P, CP, and phenol were 18.8, 21.5, 27.5, 63.0, 150.0 and 470.0 microM, respectively. A clear structure-activity relationship was observed between toxicity of CPs and the degree of chlorine substitution. The rank order of CP toxicity from the HEPM assay (i.e., C5P > C4P > C3P > C2P > CP > phenol) is in excellent agreement with previous in vitro and in vivo studies. However, contrary to published reports, the HEPM assay predicted that all CPs were teratogenic (false positives). These findings suggest that the HEPM cell growth inhibition bioassay may be useful to discriminate between subtle differences in structure-activity and, in combination with other bioassays, might facilitate the rapid detection and prioritization of diverse cytotoxins, including various developmental toxicants. Importantly, conclusions about the teratogenicity of a test chemical (via HEPM testing) should be approached with caution and confirmed with other teratogen-sensitive systems.

Animals↗
PubMed2000

Embryonic and early fetal development of the human neocortex.

Early corticogenesis was studied in human embryos and early fetuses from Carnegie stages 16 to 22 (5-8 gestational weeks) by using immunohistochemistry for Reelin (Reln), calretinin (CR), and glutamic acid decarboxylase (GAD). A first population of Reln-positive cells appears in the neocortical anlage at stage 16 and increases in number at stages 17-18. At stages 19-20, a monolayer of horizontal CR- and GAD-positive, Reln-negative neurons forms in the preplate, whereas Reln-positive cells shift into a subpial position. Another cell class, the pioneer projection neuron, is CR-positive but GAD- and Reln-negative; pioneer cells contribute early corticofugal axons. Pioneer cells first appear below the monolayer at stage 20 and form a pioneer plate at stage 21. The cortical plate (CP) proper emerges at stage 21 and inserts itself within the pioneer plate, which is thus split into a minor superficial component and a larger deep component that presumably corresponds to the subplate. Initial CP neurons are radially organized and mostly CR-negative. Reln-positive cells remain consistently segregated from the pioneer cells and are thus not directly involved in preplate partition. Our data indicate that the neuronal composition of the human neocortical preplate is more complex than generally described and that various neurons participate in a sequence of events that precede the emergence of the CP.

Calbindin 2↗
PubMed2002

Xenografted human whole embryonic and fetal entoblastic organs develop and become functional adult-like micro-organs.

BACKGROUND AND AIMS: The aim of this study was to study the morphological and functional development in vivo of whole human embryonic and fetal stomachs, intestines, tracheas, and lungs, which would otherwise be ethically and technically impossible to perform in utero, by microsurgically grafting these organs into nude mice. MATERIALS AND METHODS: Five hundred fifty-seven human organs obtained from legally aborted embryos and fetuses of 6-10 weeks were microsurgically grafted into nude mice for 1 to 273 days. Following different grafting times, biopsies were taken for optical and electron microscopy, in situ hybridization, and cellular kinetics studies. A catheter was introduced into the human organs in order to collect and analyze secretions. RESULTS: All of the grafts took successfully. Macroscopic growth was fast during the first 6 to 10 weeks, following which organ size was stable. In situ hybridization studies detected only a minute level of mouse mesenchymal chimerism in the grafts. The different epithelial cells differentiated, became of adult type, and remained normal during the remainder of the grafting periods. The pH of gastric juice from stomachs grafted for 10 to over 90 days dropped from 8.0 +/- 0.1 to 1.58 +/- 0.29 over this time period (P < 0.001), intrinsic factor levels were stable, and pepsin ranged from 6.8 +/- 7.8 to 134 +/- 51 units (P < 0.001). CONCLUSIONS: These results demonstrate that the development of entoblastic organs from human embryos and fetuses microsurgically grafted into nude mice is similar to that occurring in utero. As such, this method provides a model for the analysis of whole human organs in development and later normal adult-like micro-organs for physiological, therapeutic, and pathological studies.

Animals↗
PubMed2006

Effect of culturing mouse embryos under different oxygen concentrations on subsequent fetal and placental development.

The oxygen concentration used during embryo culture can influence embryo development and quality. Reducing the oxygen concentration in the atmosphere to 2% during post-compaction culture of mouse embryos perturbs embryonic gene expression. This study examined the effect of culturing mouse embryos under different oxygen concentrations on subsequent fetal and placental development. Embryos were cultured from the zygote to morula stage under 7% oxygen, followed by 20, 7 or 2% oxygen to the blastocyst stage. Cultured and in vivo developed blastocysts were transferred into pseudopregnant recipients. Fetal and placental outcomes were analysed at day 18 of pregnancy. Implantation rate was not influenced by embryo culture conditions, but resorption rates were increased in embryos cultured under 2% oxygen, compared with 7% oxygen. Day 18 fetal weights were reduced following culture under 2%, compared with 7 or 20% oxygen, or in vivo development. Placental weight was not influenced by culture conditions. No differences in the proportion of junctional or labyrinthine exchange regions within the placenta or the morphometry of the labyrinthine region were detected. Surface density (surface area/gram labyrinth) of trophoblast available for exchange was reduced in placentas developed from embryos cultured under 2% oxygen, compared with 7% oxygen. Placental gene expression of Slc2a1, Slc2a3, Igf2, Igf2r and H19 was not influenced by oxygen conditions during embryo culture. Thus, exposure to 2% oxygen during post-compaction pre-implantation embryo development has adverse consequences for fetal development in the mouse. Oxygen is a significant component of the embryonic environment and reductions in oxygen availability can influence both embryonic gene expression and subsequent fetal development.

Aging↗
PubMed1998

Effects of low-frequency magnetic fields on fetal development in CBA/Ca mice.

Effects of alternating magnetic fields (MFs) on the embryonic and fetal development in CBA/Ca mice were studied. Mated females were exposed continuously to a sinusoidal 50 Hz (13 microT or 0.13 mT root mean square) or a sawtooth 20 kHz (15 microT peak-to-peak) MF from day 0 to day 18 of pregnancy for 24 h/day until necropsied on day 18. Control animals were kept under the same conditions without the MF. MFs did not cause maternal toxicity. No adverse effects were seen in maternal hematology and the frequency of micronuclei in maternal bone marrow erythrocytes did not change. The MFs did not increase the number of resorptions or fetuses with major or minor malformations in any exposure group. The mean number of implantations and living fetuses per litter were similar in all groups. The corrected weight gain (weight gain without uterine content) of dams, pregnancy rates, incidences of resorptions and late fetal deaths, and fetal body weights were similar in all groups. There was, however, a statistically significant increase in the incidence of fetuses with at least three skeletal variations in all groups exposed to MFs. In conclusion, the 50 Hz or 20 kHz MFs did not increase incidences of malformations or resorptions in CBA/Ca mice, but increased skeletal variations consistently in all exposure groups.

Animals↗
PubMed1989

Development of human embryonic and fetal dermal vasculature.

This report summarizes recent advances in the understanding of the structure and organization of the microvasculature in developing human skin. Previous observations suggested that the skin contains no blood vessels as late as eight weeks estimated gestational age (EGA). Computer reconstructions, in conjunction with light and transmission electron microscopy (TEM), however, demonstrated that specimens as young as 35-45 d show a level of vascular complexity previously unknown. The computer reconstructions showed that the vasculature was organized in one or two planes parallel to the epidermis. A simple, single plane was evident in specimens 40-50 d EGA, whereas specimens 50-75 d EGA showed two planes. Fewer vessels were continuous throughout the tissue sample in the younger specimens compared with the older specimens. Superior views highlighted the continuities and connections of vessels. The younger specimens showed more discontinuous segments of vessels when compared with the network established in the older specimens. In the earliest specimens examined morphologically (35-40 d), simple, capillarylike vessels were morphologically identifiable in presumptive dermis. The samples studied by TEM revealed detailed structure of the vessel wall including extreme attenuations and projections, plasmalemmal vesicles, and junctions similar to adult endothelial cells. Little or no basal lamina surrounded the vessel. The basal lamina first appeared in the form of amorphous deposits and eventually thickened and became continuous. By the end of the first trimester, the basal lamina still lacked the organization of adult cutaneous arterial and venous segments. These findings suggest that the major vascular organization of the dermis is defined in the first trimester of development.

Biomarkers↗
PubMed1999

The study of morphology and circulation of early embryo by three-dimensional ultrasound and power Doppler.

Three-dimensional (3-D) ultrasound plays an important role in obstetrics predominantly for assessing fetal anatomy. Presenting volume data in a standard anatomic orientation assists both ultrasonographers and pregnant patients to recognize anatomy more readily. Three-dimensional ultrasound is advantageous for the study of normal embryonic and/or fetal development, as well as providing information for families at risk for specific congenital anomalies by confirming normality. This method offers advantages in assessing the embryo in the first trimester as it is able to obtain multiplanar images through endovaginal volume acquisition. Rotation of the embryo and close scrutiny of the volume allow the systematic review of anatomic structures such as cord insertion, limb buds, cerebral cavities, stomach and bladder. Using this modality one can easily obtain the volumes of the gestational sac and yolk sac and can evaluate their relationship to prediction of pregnancy outcome. Three-dimensional power Doppler sonography has the potential to study process of placentation and evaluate the development of the embryonic and fetal cardiovascular systems. Three-dimensional ultrasound imaging in vivo compliments pathologic and histologic evaluation of the developing embryo, giving rise to a new term: 3-D sonoembryology. Rapid technological development will allow real-time 3-D ultrasound to provide improved and expanded patient care on the one side, and increased knowledge of developmental anatomy on the another.

Female↗