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PubMed2001

Function of vitamin A in vertebrate embryonic development.

Advances in molecular biology and retinoic acid receptor research have significantly contributed to the understanding of the role of vitamin A during vertebrate development. Examination of the function of this vitamin during very early developmental stages using the completely vitamin A-depleted avian embryo has revealed that the vitamin A requirement begins at the time of formation of the primitive heart, circulation and specification of hindbrain. The lack of vitamin A at this critical time results in gross abnormalities and early embryonic death. In rodent models, vitamin A deficiency can be targeted to later gestational windows and documents the need for vitamin A for more advanced stages of development. Major target tissues of vitamin A deficiency include the heart, central nervous system and structures derived from it, the circulatory, urogenital and respiratory systems, and the development of skull, skeleton and limbs. These abnormalities are also evident in mice mutants from retinoid receptor knockouts; they have revealed both morphological and molecular aspects of vitamin A function during development. Retinoic acid receptors (RAR) in partnership with retinoid X receptor (RXR)alpha appear to be the important retinoid receptor transcription factors regulating vitamin A function at the gene level during development via the physiologic ligand all-trans-retinoic acid. Homeostasis of retinoic acid is maintained by developmentally regulated vitamin A metabolism enzyme systems. Inadequate vitamin A nutrition during early pregnancy may account for some pediatric congenital abnormalities.

Animals↗

PubMed1996

High level expression of the HMGI (Y) gene during embryonic development.

The HMGI protein family includes three proteins, named HMG-I, HMG-Y and HMGI-C. The first two proteins are coded for by the same gene, HMGI (Y), through an alternative splicing mechanism. Their expression is elevated in neoplastic tissues and cells and this overexpression has a causal role in the process of cellular neoplastic transformation. We demonstrate that the HMGI (Y) gene is expressed at very low levels in normal adult tissues, whereas in embryonic tissues it is expressed at high levels comparable to those detected in neoplastic tissues. Specifically, a very high expression of the HMGI (Y) gene was detected in all embryonic tissues at 8.5 dpc. Then in the following days, even though the gene is expressed essentially in all tissues, an abundant gene expression was restricted to some tissues. These results indicate an important role of the HMGI (Y) gene in development.

Adult↗

PubMed1995

Restricted expression of type-II TGF beta receptor in murine embryonic development suggests a central role in tissue modeling and CNS patterning.

The type-II TGF beta receptor mediates many of the biological responses to TGF beta. An examination of the expression of the type-II TGF beta receptor during mouse embryogenesis therefore provides specific information about the role of TGF beta during embryogenesis than has been available to date. We have isolated the genomic murine homologue of the human type-II TGF beta receptor corresponding to exon 2. The murine and human sequences show a high degree of homology. Using the murine probe, we found that type-II TGF beta receptor expression is regulated in both a spatial and a temporal fashion by using in situ hybridization and ribonuclease protection assays. Type-II TGF beta receptor expression is localized to the mesenchyme during critical interactions with adjacent epithelium such as developing hair follicles, whisker follicles and tooth anlage. In the central nervous system, type-II TGF beta receptor expression is highly restricted to the floor plate. Strong expression is also detected in migrating neural crest cells, meninges, and choroid plexus. Specific mesenchymal localization of type-II TGF beta receptor is also observed in lung, kidney, intestine, stomach, and bladder. The restricted expression of type-II TGF beta receptor in mesenchymal cells at sites of epithelial-mesenchymal interactions suggests that type-II TGF beta receptor plays a major role in mediating the establishment of embryonic organ systems. The highly restricted expression of type-II TGF beta receptor in the developing CNS suggests an important role for a serine/threonine kinase in patterning of the nervous system.

Aging↗

PubMed1995

Effects of a gonadotropin releasing hormone agonist on oocyte maturation, fertilization, and embryonal development of mice.

PURPOSE: The effects of a GnRH agonist (GnRHa) on oocyte quality were investigated by assessing the influence of GnRHa on oocytes, and fertilized oocytes were examined in vivo and in vitro. Administration of gonadotropin in conjunction with GnRHa induced a significantly greater degree of germinal vesicle breakdown, significantly higher rates of in vitro fertilization, and significantly faster development of the oocytes than the pregnant mare serum gonadotropin alone RESULTS: The hatching-success rate in the GnRHa treated hypophysectomized mice was higher than in control mice. The rate of in vitro fertilization was also higher in oocytes cultured in the presence of low loses of GnRHa and these effects were reversed by a GnRH antagonist. CONCLUSION: Oocytes obtained following ovarian stimulation with GnRHa were of higher quality than control oocytes, and the efficacy of GnRHa may be due in part to its direct action on the ovary.

Animals↗

PubMed1988

Evaluation of Chang's culture medium for mouse in vitro fertilization and embryonic development.

Chang's medium [with and without human serum (HS)] was compared with T6 medium [with and without bovine serum albumin (BSA)] for in vitro fertilization (IVF) and development of two-cell mouse embryos to the blastocyst stage. Chang's medium without any supplementation gave significantly better fertilization rates (83.3%) than Chang's with 10% HS (76.4%) or T6 and BSA (76.6%) (P less than 0.01). In a separate experiment 87.7% of the two-cell mouse embryos developed to the blastocyst stage in Chang's medium, compared to 90.6% for T6 with BSA and 93.6% without BSA, respectively (P greater than 0.01). In Chang's medium supplemented with 10% HS, 76.6% of the embryos developed to the blastocyst stage and 17.2% stopped development after the morula stage. After 72 hr in vitro hatched trophoblast and inner-cell-mass cells from 26.5 and 30.8% of the embryos grown in Chang's medium (with and without HS) attached to the plastic culture dishes and grew to form a mixed monolayer of epithelioid and fibroblastic cells. Chang's medium can thus be successfully used for IVF and growth of mammalian embryos. Further, inner cell mass and trophoblast cell lines could be established for various reproductive studies using this medium.

Animals↗

PubMed1992

Fertilization and early embryonic development.

Whether one carefully and meticulously records detailed observations in the laboratory, or jumps feet first into new and exciting areas of investigation, each scientist contributes to the advances being made in the control of human reproduction. The study of spermatozoa, oocytes, sperm-oocyte interaction, preembryo growth and development, and early pregnancy rewards us with breakthroughs in innovative technology and promotes paths of better understanding. One cannot search through the massive amounts of currently available literature without desiring to try "this" technique, expound on "that" one, take someone else's work a little further, or look at one's own results from a different angle. Presented here are some informative data, most published within the past year. Oocyte maturational competence and integrity, sperm function and quality, preembryo culture conditions, preembryo morphology, and ovarian age all emerge as factors important for interpreting a patient's chance of achieving pregnancy.

Embryonic and Fetal Development↗

PubMed1999

Special relationship of gamma-aminobutyric acid to the ventromedial nucleus of the hypothalamus during embryonic development.

The ventromedial nucleus of the hypothalamus (VMH) is a key nucleus for regulating homeostatic, neuroendocrine, and behavioral functions. We conducted immunocytochemical analyses by using antisera directed against gamma-aminobutyric acid (GABA), its synthetic enzyme glutamic acid decarboxylase (GAD67), GABA-A receptor subunits (alpha2, beta3, epsilon), estrogen receptor-alpha, and Neuropeptide Y (NPY) in the region of the VMH in embryonic mice to identify potential patterning elements for VMH formation. Cells and fibers containing GABA and GAD67 encircled the primordial VMH as early as embryonic day 13 (E13) when the cytoarchitecture of the VMH was not recognizable by Nissl stain. At E16-17 the cytoarchitecture of the VMH became recognizable by Nissl stain as GABAergic fibers invaded the nucleus, continued postnatally, and by adulthood the density of GABAergic fibers was greater inside than outside the VMH. GABA-A receptor subunit expression (beta3 by E13 and alpha2 by E15) within the primordial VMH suggested potential sensitivity to the surrounding GABA signal. Brain slices were used to test whether fibers from distal or proximal sites influenced VMH development. Coronal Vibratome slices were prepared and maintained in vitro for 0-3 days. Nissl stain analyses showed a uniform distribution of cells in the region of the VMH on the day of plating (E15). After 3 days in vitro, cellular aggregation suggesting VMH formation was seen. Nuclear formation in vitro suggests that key factors resided locally within the coronal plane of the slices. It is suggested that either GABA intrinsic to the region nearby the VMH directly influences the development and organization of the VMH, or along with other markers provides an early indicator of pattern determination that precedes the cellular organization of the VMH.

Animals↗

PubMed1994

[Studies on embryonal development of lamina cribrosa of human eyes].

The lamina cribrosa of 291 eyes were studied including 260 eyes taken from embryos and fetus of 7 weeks to full term and 31 eyes from infants under 1 year of age. From the observations, it is discovered that the development of the lamina cribrosa lags behind the development of the optic nerve. In the eyes taken from embryos or fetus < 4 months, only the ectodermal primordium of the lamina cribrosa is seen. The initial scleral part of the lamina cribrosa begins to be formed in the 5th month fetus. The fibrous tissue originating from the choroid and optic nerve sheath contributes the formation of the lamina cribrosa in the 8th month fetus. At this time, the morphology of the lamina cribrosa is similar to that of an adult, but the thickness of the structure is still increasing till one year after birth.

Child, Preschool↗

PubMed1990

[Embryonal development and the structure of the intermesenteric plexus in humans and various mammals].

The intermesenteric plexus is an independent formation, it is connected with other plexuses in the abdominal and pelvic cavities and participates in innervation of organs. In the species investigated (mole, rat, cat, dog, man) connections between the intermesenteric and other vegetative plexuses in the abdominal and pelvic cavities vary according to their amount and complexity, they are most abundant and complex in man. In the latter the plexus is also mostly rich in neuro-fibrillar and neuro-cellular elements. In the intermesenteric plexus of the man and the animals studied there is a rather big part of vegetative ganglia, which can be considered as peripheral centers of the internal abdominal organs innervation.

Animals↗

PubMed1998

Chromatin remodelling and nuclear reprogramming at the onset of embryonic development in mammals.

Two main strategies are used to produce cloned mammals. The first involves the condensation of donor chromatin into chromosomes directly exposed to the recipient cytoplasm, whereas the second leaves the donor nucleus in interphase until the time of the first mitosis. Both strategies, which induce marked changes in chromatin organization, allow full reprogrammation of somatic-differentiated fetal and adult cells. This paper reviews some of the recent data that contribute to our understanding of chromatin remodelling at the onset of normal development, as well as after the introduction of a foreign nucleus into a recipient enucleated oocyte. These data indicate that the coordinated changes in chromatin organization that take place up until the first cellular differentiations at the blastocyst stage are determinants for successful cloning. Although some degree of synchronization between the cell cycle stages of donor and recipient cells is necessary for correct remodelling of a transferred nucleus, the kinetics of remodelling events occurring during the one-cell stage appears to be the determining factor for the normal onset of gene expression.

Adult↗

PubMed1996

Chromatin and gene regulation at the onset of embryonic development.

Major transitions in chromosome and chromatin structure occur during development. Recent genetic and biochemical experiments demonstrate that these alterations in genome organization make significant contributions to establishing and maintaining states of differential transcriptional activity. Developmentally regulated changes in histone variants have a causal role in determining patterns of gene activity, directing the repression of specific eukaryotic genes. Chromosomal proteins such as Polycomb stabilize and maintain transcriptionally repressed states. Proteins regulating mitotic chromosome condensation have a role in determining the overall transcriptional activity of a chromosome. In this review, I place the developmental roles of these chromosomal constituents in a structural and functional context. Considerable insight now exists into the molecular mechanisms regulating chromosomal activity during development. Chromosomal architecture is emerging as a key controlling influence in the developmental regulation of gene expression. Recent genetic experiments using Caenorhabditis elegans, Drosophila melanogaster and the mouse have provided clear evidence for the functional differentiation of chromosomal structures during development. Chromosomes are visualized as highly specialized entities, within which the activity of particular domains is largely determined by defined structural proteins. At a more local level, the mechanisms regulating gene transcription during early embryogenesis in Xenopus and the mouse have been found to be dependent on the biochemical composition of individual nucleosomes. Thus, variation in the type and modification of chromosomal and chromatin structural proteins provides a dominant means of controlling the transcriptional activity of individual genes, individual chromosomal domains and of entire chromosomes. The focus of this review is to summarize these recent advances and to discuss their implications for developmental biology.

Animals↗

PubMed1997

Transcription factor Sp1 is essential for early embryonic development but dispensable for cell growth and differentiation.

Transcription factor Sp1 has been implicated in the expression of many genes. Moreover, it has been suggested that Sp1 is linked to the maintenance of methylation-free CpG islands, the cell cycle, and the formation of active chromatin structures. We have inactivated the mouse Sp1 gene. Sp1-/- embryos are retarded in development, show a broad range of abnormalities, and die around day 11 of gestation. In Sp1-/- embryos, the expression of many putative target genes, including cell cycle-regulated genes, is not affected, CpG islands remain methylation free, and active chromatin is formed at the globin loci. However, the expression of the methyl-CpG-binding protein MeCP2 is greatly reduced in Sp1-/- embryos. MeCP2 is thought to be required for the maintenance of differentiated cells. We suggest that Sp1 is an important regulator of this process.

Animals↗

PubMed1994

The Drosophila maternal effect locus deadhead encodes a thioredoxin homolog required for female meiosis and early embryonic development.

This study describes the identification, function and molecular characterization of deadhead, a Drosophila thioredoxin homolog. Although in vitro studies have shown that thioredoxin can post-translationally regulate the activity of many different proteins, we find that this homolog is not essential for viability. The phenotypic analysis of two different mutations which eliminate function suggests that dhd is essential for female meiosis. The majority of eggs laid by females homozygous for null mutations are fertilized but fail to complete meiosis. A small number of escaper embryos initiate development and display a range of phenotypes suggesting functions in both preblastoderm mitosis and head development. Our analysis of deadhead's RNA expression pattern is consistent with its maternal effect function: the RNA is predominately expressed in the nurse cells of the ovary, is maternally deposited into the egg, but does not appear to be zygotically expressed during embryogenesis. Thus both our genetic and molecular data are consistent with a function during meiosis and preblastoderm mitosis. Whether the head defect indicates an additional function or is an indirect consequence of earlier defects remains to be determined.

Amino Acid Sequence↗

PubMed1999

Three-dimensional reconstruction of the ventral and dorsal pancreas: a new insight into anatomy and embryonic development.

The recent introduction of limited resections of the ventral pancreas for benign disease and for low-grade malignancies calls for a thorough understanding of its anatomy. The two embryonic anlagen were characterized and distinguished through a comprehensive study of their macroscopic, histologic, and immunohistochemical characteristics in 20 autopsy specimens before reconstruction. Sections were histologically stained with hematoxylin-eosin and Grimelius and immunohistochemically stained with antibodies to insulin, glucagon, somatostatin, and pancreatic polypeptide by the avidin biotin complex method. The ventral and dorsal anlagen of the pancreas were reconstructed from eight autopsy specimens, using the "macroserial" method, after serial sectioning and immunohistochemical staining with anti-pancreatic polypeptide antibodies. Compared with the dorsal pancreas, the ventral pancreas was characterized by the presence of smaller and more closely packed lobuli, irregular rather than uniform islets of Langerhans, and rich immunostaining with anti-pancreatic polypeptide. Construction of the two anlagen showed that the dorsal pancreas consisted of the anterior part of the head of the pancreas, and the body and tail of the pancreas, while the ventral pancreas consisted of the posterior part of the head of the gland and the upper two-thirds (62.5%) or all (37.5%) of the uncinate process. The ventral pancreas was related to the right lateral surface of the superior mesenteric vein extending to the back. However, it did not extend across the front surface of the superior mesenteric vein to the left as previously described. The uncinate process was also located posterior to but not anterior to the superior mesenteric vein. The contributions of the ventral and dorsal anlagen to the anatomy of the pancreas gland as demonstrated in this study differ, in some relevant features, from the classical descriptions in the medical literature. The current anatomical findings add essential knowledge for the pancreatic surgeon who contemplates tissue-preserving resections.

Adolescent↗

PubMed2004

Systematic analysis of hematopoietic, vasculogenetic, and angiogenetic phases in the developing embryonic avian lung, Gallus gallus variant domesticus.

In the embryonic lung of the domestic fowl, Gallus gallus variant domesticus, hematogenetic and vasculogenetic cells become ultrastructurally clear from day 4 of development. In the former group of cells, filopodial extensions coalesce, cytoplasm thickens, and accumulating hemoglobin displaces the nucleus peripherally while in the latter, conspicuous filopodial extensions and large nuclei develop as the cells assume a rather stellate appearance. From day 5, erythrocytes and granular leukocytes begin forming from cytoarchitecturally cognate hematogenetic cells. The cells become distinguishable when hemoglobin starts to accumulate in the erythroblasts and electron dense bodies form in the leukoblasts. Vasculogenesis begins from day 7 in different areas of the developing lung: erthrocytes (but not granular leukocytes) appear to attract committed vasculogenetic cells (angioblasts) that form an endothelial lining and vessel wall. Arrangement of angioblasts around forming blood vessels sets the direction along which the vessels sprout (angiogenesis). In some areas of the developing lung, through what seems like an inductive erythropoietic process, arcades of erythrocytes organize. Once endothelial cells surround such continuities, discrete vascular units organize. By day 10, the major parts of the in-built (intrinsic) pulmonary vasculature are assembled. Complete pulmonary circulation (i.e., through the exchange tissue) is not established until after day 18 when the blood capillaries start to develop. Since the precursory erythrocytes do not have a respiratory role, it is imperative that de novo erythropoiesis is essential for vasculogenesis. Diffuse (fragmentary) development and subsequent piecemeal assembly of the pulmonary vascular system may explicate the fabrication of a complex circulatory architecture that grants cross-current, counter-current, and multicapillary serial arterialization designs in the exchange tissue of the avian lung. The exceptional respiratory efficiency of the avian lung is largely attributable to the geometries (physical interfacing) between the bronchial and vascular elements at different levels of morphological organization.

Animals↗

PubMed1985

Mouse teratocarcinoma and embryonic development. Two-dimensional protein patterns in nerve differentiation.

The transition in mouse teratocarcinomas of pluripotential stem cells to histogenetically determined ones of the neurogenic cell lineage was analysed at the total cellular protein level by two-dimensional gel electrophoresis. The change in morphology and function was found to be reflected by extensive shifts in the protein synthesis patterns. From a total of about 1000 resolved polypeptides that are synthesized in embryoid bodies of a multidifferentiating teratocarcinoma, about 12% (117 proteins) are not found or only present at a very much reduced level in two teratocarcinoma-derived neuroblastomas. On the other hand, the change in phenotype is accompanied by the de novo or greatly enhanced synthesis of another 69 proteins (about 7%) in the neurogenic tumors. In a screening for differentiation-specific proteins this set was compared with the protein synthesized in neural tissue of maturing brain and muscle tissue of developing limbs at three different postimplantation stages covering the onset of organogenesis. This comparison disclosed that a great portion of the differentiation-related proteins (26 proteins) are synthesized in both brain and muscle and are probably required by a differentiated cell in general like cytostructural proteins. Seventeen polypeptides, however, are synthesized in a cell type specific manner. In particular, 4 proteins that are synthesized in both neurogenic tumors and in brain but not in muscle tissue were tentatively called nerve-specific proteins (NSP) and are the most promising in further analyses of differentiation-specific proteins.

Animals↗

PubMed1998

[Effects of chemical mixtures on embryonic development: examples of experimental models and problems in risk assessment].

Toxicological risk deriving from the exposure to mixtures of toxic substances, the study of possible interactions among them and their mechanisms of action are of special interest in prenatal toxicology. In fact, embryo is a dynamic complex system whose gradual development substantially modulates the extent and type of damages to which it may be sensitive, through specific, critical periods of sensitivity. In this paper, a number of types of interactions among toxic substances which show the same mechanisms of action and/or the same target site, are analysed. Besides, pharmacokinetic interactions among teratogenic agents and substances modulating their metabolism, need specific evaluations because of the wide variability of possible events. In conclusion, risk assessment in prenatal toxicology has to put greater attention to the various types of effect and pharmacokinetic interaction since they might result in an increasing risk at low doses.

Animals↗

PubMed1995

Mouse embryonic development and tumor cell growth under the influence of recombinant trichosanthin (a ribosome inactivating protein) and its muteins.

Trichosanthin, a ribosome inactivating protein, is known to possess embryotoxic and antiproliferative activities. In the present study recombinant trichosanthin and its muteins produced by site-directed mutagenesis were tested for these activities using whole embryo culture and cell culture. The results revealed that when Glu 160 in trichosanthin was mutated to alanine or aspartate, the two aforementioned activities underwent a substantial decrease. However, the former mutein had a higher potency than the latter mutein. When both Glu 160 and Glu 189 were mutated, the resultant mutant possessed very low antiproliferative and yet considerable embryotoxic activity, indicating the contribution from other amino acids in stabilizing the transition state complex of trichosanthin.

Animals↗