Human growth and development.
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Bronchial Arteries↗
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Preimplantation development, fate of the zona pellucida, and observations on the glycogen-rich oviduct of the little bulldog bat, Noctilio albiventris.
The reproductive biology of Noctilio albiventris was investigated histologically in 112 females collected at the start of their synchronized breeding season during two different sampling years in the Cauca Valley of Colombia. Both ovaries were functional, but the animals were generally observed to be monovular. Embryonic development in the oviduct was found to proceed to blastocyst formation and loss of the zona pellucida. In 22 animals the discarded zona had been left behind in the oviduct upon passage of the embryo into the uterus and was still undissolved at the time of amniogenesis, the latest stage examined. The zonae which had passed into the uterus with the embryos often exhibited signs of dissolution. Most of the early blastocyts were morphologically distinctive, lacking a typical inner cell mass and being instead largely bilaminar. Degenerating ova from previous ovulations were found in the oviducts of two pregnant bats, suggesting that Noctilio may be another species in which the embryo stimulates its own escape from the oviduct. During tubal passage of the embryo the secretory cells of the oviductal ampulla and isthmus exhibited a transient engorgement with glycogen, particularly on the side ipsilateral to the new corpus luteum.
Animals↗
Abnormal development of embryonic and extraembryonic cell lineages in parthenogenetic mouse embryos.
Parthenogetically activated, diploid mouse oocytes can develop to midgestation stages in utero. However, even these advanced parthenogenones appear to die because of much reduced trophoblast and yolk sac development. Previous studies have compared the general features of parthenogenetic and androgenetic development and determined the fate of uniparental cells in chimeras with normal embryos. These studies led to the concept of genomic imprinting as the cause for developmental failure when either the maternal or the paternal genome is duplicated, with the corresponding deficiency of the other. Genomic imprinting appears to arise during gametogenesis and to act through dosage effects in a set of imprinted genes, whose expression depends on their parental origin. In this study we undertook a more detailed morphological analysis of parthenogenetic development in the mouse and established a classification system to quantify the developmental extent of parthenogenones. We found that the failure of parthenogenones occurred at different times during early postimplantation development, generating a spectrum of concepti which had developed to different extents, with only a small fraction of the embryos reaching advanced somite stages. In all parthenogenones differentiation and proliferation of the trophectoderm and primitive endoderm lineages (both extraembryonic) was abnormal, and in all, even the best-developed parthenogenones, we observed similar deficiencies in the embryonic lineages, especially the mesoderm. Common to all abnormally developed lineages was that the proportion of undifferentiated precursor cells was much reduced, while their differentiated descendants were relatively abundant. We propose, therefore, that the failure of parthenogenones to develop to term is due to abnormal regulation of differentiation and proliferation in both embryonic and extraembryonic lineages. In this hypothesis, the apparent tissue specific defects observed in parthenogenones arise as a consequence of the functional importance of certain tissues (like the trophoblast) early in development. The spectrum of parthenogenones thus appears to reflect critical events in early development, whose regulation are affected by genomic imprinting.
Animals↗
Expression of epidermal growth factor family gene members in early mouse development.
Transcription of four members of the epidermal growth factor (EGF) family, EGF, TGF-alpha, Amphiregulin, and Cripto, was investigated in the ovulated unfertilized egg and preimplantation embryo using cDNA libraries. EGF was present as a maternal message only, TGF-alpha was present at low levels in each library, Amphiregulin was not detected, and Cripto transcripts were first detected in the blastocyst cDNA library. In situ hybridization studies of the implanting embryo revealed Cripto expression localized to the entire ectoderm and then to the rapidly growing ectoplacental cone. At gastrulation, Cripto was detected in the primitive streak and developing mesoderm. During organogenesis, Cripto localized to the developing heart. Two Cripto transcripts were detected: one is confined to the early embryo and teratocarcinoma cells, and the other, first found in the fetus, is the major form detected in adult organs.
Amphiregulin↗
Expression of M-twist during postimplantation development of the mouse.
The murine homologue of the Drosophila twist gene has been shown to be essential for head mesenchyme formation and to act as an inhibitor of muscle differentiation. This paper presents a detailed analysis of M-twist expression patterns from day 7 post coitum (p.c.) to day 18 p.c., indicating a more general function of the M-twist gene. At day 7 p.c., M-twist is expressed in the mesoderm outside the primitive streak. Later M-twist message is predominantly found in the somites, the head mesenchyme, the branchial arches, the limbs, and in the mesenchyme underneath the epidermis. Beginning at day 8 p.c., M-twist is mainly expressed in undifferentiated cells committed to muscle and cartilage development: this expression is consistent with a suggested role of M-twist in inhibiting overt muscle and cartilage differentiation. However, during organogenesis, M-twist is expressed in several areas of mesenchyme-epithelia interactions, suggesting additional tissue specific functions.
Animals↗
Distribution of p21ras in postimplantation rat embryos.
Expression of ras cellular oncogenes during the early postimplantation period in the rat was investigated using immunohistochemistry to p21ras. A broad spectrum polyclonal antibody recognizing N-, Ha- and Ki- forms of p21ras was used in an indirect avidin-biotin-peroxidase (ABC) technique. Positive staining indicating the presence of p21ras was found in embryos from 6.5 to 12 days embryonic age. In early egg cylinders (6.5 days), positive staining for p21ras was observed on the ectoplacental cone, primitive ectoderm and trophectoderm, while primitive endoderm and parietal endoderm appeared paler. In later egg cylinder stages (7.5 days), strong positive staining was observed in the primitive embryonic ectoderm and ectoplacental cone, but parietal and visceral endoderm still appeared to be devoid of positive staining. As development proceeded during primitive streak stages, the visceral and parietal endoderm became positively stained. By 10 days, all tissues appeared to be positive for p21ras, with strong staining appearing in the heart and neural elements. Therefore, p21ras does not appear to be ubiquitous in the rat conceptus prior to gastrulation, but shows differential distribution, appearing later in endodermal derivatives. Possibly p21ras is involved in determination of the ectodermal and endodermal lineages.
Animals↗
Zinc influences the in vitro development of peri-implantation mouse embryos.
BACKGROUND: For humans, it is estimated that over 70% of concepti are lost during early development. In culture, mouse peri-implantation embryos can mimic development from the blastocyst to the egg cylinder stage of development, a period during which implantation occurs in vivo. We describe a novel application of this model to investigate nutritional factors that may influence this stage of development. We investigated the influence of zinc (Zn) deficiency on embryonic development at the time of embryo implantation. METHODS: Mouse blastocysts were cultured for 144 hr in low Zn, Zn-replete or control medium. RESULTS: Embryos developed normally when they were cultured in the control and Zn-replete media. Embryos cultured in the low Zn medium were significantly impaired in forming egg cylinder morphology. This was associated with a reduction in extraembryonic endoderm as determined by immunohistochemistry for markers of visceral and parietal endoderm and correlated with an increase in TUNEL positive cells in the low Zn group. There was no change in the frequency of cells positive for phosphorylated Histone H3, a marker for S-phase, indicating that an increase in apoptosis was primarily responsible for the smaller size and reduction in extraembryonic endoderm. The increased cell death was not associated with an increase in reactive oxygen species (ROS) detected by dichlorodihydrofluorescein staining. CONCLUSIONS: These data support an important role for Zn in promoting differentiation and cell survival in the early embryo and suggest that sub-optimal nutrition is an important factor that contributes to defects in primary germ layers and early embryonic loss.
Animals↗
Matrix metalloproteinases and cellular motility in development and disease.
The movement of cells and the accompanied remodeling of the extracellular matrix is a critical step in many developmental processes. The matrix metalloproteinases (MMPs) are well recognized as mediators of matrix degradation, and their activity as regulators of signaling pathways by virtue of the cleavage of nonmatrix substrates has been increasingly appreciated. In this review, we focus on the role of MMPs in altering processes that influence cellular motility. MMP involvement in cellular adhesion, lamellipodia-directed movement, invadopodial protrusion, axonal growth cone extension, and chemotaxis are discussed. Although not designed to be comprehensive, these examples clearly demonstrate that cellular regulation of the MMPs influences cell motility in a variety of ways, including regulating cell-cell interactions, cell-matrix interactions, matrix degradation, and the release of bioactive signaling molecules. Deregulation of these interactions can ultimately result in disorders including inflammatory diseases, vascular diseases, bone diseases, neurological disorders, and cancer.
Animals↗
Matrix metalloproteinases in development and disease.
Matrix metalloproteinases (MMPs) are key modulators of many biological processes during pathophysiological events, such as skeletal formation, angiogenesis, cellular migration, inflammation, wound healing, coagulation, lung and cardiovascular diseases, arthritis, and cancer. Twenty-four members of the MMP family have been identified in humans, degrading many components of the extracellular matrix, cellular receptors, and cytokines. This review describes the molecular structure, activation and inhibition, and substrate specificity of MMPs, and their biological function in development and disease.
Animals↗
Visualization of molecular and cellular events with green fluorescent proteins in developing embryos: a review.
During the past 5 years, green fluorescent protein (GFP) has become one of the most widely used in vivo protein markers for studying a number of different molecular processes during development, such as promoter activation, gene expression, protein trafficking and cell lineage determination. GFP fluorescence allows observation of dynamic developmental processes in real time, in both transiently and stably transformed cells, as well as in live embryos. In this review, we include the most up-to-date use of GFP during embryonic development and point out the unique contribution of GFP visualization, which resulted in novel discoveries.
Animals↗
Temporal and spatial expression of TACC1 in the mouse and human.
TACC1 is the founding member of the evolutionarily conserved transforming acidic coiled coil genes. These genes play a role in normal development and tumorigenesis through interactions with multiple complexes involved in transcription, translation, and centrosomal dynamics. Despite its importance, detailed examination of the expression of TACC1 and splice variants has not previously been performed. In this study, the spatiotemporal distribution of the Tacc1 protein was examined immunohistochemically in cross-sections of mouse embryonic tissues. We also report the distribution of currently known/predicted TACC1 splice variants in adult humans. These results indicate that Tacc1 is regulated in a dynamic manner during embryogenesis. In adult humans, ubiquitous expression of at least one TACC1 splice variant is noted, although specific combinations of variants are evident in individual differentiated tissues. An important observation is that in the in vivo three-dimensional tissue architecture of the growing organism, both the human and mouse TACC1 protein can be localized to different subcellular compartments in a cell- and tissue-specific manner. This indicates that exploration of TACC1 function must take into account the temporal expression of specific splice variants that may perform different cell-type and tissue-specific functions. Furthermore, this analysis will provide the groundwork from which future Tacc1 knockout strategies can be designed and properly interpreted.
Alternative Splicing↗
Protein synthesis in murine organs during postimplantation development detected by two-dimensional gel electrophoresis.
Mouse embryos were isolated from the uterus on days 10 to 11 of gestation and incubated in Dulbecco's modified Eagle's medium (DMEM) with [35S]methionine for 4 h. Subsequently, their hearts and the brains were dissected. The brain was divided into three parts, containing the telencephalon, mesencephalon, and myelencephalon. These tissues were then processed for two-dimensional (2-D) gel electrophoresis. Protein synthesis of the isolated tissues was analyzed for organ-and cell lineage-specific patterns. We studied proteins with isoelectric points (pI) ranging from 4 to 10 and relative molecular weights (M(r)) varying from 10000 to 200000 and found several significant quantitative and qualitative differences between the tissues and the developmental stages analyzed. In particular, we were able to distinguish between protein spots that we now attribute putatively to the corresponding embryonic organs. These differences may reflect some of the organ- and cell lineage-specific changes in protein synthesis and gene expression during early mammalian differentiation.
Animals↗
Expression pattern of the Brachyury gene in the arrow worm paraspadella gotoi (chaetognatha).
Arrow worms (the phylum Chaetognatha), which are among the major marine planktonic animals, are direct developers and exhibit features characteristic of both deuterostomes and protostomes. In particular, the embryonic development of arrow worms appears to be of the deuterostome type. Brachyury functions critically in the formation of the notochord in chordates, whereas the gene is expressed in both the blastopore and stomodeum invagination regions in embryos of hemichordates and echinoderms. Here we analyzed the expression of Brachyury (Pg-Bra) in the arrow worm Paraspadella gotoi and showed that Pg-Bra is expressed in the blastopore region and the stomodeum region in the embryo and then around the mouth opening region at the time of hatching. The expression of Pg-Bra in the embryo resembles that of Brachyury in embryos of hemichordates and echinoderms, whereas that in the mouth opening region in the hatchling appears to be novel.
Amino Acid Sequence↗
Dynamic in vivo imaging of postimplantation mammalian embryos using whole embryo culture.
Due to the internal nature of mammalian development, much of the research performed is of a static nature and depends on interpolation between stages of development. This approach cannot explore the dynamic interactions that are essential for normal development. While roller culture overcomes the problem of inaccessibility of the embryo, the constant motion of the medium and embryos makes it impossible to observe and record development. We have developed a static mammalian culture system for imaging development of the mouse embryo. Using this technique, it is possible to sustain normal development for periods of 18-24 h. The success of the culture was evaluated based on the rate of embryo turning, heart rate, somite addition, and several gross morphological features. When this technique is combined with fluorescent markers, it is possible to follow the development of specific tissues or the movement of cells. To highlight some of the strengths of this approach, we present time-lapse movies of embryonic turning, somite addition, closure of the neural tube, and fluorescent imaging of blood circulation in the yolk sac and embryo.
Air↗
Mutation of the SNF2 family member Chd2 affects mouse development and survival.
The chromodomain helicase DNA-binding domain (Chd) proteins belong to the SNF2-like family of ATPases that function in chromatin remodeling and assembly. These proteins are characterized by the presence of tandem chromodomains and are further subdivided based on the presence or absence of additional structural motifs. The Chd1-Chd2 subfamily is distinguished by the presence of a DNA-binding domain that recognizes AT-rich sequence. Currently, there are no reports addressing the function of the Chd2 family member. Embryonic stem cells containing a retroviral gene-trap inserted at the Chd2 locus were utilized to generate mice expressing a Chd2 protein lacking the DNA-binding domain. This mutation in Chd2 resulted in a general growth delay in homozygous mutants late in embryogenesis and in perinatal lethality. Animals heterozygous for the mutation showed decreased neonatal viability and increased susceptibility to non-neoplastic lesions affecting most primary organs. In particular, approximately 85% of the heterozygotes showed gross kidney abnormalities. Our results demonstrate that mutation of Chd2 dramatically affects mammalian development and long-term survival.
Animals↗
Glycine protects preimplantation mouse conceptuses from a detrimental effect on development of the inorganic ions in oviductal fluid.
Two-cell mouse conceptuses were cultured in media that contained various concentrations of inorganic ions and amino acids. Substrates of the amino acid transport system Gly were detrimental to development at slightly hyposmotic concentrations of other ions. In contrast, these amino acids increased the frequency at which two-cell conceptuses developed into blastocysts at total ion concentrations of 355 to 405 mM. Data reported elsewhere is consistent with the possibility that the total ion concentration in oviductal fluid exceeds 360 mM, whereas the concentration of glycine in this fluid may be on the order of 10 mM. Therefore, a high ion concentration and glycine may counteract the potentially harmful effects of each other in situ. Like some marine organisms, preimplantation mouse conceptuses may use glycine as an intracellular osmolite because accumulation of inorganic ions could perturb the activities of some enzymes.
Amino Acids↗
Embryological origins of developmental stability: size, shape and fluctuating asymmetry in prenatal random bred mice.
Ontogenetic patterns of fluctuating asymmetry (FA) can be used to test models for the mechanisms underlying stability during embryonic development (developmental stability). In this study, we ask whether developmental processes initially show high levels of instability that are subsequently dampened through active compensatory mechanisms or passive properties of developmental systems or whether the effects of instability accumulate during embryonic development causing random drift away from an earlier stable state. Previous work on this question has dealt with postnatal skeletal growth and thus been unable to effectively distinguish developmental instability from the effects of mechanically mediated variation in bone modeling and remodeling. Here, we report that FA variances of limb skeletal elements in CD1 mice decrease with gestational age from day 14 to birth (day 20.5). Thus, in mouse limbs, skeletal development is characterized by a high level of developmental instability initially that is reduced during subsequent prenatal development. These results are consistent with the existence of active mechanisms that compensate for the effects of minor perturbations or deviations during development. However, they are also consistent with Soule's model of allomeric variation in which the variance of structures is reduced as the number of independent developmental events that produce them increases. This study illustrates that predictions based on morphometric analyses can yield insights into general properties of developmental systems in cases where specific developmental mechanisms are not yet known.
Animals↗
Epidermal differentiation during ontogeny and after hatching in the snake Liasis fuscus (Pythonidae, Serpentes, Reptilia), with emphasis on the formation of the shedding complex.
Differentiation and localization of keratin in the epidermis during embryonic development and up to 3 months posthatching in the Australian water python, Liasis fuscus, was studied by ultrastructural and immunocytochemical methods. Scales arise from dome-like folds in the skin that produce tightly imbricating scales. The dermis of these scales is completely differentiated before any epidermal differentiation begins, with a loose dermis made of mesenchymal cells beneath the differentiating outer scale surface. At this stage (33) the embryo is still unpigmented and two layers of suprabasal cells contain abundant glycogen. At Stage 34 (beginning of pigmentation) the first layers of cells beneath the bilayered periderm (presumptive clear and oberhautchen layers) have not yet formed a shedding complex, within which prehatching shedding takes place. At Stage 35 the shedding complex, consisting of the clear and oberhautchen layers, is discernible. The clear layer contains a fine fibrous network that faces the underlying oberhautchen, where the spinulae initially contain a core of fibrous material and small beta-keratin packets. Differentiation continues at Stage 36 when the beta-layer forms and beta-keratin packets are deposited both on the fibrous core of the oberhautchen and within beta-cells. Mesos cells are produced from the germinal layer but remain undifferentiated. At Stage 37, before hatching, the beta-layer is compact, the mesos layer contains mesos granules, and cells of the alpha-layer are present but are not yet keratinized. They are still only partially differentiated a few hours after hatching, when a new shedding complex is forming underneath. Using antibodies against chick scale beta-keratin resolved at high magnification with immunofluorescent or immunogold conjugates, we offer the first molecular confirmation that in snakes only the oberhautchen component of the shedding complex and the underlying beta cells contain beta-keratin. Initially, there is little immunoreactivity in the small beta-packets of the oberhautchen, but it increases after fusion with the underlying cells to produce the syncytial beta layer. The beta-keratin packets coalesce with the tonofilaments, including those attached to desmosomes, which rapidly disappear in both oberhautchen and beta-cells as differentiation progresses. The labeling is low to absent in forming mesos-cells beneath the beta-layer. This study further supports the hypothesis that the shedding complex in lepidosaurian reptiles evolved after there was a segregation between alpha-keratogenic cells from beta-keratogenic cells during epidermal renewal.
Animals↗