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PubMed1991

Genetic and cytological control of the asymmetric divisions that pattern the Volvox embryo.

The highly regular pattern in which approximately 2000 small somatic cells and 16 large reproductive cells (or 'gonidia') are arranged in a typical asexual adult of Volvox carteri can be traced back to a stereotyped program of embryonic cleavage divisions. After five symmetrical divisions have produced 32 cells of equal size, the anterior 16 cells cleave asymmetrically, to produce one small somatic cell initial and one larger gonidial initial each. The gonidial initials then cease dividing before the somatic cell initials do. The significance of the visibly asymmetric divisions is underscored by genetic and experimental evidence that differences in size--rather than differences in cytoplasmic quality--are causally important in activating the programs that cause small cells to become mortal somatic cells and large cells to differentiate as reproductive cells. A number of loci, including at least five mul ('multiple gonidia') loci, appear to be responsible for determining where and when asymmetric divisions will occur, since mutations at these loci result in modified temporal and/or spatial patterns of asymmetric division in one or more portions of the life cycle. But the capacity to divide asymmetrically at all appears to require a function encoded by the gls (gonidialess) locus, since gls mutants fail to execute any asymmetric divisions. Second-site suppressors of gls that have been identified may encode other functions required for asymmetric division. Cytological and immunocytochemical studies of dividing embryos are being undertaken in an attempt to elucidate the mechanisms by which cell-division planes are established--and shifted--under the influence of such pattern-specifying genes. Studies to date clearly indicate a central role for the basal body apparatus, and particularly its microtubular rootlets, in establishing the orientation of both the mitotic spindle and the cleavage furrow; but it remains to be determined how behavior of the division apparatus becomes modified during asymmetric division.

Animals↗

PubMed2002

Pesticide Roundup provokes cell division dysfunction at the level of CDK1/cyclin B activation.

To assess human health risk from environmental chemicals, we have studied the effect on cell cycle regulation of the widely used glyphosate-containing pesticide Roundup. As a model system we have used sea urchin embryonic first divisions following fertilization, which are appropriate for the study of universal cell cycle regulation without interference with transcription. We show that 0.8% Roundup (containing 8 mM glyphosate) induces a delay in the kinetic of the first cell cleavage of sea urchin embryos. The delay is dependent on the concentration of Roundup. The delay in the cell cycle could be induced using increasing glyphosate concentrations (1-10 mM) in the presence of a subthreshold concentration of Roundup 0.2%, while glyphosate alone was ineffective, thus indicating synergy between glyphosate and Roundup formulation products. The effect of Roundup was not lethal and involved a delay in entry into M-phase of the cell cycle, as judged cytologically. Since CDK1/cyclin B regulates universally the M-phase of the cell cycle, we analyzed CDK1/cyclin B activation during the first division of early development. Roundup delayed the activation of CDK1/cyclin B in vivo. Roundup inhibited also the global protein synthetic rate without preventing the accumulation of cyclin B. In summary, Roundup affects cell cycle regulation by delaying activation of the CDK1/cyclin B complex, by synergic effect of glyphosate and formulation products. Considering the universality among species of the CDK1/cyclin B regulator, our results question the safety of glyphosate and Roundup on human health.

Animals↗

PubMed2002

Periods and stages of the prenatal development of the domestic cat.

Twenty-two stages of the prenatal development of the domestic cat are described for intraspecies comparison in embryological studies. These are assigned to the 15 embryonal periods based on the Nomina Embryologica Veterinaria to make the interspecies comparison possible.

Animals↗

PubMed1995

Stimulatory effects of insulin on the development of bovine embryos fertilized in vitro.

To obtain information about the effects of insulin on the development of bovine embryos, fertilized bovine embryos in vitro were cultured in a chemically defined, protein-free medium: modified synthetic oviduct fluid (mSOF) supplemented with 1 mg/ml polyvinyl alcohol (PVA). The percentage of embryos reaching the morula stage was not affected by the addition of 5 micrograms/ml insulin alone, but insulin showed a beneficial synergistic effect with amino acids (AAs) on the embryonic development to morula. Supplementation of insulin (1-100 micrograms/ml) with mSOF+AAs did not improve the percentage of embryos developing to the blastocyst stage. However, a significant increase in cell numbers of blastocysts was observed with the addition of 1 mM glucose and 1 or 10 micrograms/ml insulin from the morula stage. These results show that insulin has a beneficial effect on the preimplantation development of bovine embryos in the presence of AAs and/or glucose, and suggest that insulin improves embryonic development by stimulating AAs transport and/or glucose uptake.

Animals↗

PubMed1992

Generation and migration of cells in the developing striatum.

The development of the rat striatum was investigated using a combination of two histochemically distinguishable retrovirus vectors. Using this method, it was possible to identify clonal boundaries within the embryonic striatum and thus determine patterns of proliferation, migration, and some lineal relationships. Several novel aspects of striatal histogenesis were discovered. Striatal progenitor cells do not exhibit a stem cell pattern of division between embryonic day 15 (E15) and E19; a progenitor-progeny relationship appears to exist for ventricular zone and subventricular zone (SVZ) cells; striatal progenitors produce a variety of clone types; some SVZ cells migrate radially, and some migrate tangentially within the SVZ; and radial glia and presumptive neurons can occur in the same clone.

Alkaline Phosphatase↗

PubMed2002

Control of developmental timing by micrornas and their targets.

In Caenorhabditis elegans the timing of many developmental events is regulated by heterochronic genes. Such genes orchestrate the timing of cell divisions and fates appropriate for the developmental stage of an organism. Analyses of heterochronic mutations in the nematode C. elegans have revealed a genetic pathway that controls the timing of post-embryonic cell divisions and fates. Two of the genes in this pathway encode small regulatory RNAs. The 22 nucleotide (nt) RNAs downregulate the expression of protein-coding mRNAs of target heterochronic genes. Analogous variations in the timing of appearance of particular features have been noted among closely related species, suggesting that such explicit control of developmental timing may not be exclusive to C. elegans. In fact, some of the genes that globally pattern the temporal progression of C. elegans development, including one of the tiny RNA genes, are conserved and temporally regulated across much of animal phylogeny, suggesting that the molecular mechanisms of temporal control are ancient and universal. A very large family of tiny RNA genes called microRNAs, which are similar in structure to the heterochronic regulatory RNAs, have been detected in diverse animal species and are likely to be present in most metazoans. Functions of the newly discovered microRNAs are not yet known. Other examples of temporal programs during growth include the exquisitely choreographed temporal sequences of developmental fates in neurogenesis in Drosophila and the sequential programs of epidermal coloration in insect wing patterning. An interesting possibility is that microRNAs mediate transitions on a variety of time scales to pattern the activities of particular target protein-coding genes and in turn generate sets of cells over a period of time. Plasticity in these microRNA genes or their targets may lead to changes in relative developmental timing between related species, or heterochronic change. Instead of inventing new gene functions, even subtle changes in temporal expression of pre-existing control genes can result in speciation by altering the time at which they function.

Animals↗

PubMed1997

Miranda directs Prospero to a daughter cell during Drosophila asymmetric divisions.

Asymmetric cell division is a general process used in many developmental contexts to create two differently fated cells from a single progenitor cell. Intrinsic mechanisms like the asymmetric transmission of cell-fate determinants during cell division, and extrinsic cell-interaction mechanisms, can mediate asymmetric divisions. During embryonic development of the Drosophila central nervous system, neural stem cells called neuroblasts divide asymmetrically to produce another multipotent neuroblast and a ganglion mother cell (GMC) of more restricted developmental potential. Intrinsic mechanisms promote asymmetric division of neuroblasts: for example, the transcription factor Prospero localizes to the basal cell cortex of mitotic neuroblasts and then segregates exclusively into the GMC, which buds off from the basal side of the neuroblast. In the GMC, Prospero translocates to the nucleus, where it establishes differential gene expression between sibling cells. Here we report the identification of a gene, miranda, which encodes a new protein that co-localizes with Prospero in mitotic neuroblasts, tethers Prospero to the basal cortex of mitotic neuroblasts, directing Prospero into the GMC, and releases Prospero from the cell cortex within GMCs. miranda thus creates intrinsic differences between sibling cells by mediating the asymmetric segregation of a transcription factor into only one daughter cell during neural stem-cell division.

Alleles↗

PubMed1996

The influence of transforming growth factor beta 1 on the development of embryonic mouse long bones.

Transforming growth factor beta (TGF-beta) is an important regulator of bone metabolism, and is found in large quantities in embryonic and adult bone tissue. The influence of TGF-beta 1 on chondro-osteogenesis was studied. In organ cultures of developing long bone rudiments of embryonic mice, growth and development of the various cartilaginous and osseous compartments were investigated by morphometric analysis and autoradiography after [3H]-thymidine labelling. TGF-beta 1 (1 ng/ml) inhibited both chondrogenesis and osteogenesis, and also inhibited matrix calcification. The effect was greatest in cell populations with the highest proliferation rate. It was noticed that the bone collar formation was inhibited. This may be due to an inhibition of osteoblast proliferation or differentiation, but it seems more likely to be an inhibition of the manufacture of matrix substance. These data suggest that TGF-beta 1 may be an important regulator of embryonic bone development.

Animals↗

PubMed2000

Paternal effects from methamidophos administration in mice.

In this study, the mouse was used to evaluate paternal germline exposure to the organophosphate methamidophos for its potential to produce adverse effects on spermatozoa and in the offspring. There have been reports that organophosphate exposure can increase abnormal sperm morphology in mice. However, effects transmitted to the offspring following paternal exposure have not been reported previously. The maximum tolerated dose (MTD) was 7.5 mg kg(-1) body weight and this dose resulted in no deaths, although blood plasma cholinesterase activity was still decreased. Males were euthanized 4 weeks after an acute intraperitoneal injection of methamidophos (0.5, 3.75, 5.0, and 7.5 mg kg(-1) body wt) and the number of spermatids per gram testes and sperm morphology were analyzed. In this study, abnormal sperm morphology on a per group basis exhibited a dose-response significantly related to increased methamidophos exposure as indicated by regression analysis and a nested ANOVA (p < 0.0001). Preimplantation embryos that were conceived 6 weeks after paternal methamidophos exposure (5 mg kg(-1) body wt) exhibited a significant increase in cleavage arrest. Fertility of males was also affected as shown by a decrease in the number of two- to four-cell embryos per male (postexposure week 6) and an increase in the number of degenerated embryos (postexposure weeks 4-6). We conclude that methamidophos may have the potential to produce transmissible adverse embryonic effects following an acute paternal germline exposure.

Acetylcholinesterase↗

PubMed1995

Tumor suppressor genes as negative growth regulators in development and differentiation.

Tumor suppressor genes have received much attention for their roles in the development of human malignancies. However, their gene products (proteins) function as negative growth regulators and are highly expressed in many tissues during embryonic development, suggesting that they might function as critical proteins in differentiation and development. The evidence implicating tumor suppressor proteins in cellular differentiation and embryonic development will be presented with special attention to the neurofibromatosis 1, neurofibromatosis 2, and tuberous sclerosis 2 gene products.

Cell Cycle Proteins↗

PubMed1996

Lineage-specific morphogenesis in the developing pancreas: role of mesenchymal factors.

Pancreatic organogenesis has been a classic example of epitheliomesenchymal interactions. The nature of this interaction, and the way in which endocrine, acinar and ductal cell lineages are generated from the embryonic foregut has not been determined. It has generally been thought that mesenchyme is necessary for all aspects of pancreatic development. In addition islets have been thought to derive, at least in part, from ducts. We microdissected 11-day embryonic mouse pancreas and developed several culture systems for assays of differentiation: (i) on transparent filters; (ii) suspended in a collagen I gel; (iii) suspended in a basement membrane rich gel; (iv) under the renal capsule of an adult mouse. Epithelia were grown either with or without mesenchyme, and then assayed histologically and immunohistochemically. Epithelium with its mesenchyme (growth systems i-iv) always grew into fully differentiated pancreas (acinar, endocrine, adn ductal elements). In the basement membrane-rich gel, epithelium without mesenchyme formed ductal structures. Under the renal capsule of the adult mouse the epithelium without mesenchyme exclusively formed clusters of mature islets. These latter results represent the first demonstration of pure islets grown from early pancreatic precursor cells. In addition, these islets seemed not to have originated from ducts. We propose that the default path for growth of embryonic pancreatic epithelium is to form islets. In the presence of basement membrane constituents, however, the pancreatic analage epithelium appears to be programmed to form ducts. Mesenchyme seems not to be required for all aspects of pancreatic development, but rather only for the formation of acinar structures. In addition, the islets seem to form from early embryonic epithelium (which only express non-acinar genes). This formation occurs without any specific embryonic signals, and without any clear duct or acinus formation.

Animals↗

PubMed2006

Morphogenesis in the family Volvocaceae: different tactics for turning an embryo right-side out.

Green algae of the family Volvocaceae provide an unrivalled opportunity to analyze an evolutionary pathway leading from unicellularity to multicellularity with division of labor. One key step required for achieving multicellularity in this group was the development of a process for turning an embryo inside out: a morphogenetic process that is now known as "inversion," and that is a diagnostic feature of the group. Inversion is essential because at the end of its embryonic cleavage divisions, each volvocacean embryo contains all of the cells that will be present in an adult, but the flagellar ends of all cells are pointed toward the interior, rather than toward the exterior where they will need to be to function in locomotion. Inversion has been studied in greatest detail in Volvox carteri, but although all other volvocacean species have to struggle with the same awkward situation of being wrong-side out at the end of cleavage, they do it in rather different ways. Here, the inversion processes of six different volvocacean species (Gonium pectorale, Pandorina morum, Eudorina unicocca, Volvox carteri, Volvox tertius, and Volvox globator) are compared, in order to illustrate the variation in inversion patterns that exists within this family. The simplest inversion process occurs in the plate-shaped alga Gonium pectorale and the most complicated in the spherical alga Volvox globator. Gonium pectorale goes only from a concave-bowl shape to a slightly convex plate. In Volvox globator, the posterior hemisphere inverts completely before the anterior pole opens and the anterior hemisphere slides over the already-inverted posterior hemisphere; during both halves of this inversion process, the regions of maximum cell-sheet curvature move progressively, as radially symmetrical waves, along the posterior-anterior axis.

Cell Division↗

PubMed1990

The three postblastoderm cell cycles of Drosophila embryogenesis are regulated in G2 by string.

The string (stg) locus of Drosophila encodes a factor that is thought to trigger mitosis by activating the p34cdc2 protein kinase. stg is required for mitosis early in development and is transcribed in a dynamic pattern that anticipates the pattern of embryonic cell divisions. Here we show that differential cell cycle regulation during postblastoderm development (cell cycles 14-16) occurs in G2. We demonstrate that stg mRNA expressed from a heat shock promotor triggers mitosis, and an associated S phase, in G2 cells during these cycles. Hence, differential cell cycle timing at this developmental stage is controlled by stg. Finally, we use heat-induced stg expression to alter the normal pattern of embryonic mitoses. Surprisingly, the complex mitotic pattern evident during normal development is not essential for many features of pattern formation or for viability.

Animals↗

PubMed1989

Differentiation, maturation, and proliferation of macrophages in the mouse yolk sac: a light-microscopic, enzyme-cytochemical, immunohistochemical, and ultrastructural study.

Primitive macrophages first appear in the blood islands of the mouse yolk sac on the ninth day of gestation. After the tenth day of fetal life, these cells differentiate into fetal macrophages and become mature, with the development of intracellular organelles. They appear in the mesenchymal layer and further immigrate into the extraembryonic coelom. The fetal macrophages do not show any cytochemical peroxidase or 5'-nucleotidase activity, and they possess a marked proliferative capacity. Promonocytes or monocytes that have an incomplete ultrastructure emerge in the blood islands of the yolk sac a day after the occurrence of the fetal macrophages. These events suggest that fetal macrophages differentiate from primitive macrophages before the development of promonocytes or monocytes in the mouse yolk sac; they actively proliferate and are colonized into the embryonic tissues. These results also indicate that the ontogeny of the monocyte/macrophage is different in the early embryo compared with its later developmental stages.

5'-Nucleotidase↗

PubMed1995

Embryonic tissue differentiation in Caenorhabditis elegans requires dif-1, a gene homologous to mitochondrial solute carriers.

The dif-1 gene was identified in a general screen for maternal-effect embryonic lethal (Mel) mutants. dif-1 mutant embryos complete gastrulation and embryonic cell division normally, but then arrest development with only a small amount of tissue differentiation. Either maternal or zygotic dif-1 activity is sufficient for wild-type development. The temperature-sensitive period of a cold-sensitive dif-1 mutant shows that dif-1 activity is essential only for 3 h, corresponding to the major period of embryonic tissue differentiation, and is not required post-embryonically. The results point to a role for dif-1 in the maintenance of tissue differentiation in the developing embryo, but not for its initiation. Cloning and sequencing of the dif-1 gene revealed that its product is homologous to proteins in the mitochondrial carrier family. Although dif-1 activity is required only during embryogenesis, dif-1 RNA is expressed at all stages of development. In situ hybridization to embryos showed that dif-1 RNA is initially present in all cells of the embryo; this most likely corresponds to maternal dif-1 RNA. Later, the presumable zygotic dif-1 RNA is found only in the gut and hypodermis of the embryo. This tissue-specific expression raises the possibility that the dif-1 protein acts non-cell autonomously and that some communication or molecular transport dependent on DIF-1 takes place during embryonic tissue differentiation. dif-1 is the first mitochondrial carrier homologue known to be needed specifically for a developmental process.

Amino Acid Sequence↗

PubMed1988

Structural analysis of the mitotic cycle in pre-gastrula Xenopus embryos.

The long-known phenomenon of karyomere (chromosome vesicle) formation at early telophase of the nuclear cycle during early embryogenesis of a wide range of organisms including amphibians (Rubaschkin 1905; for review, see Richards 1917) was investigated in the early cleavage cycles of Xenopus laevis embryos before the mid blastula transition. Embryos were fixed and Epon embedded at successive time intervals and consecutive thick (3 micron) and ultrathin sections cut. Using conventional light microscopy at low magnification as well as phase and/or interference contrast video microscopy at high magnification, a substantial amount of information could be obtained from the analysis of optical sections in thick-sectioned material. In addition, details of the ultrastructural organization could be analysed from corresponding ultrathin sections by electron microscopy. The light microscopic analysis of serial thick sections allowed precise determination of the arrangement and sizes of telophase karyomere structures during the embryonic nuclear division cycle. It was found that small, widely spaced 1st order karyomeres fuse to larger (2nd order) karyomeres which then progressively exhibit lateral fusion of neighbouring karyomeres. The final coalescence of adjacent karyomeres marks the onset of the reorganization of the typical interphase nuclear structure. The data are discussed with regard to the occurrence of karyomeres during the embryonic nuclear cycle of arthropods, dipteran insects, and echinoderms as well as recent progress in the use of Xenopus egg extracts for in vitro assembly of nuclear structures around protein-free DNA.

Animals↗

PubMed2003

Distribution of keratin 8-containing cell clusters in mouse embryonic tongue: evidence for a prepattern for taste bud development.

The initiation of the morphogenesis of gustatory papillae is independent of innervation. To address the question of whether taste bud formation is associated with gustatory papilla morphogenesis, we examined developing tongues in mouse embryos from embryonic day 11 to birth. Despite the smooth morphological appearance of the lingual dorsal surface at 13 days of gestation, we observed embryonic taste bud primordia as discrete collections of cytokeratin 8-positive and elongated cells in epithelial placodes in the anterior tongue. In subsequent stages until birth, cytokeratin 8 continues to be expressed in embryonic taste buds distributed in punctuate patterns at regular intervals along rows that are symmetrically located on both sides of the median sulcus in the dorsal anterior developing tongue. Embryonic taste buds were observed in the developing circumvallate papillae from 15.5 days of gestation until birth. The dorsal epithelium of the anterior tongue is not innervated when embryonic taste buds first occur. The increased numbers of embryonic taste buds in developing fungiform papillae until birth are not correlated with the neural invasion of the epithelium. Thus, taste buds occur prenatally more likely independently of the innervation.

Animals↗

PubMed2004

Fgf18 is required for embryonic lung alveolar development.

Fgf18 is abundantly expressed in mouse embryonic lungs. To elucidate the roles of Fgf18 in mouse embryonic lung development, we examined the Fgf18-/- embryonic lungs. Although the sizes of the Fgf18-/- lungs were a little smaller in appearance than those of wild-type lungs, neither proximal nor distal airway branching in the Fgf18-/- lungs was impaired. However, the Fgf18-/- lungs at E18.5 had reduced alveolar space, thicker interstitial mesenchymal compartments, and many embedded capillaries. Cell proliferation in the Fgf18-/- lungs was also transiently reduced around E17.5, although the expression of marker genes for lung epithelial cells in the Fgf18-/- lungs was not impaired. The present findings indicate that the Fgf18 plays roles in lung alveolar development during late embryonic lung development stages. The cell proliferation during the terminal saccular stage stimulated by Fgf18 might play roles in the remodeling of the distal lung.

Animals↗