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PubMed1998

Temporal patterns of embryonic gene expression and their dependence on oogenetic factors.

Successful development of a fertilized egg beyond early cleavage divisions requires the de novo initiation and subsequent regulation of embryonic transcription. The egg provides the specialized environment within which the newly formed zygotic nucleus initiates its developmental program and as a result plays an obligatory role in its regulation. Although the precise timing of the onset of embryonic transcription in mammals varies during early cleavage divisions, several common elements exist. In the present essay we review the current literature on the timing and control of embryonic gene expression in mammals, and discuss recent findings from our laboratory on gene expression patterns in bovine embryos and their relation to other species, and zygotic gene activation (ZGA). Lastly, we discuss the putative role of maternally inherited factors in conferring developmental competence to the blastocyst stage, and a method to identify such factors present in oocytes as mRNA.

Animals↗
PubMed1993

Reduction of naturally-occurring cell death by kainic acid in the retina of chicken embryos.

The development of the nervous system can be modified by the application of transmitter agonist or antagonists. Therefore, the growth of the retina in chicken embryos was studied after injection of the excitatory amino acid, kainate, during the second half of the pre-hatching period. Quantitative anatomical and biochemical investigations were undertaken. In the kainate treated animals the volume of the retina and its different layers was seen to exceed significantly those of control retinas from the 14th ontogenetic day onwards. This was accompanied by a total increase in cell number as well as DNA content on the 18th day of ontogenesis, though the mitotic activity during this period was comparable to that in the control group, and signs of degenerative processes ("rosettes") were found. Therefore, we conclude that the excitatory amino acid, kainate, reduces the naturally occurring cell death in the embryonic retina.

Animals↗
PubMed2001

The Snail protein family regulates neuroblast expression of inscuteable and string, genes involved in asymmetry and cell division in Drosophila.

Delaminated neuroblasts in Drosophila function as stem cells during embryonic central nervous system development. They go through repeated asymmetric divisions to generate multiple ganglion mother cells, which divide only once more to produce postmitotic neurons. Snail, a zinc-finger transcriptional repressor, is a pan-neural protein, based on its extensive expression in neuroblasts. Previous results have demonstrated that Snail and related proteins, Worniu and Escargot, have redundant and essential functions in the nervous system. We show that the Snail family of proteins control central nervous system development by regulating genes involved in asymmetry and cell division of neuroblasts. In mutant embryos that have the three genes deleted, the expression of inscuteable is significantly lowered, while the expression of other genes that participate in asymmetric division, including miranda, staufen and prospero, appears normal. The deletion mutants also have much reduced expression of string, suggesting that a key component that drives neuroblast cell division is abnormal. Consistent with the gene expression defects, the mutant embryos lose the asymmetric localization of prospero RNA in neuroblasts and lose the staining of Prospero protein that is normally present in ganglion mother cells. Simultaneous expression of inscuteable and string in the snail family deletion mutant efficiently restores Prospero expression in ganglion mother cells, demonstrating that the two genes are key targets of Snail in neuroblasts. Mutation of the dCtBP co-repressor interaction motifs in the Snail protein leads to reduction of the Snail function in central nervous system. These results suggest that the Snail family of proteins control both asymmetry and cell division of neuroblasts by activating, probably indirectly, the expression of inscuteable and string.

Animals↗
PubMed1987

A quantitative histological study of cell division and changes in cell number in the meningeal sheath of the embryonic human optic nerve.

Mitotic cells are present in all layers of the meninges of the human optic nerve between 8 and 18 weeks post-conception. The number of meningeal cells per section remains constant between 8 and 12 weeks before rising rapidly from 234 at 12 weeks to 747 at 18 weeks. The mitotic index is only 0.17% at 8 weeks but rises to 1.02% at 10 weeks before falling gradually to 0.29% at 18 weeks. A comparison of the results of this study with a previous one on gliogenesis in the same nerves (Sturrock, 1975) leads to the tentative conclusion that mitotic activity in the layers of the meninges is probably sufficient to account for the increase in meningeal cell number between 8 and 18 weeks. The substantial increase in thickness of the meninges found between 14 and 15 weeks is due to a large increase in the amount of collagen in the developing dural layer rather than the modest increase in cell number. During mitosis meningeal cells do not retract their processes and cell division usually occurs tangentially.

Cell Count↗
PubMed2000

A critical role of sterols in embryonic patterning and meristem programming revealed by the fackel mutants of Arabidopsis thaliana.

Here we report a novel Arabidopsis dwarf mutant, fackel-J79, whose adult morphology resembles that of brassinosteroid-deficient mutants but also displays distorted embryos, supernumerary cotyledons, multiple shoot meristems, and stunted roots. We cloned the FACKEL gene and found that it encodes a protein with sequence similarity to both the human sterol reductase family and yeast C-14 sterol reductase and is preferentially expressed in actively growing cells. Biochemical analysis indicates that the fk-J79 mutation results in deficient C-14 sterol reductase activity, abnormal sterol composition, and reduction of brassinosteroids (BRs). Unlike other BR-deficient mutants, the defect of hypocotyl elongation in fk-J79 cannot be corrected by exogenous BRs. The unique phenotypes and sterol composition in fk-J79 indicate crucial roles of sterol regulation and signaling in cell division and cell expansion in embryonic and post-embryonic development in plants.

Alleles↗
PubMed2003

The emerging phenotype of the testicular carcinoma in situ germ cell.

This review summarises the existing knowledge on the phenotype of the carcinoma in situ (CIS) cell. CIS is a common pre-invasive precursor of testicular germ cell tumours of adolescents and young adults. These tumours display a variety of histological forms. Classical seminoma proliferates along the germ cell lineage, whereas embryonal carcinoma retains embryonic features and readily differentiates into teratomas that resemble various somatic cell lineages. A thorough review of the gene expression in CIS cells in comparison to normal testicular germ cells and overt tumours supports the view that CIS is a common precursor for both tumour types. Impaired cell differentiation resulting in a partial retention of the embryonic features, associated with an increasing genomic instability may be responsible for a remarkable phenotypic heterogeneity of CIS cells. Depending on the degree of differentiation and pluripotency, CIS cells found in adult patients seem to be predestined for further malignant progression into one or the other of the two main types of overt tumours. A new concept of phenotypic continuity of differentiation of germ cells along germinal lineage with a gradual loss of embryonic features based on the analysis of gene expression in all types of germ cells during their ontogeny is presented in this review. The data point out that despite the phenotypic continuum of gene expression, there are two periods of rapid changes of gene expression: first at the transition from primordial germ cells to pre-spermatogonia, and later during the pubertal switch from the mitotic to meiotic cell division. The persistent expression of embryonic traits in CIS cells, and the high expression of the cell cycle regulators that are typical of mitotic germ cells support our long-standing hypothesis that CIS cells originate from primordial germ cells or gonocytes and not from germ cells in the adult testis.

Adolescent↗
PubMed1998

Atypical protein kinase C cooperates with PAR-3 to establish embryonic polarity in Caenorhabditis elegans.

Asymmetric cell divisions, critically important to specify cell types in the development of multicellular organisms, require polarized distribution of cytoplasmic components and the proper alignment of the mitotic apparatus. In Caenorhabditis elegans, the maternally expressed protein, PAR-3, is localized to one pole of asymmetrically dividing blastomeres and is required for these asymmetric divisions. In this paper, we report that an atypical protein kinase C (PKC-3) is essential for proper asymmetric cell divisions and co-localizes with PAR-3. Embryos depleted of PKC-3 by RNA interference die showing Par-like phenotypes including defects in early asymmetric divisions and mislocalized germline-specific granules (P granules). The defective phenotypes of PKC-3-depleted embryos are similar to those exhibited by mutants for par-3 and another par gene, par-6. Direct interaction of PKC-3 with PAR-3 is shown by in vitro binding analysis. This result is reinforced by the observation that PKC-3 and PAR-3 co-localize in vivo. Furthermore, PKC-3 and PAR-3 show mutual dependence on each other and on three of the other par genes for their localization. We conclude that PKC-3 plays an indispensable role in establishing embryonic polarity through interaction with PAR-3.

Animals↗
PubMed1991

Does trans-lesion synthesis explain the UV-radiation resistance of DNA synthesis in C. elegans embryos?

Over 10-fold larger fluences were required to inhibit both DNA synthesis and cell division in wild-type C. elegans embryos as compared with other model systems or C. elegans rad mutants. In addition, unlike in other organisms, the molecular weight of daughter DNA strands was reduced only after large, superlethal fluences. The molecular weight of nascent DNA fragments exceeded the interdimer distance by up to 19-fold, indicating that C. elegans embryos can replicate through non-instructional lesions. This putative trans-lesion synthetic capability may explain the refractory nature of UV radiation on embryonic DNA synthesis and nuclear division in C. elegans.

Animals↗
PubMed2003

Yeast DNA polymerase zeta (zeta) is essential for error-free replication past thymine glycol.

DNA polymerase zeta (Polzeta) promotes the mutagenic bypass of DNA lesions in eukaryotes. Genetic studies in Saccharomyces cerevisiae have indicated that relative to the contribution of other pathways, Polzeta makes only a modest contribution to lesion bypass. Intriguingly, however, disruption of the REV3 gene, which encodes the catalytic subunit of Polzeta, causes early embryonic lethality in mice. Here, we present genetic and biochemical evidence for the requirement of yeast Polzeta for predominantly error-free replication past thymine glycol (Tg), a DNA lesion formed frequently by free radical attack. These results raise the possibility that, as in yeast, in higher eukaryotes also, Polzeta makes a major contribution to the replicative bypass of Tgs as well as other lesions that block synthesis by replicative DNA polymerases. Such a preeminent role of Polzeta in lesion bypass would ensure that rapid cell divisions continue unabated during early embryonic development, thereby minimizing the generation of DNA strand breaks, chromosome aberrations, and the ensuing apoptotic response.

Base Pairing↗
PubMed2004

Survivin: a bifunctional inhibitor of apoptosis protein.

Survivin is a recently discovered protein belonging to the inhibitor of apoptosis (IAP) gene family. IAP molecules are characterized by both the presence of a zinc-binding fold termed the baculoviral IAP repeat and the ability to suppress apoptosis. In addition to inhibiting apoptosis, survivin is essential for proper cell division. Survivin is expressed during embryonal development but is absent in most normal, terminally differentiated tissues. Survivin is also upregulated in a variety of human cancers, and its expression in tumors is associated with a more aggressive phenotype, shorter survival times, and a decreased response to chemotherapy. The exact mechanism behind the ability of survivin to inhibit apoptosis is still unclear. Furthermore, it is not known why this protein is upregulated in cancer. The purpose of this article is to provide an overview of the current knowledge of survivin, including its role in cell division and its expression in normal and neoplastic tissues. Although much of the current research in this field is focused on human medicine, this area also has potential significance for veterinary species.

Animals↗
PubMed1995

Vitrification of human oocytes following minimal exposure to cryoprotectants; initial studies on fertilization and embryonic development.

Investigations were made into the low temperature preservation of pre-ovulatory human oocytes by vitrification using a method of brief exposure of the oocytes to the vitrification solution at room temperature. Assessments of morphological survival, fertilization and embryonic development were recorded. All those oocytes exposed to the vitrification solution alone were morphologically normal and 86% of them were fertilized after incubation with spermatozoa. All the fertilized ova (86%) underwent cell division. Following cooling to -196 degrees C, morphological survival (65%) and fertilization (45%) rates remained high. However, in all vitrified oocytes, embryonic cell division and further development were inhibited. From our study it appears that fresh human oocytes can be vitrified using only brief exposure to cryoprotective agents and survive to undergo fertilization. However, progress remains to be made in achieving further embryonic development.

Cell Survival↗
PubMed1991

Cell division is required for expression of v-myc transforming properties in chicken embryonic neuroretina cells.

We previously reported that avian retroviruses carrying the v-myc oncogene alone fail to induce sustained proliferation and transformation of non-dividing chicken neuroretina (CNR) cells from 7-day-old embryos. However, v-myc is capable of transforming CNR cells which have been induced to multiply by the v-mil oncogene. These results suggest that entry into the cell cycle is required for the transformation of CNR cells by v-myc. To further assess the role of cell division, we investigated the transforming properties of v-myc in CNR cells conditionally induced to divide by the v-src gene or by modified culture conditions. We show that v-myc transforms CNR cells infected with Rous sarcoma virus mutants which induce cell proliferation in the absence of transformation. Expression of these transforming properties in CNR cells infected with temperature-sensitive v-src mutants depends on the continuous mitogenic activity of p60v-src. We also report that v-myc is able to transform CNR cells and to increase their growth potential under culture conditions which allow transient multiplication of uninfected cells. However, these v-myc-transformed cells rapidly cease to divide when returned to culture conditions that restrict the growth of normal cells. Taken together, these results indicate that transformation of CNR cells by the v-myc oncogene continuously depends on their ability to enter the cell cycle.

Animals↗
PubMed1999

Drosophila embryonic pattern repair: how embryos respond to cyclin E-induced ectopic division.

The Drosophila melanogaster embryo ordinarily undergoes thirteen cycles of rapid syncytial division followed by three rounds of cellular division for most cells. Strict regulation of the number of divisions is believed to be essential for normal patterning and development. To determine how the embryo responds to hyperplastic growth, we have examined epidermal development in embryos that experience additional rounds of mitosis as the result of ectopic Cyclin E expression. We observed that the cell density in the epidermis nearly doubled within 1 hour of Cyclin E induction. The spacing and width of the ENGRAILED and wingless stripes was unchanged, but the cell density within the stripes was increased. By 4 hours after Cyclin E induction, the cell density had returned to almost normal values. The embryos developed, albeit more slowly, to produce viable larvae and adults. The excess cells were removed by apoptosis in a reaper-dependent fashion as evidenced by increased reaper expression. Embryos lacking cell death in the abdomen exhibited changes in ENGRAILED expression. In addition, germband retraction and dorsal closure were slower than normal. Ectopic Cyclin E expression in cell-death-deficient embryos exacerbated the germband retraction and ENGRAILED-expression defects.

Animals↗
PubMed2006

Orientation of endothelial cell division is regulated by VEGF signaling during blood vessel formation.

New blood vessel formation requires the coordination of endothelial cell division and the morphogenetic movements of vessel expansion, but it is not known how this integration occurs. Here, we show that endothelial cells regulate division orientation during the earliest stages of blood vessel formation, in response to morphogenetic cues. In embryonic stem (ES) cell-derived vessels that do not experience flow, the plane of endothelial cytokinesis was oriented perpendicular to the vessel long axis. We also demonstrated regulated cleavage orientation in vivo, in flow-exposed forming retinal vessels. Daughter nuclei moved away from the cleavage plane after division, suggesting that regulation of endothelial division orientation effectively extends vessel length in these developing vascular beds. A gain-of-function mutation in VEGF signaling increased randomization of endothelial division orientation, and this effect was rescued by a transgene, indicating that regulation of division orientation is a novel mechanism whereby VEGF signaling affects vessel morphogenesis. Thus, our findings show that endothelial cell division and morphogenesis are integrated in developing vessels by flow-independent mechanisms that involve VEGF signaling, and this cross talk is likely to be critical to proper vessel morphogenesis.

Animals↗
PubMed1997

Relationship between timing of development, morula morphology, and cell allocation to inner cell mass and trophectoderm in in vitro-produced bovine embryos.

Noninvasive measurements of bovine embryo quality, such as timing of cleavage, morula morphology, blastocyst formation, and hatching ability, were linked with the number of inner cell mass (ICM) cells and trophectoderm (TE) cells of the resulting embryos. First, it was confirmed that fast-cleaving embryos proved to have significantly higher chances to reach advanced developmental stages vs. intermediate and slow cleavers (P = 0.01). They also showed significantly less fragmentation at the morula stage, implying the presence of more excellent morulae among fast-cleaving embryos (P < 0.05). Second, the quality of hatched blastocysts, resulting from morulae of different morphological grades, was examined by differential staining. The total cell and ICM cell numbers were significantly lower for hatched blastocysts developed from poor morulae compared to hatched blastocysts developed from excellent, good, or fair morulae. However, hatched blastocysts with < 10 ICM cells were seen in embryos belonging to all four morphological scores. Finally, it was found that timing of first cleavage was not significantly correlated with timing of blastocyst formation or with cell number of blastocysts. Timing of blastocyst formation, however, was significantly correlated with cell number: day 8 blastocysts had significantly lower total cell and ICM cell numbers than day 6 and day 7 blastocysts (P < 0.001). These results suggest that the quality of in vitro-produced bovine embryos is very variable and cannot be linked with a single criterion such as embryo morphology and/or hatching ability. Timing of blastocyst formation was the most valuable criterion with regard to embryonic differentiation.

Animals↗