Establishment of an in vitro culture system for chicken preblastodermal cells

To develop an alternative source for chicken pluripotent cells, we examined (1) whether undifferentiated preblastodermal cells could be subcultured in vitro for an extended period and (2) how subculturing affected the physiological properties of preblastodermal cells. The average number of preblastodermal cells was 2,397 in stage V embryos and 36,345 in stage VII embryos; stage X embryos had an average of 53,857 blastodermal cells. The average cell size decreased significantly (70.63-18.83 microm in diameter; P < 0.0001) as the embryo grew; this was closely related to a reduction in the size and number of lipid vesicles in the cell cytoplasm. The culture conditions were optimized for the stage V preblastodermal cells and the control stage X blastodermal cells. On STO feeder cells, the preblastodermal cells achieved stable growth in vitro only in HES medium or a mixed medium of the Knockout DMEM and HES media. However, more than 10 passages of preblastodermal cells at intervals of 3-4 days was possible only by using the Knockout/HES mixed medium and BRL cell-conditioned HES medium for the primary cultures and subcultures, respectively. Colony-forming preblastodermal cells had well-delineated cytoplasm, which was positively stained for stem cell-specific markers by anti-stage-specific embryo antigen-1 antibody, periodic acid-Schiff's solution, and alkaline phosphatase. When preblastodermal cells with or without culturing were transferred into the blastodermal cavity of stage X embryos, only in vitro-cultured preblastodermal cells at stage V (4/5 = 80%) and stage VII (2/8 = 25%) induced somatic chimerism in recipient chickens. In conclusion, undifferentiated preblastodermal cells could be subcultured, and only the colony-forming preblastodermal cells that stained positively for stem cell markers could induce somatic chimerism.

The secretory membrane system in the Drosophila syncytial blastoderm embryo exists as functionally compartmentalized units around individual nuclei

Drosophila melanogaster embryogenesis begins with 13 nuclear division cycles within a syncytium. This produces >6,000 nuclei that, during the next division cycle, become encased in plasma membrane in the process known as cellularization. In this study, we investigate how the secretory membrane system becomes equally apportioned among the thousands of syncytial nuclei in preparation for cellularization. Upon nuclear arrival at the cortex, the endoplasmic reticulum (ER) and Golgi were found to segregate among nuclei, with each nucleus becoming surrounded by a single ER/Golgi membrane system separate from adjacent ones. The nuclear-associated units of ER and Golgi across the syncytial blastoderm produced secretory products that were delivered to the plasma membrane in a spatially restricted fashion across the embryo. This occurred in the absence of plasma membrane boundaries between nuclei and was dependent on centrosome-derived microtubules. The emergence of secretory membranes that compartmentalized around individual nuclei in the syncytial blastoderm is likely to ensure that secretory organelles are equivalently partitioned among nuclei at cellularization and could play an important role in the establishment of localized gene and protein expression patterns within the early embryo.

Mutations of the Drosophila zinc finger-encoding gene vielfältig impair mitotic cell divisions and cause improper chromosome segregation

We describe the molecular characterization and function of vielfältig (vfl), a X-chromosomal gene that encodes a nuclear protein with six Krüppel-like C2H2 zinc finger motifs. vfl transcripts are maternally contributed and ubiquitously distributed in eggs and preblastoderm embryos, excluding the germline precursor cells. Zygotically, vfl is expressed strongly in the developing nervous system, the brain, and in other mitotically active tissues. Vfl protein shows dynamic subcellular patterns during the cell cycle. In interphase nuclei, Vfl is associated with chromatin, whereas during mitosis, Vfl separates from chromatin and becomes distributed in a granular pattern in the nucleoplasm. Functional gain-of-function and lack-of-function studies show that vfl activity is necessary for normal mitotic cell divisions. Loss of vfl activity disrupts the pattern of mitotic waves in preblastoderm embryos, elicits asynchronous DNA replication, and causes improper chromosome segregation during mitosis.

Ultrastructural and Immunohistochemical Characterization of the Bovine Epiblast1

The epiblast represents the final embryonic founder cell population with the potential for giving rise to all cell types of the adult body. The pluripotency of the epiblast is lost during the process of gastrulation. Large animal species have a lack of specific markers for pluripotency. The aim of the present study was to characterize the bovine epiblast cell population and to provide such markers. Bovine Day 12 and Day 14 embryos were processed for transmission-electron microscopy or immunohistochemistry. In Day 12 embryos, two cell populations of the epiblast were identified: one constituting a distinctive basal layer apposing the hypoblast, and one arranged inside or above the former layer, including cells apposing the Rauber layer. Immunohistochemically, staining for the octamer-binding transcription factor 4 (OCT4, also known as POU5F1), revealed a specific and exclusive staining of nuclei of the complete epiblast. Colocalization of vimentin and OCT4 was demonstrated. Only trophectodermal cells stained for alkaline phosphatase. Staining for the proliferation marker Ki-67 was localized to most nuclei throughout the epiblast. A continuous staining for zonula occludens-1 protein was found between cells of the trophectoderm and hypoblast but was not evident in the epiblast. A basement membrane, detected by staining for laminin, formed a "cup-like" structure in which the epiblast was located. The ventrolateral sides of the cup appeared to be incomplete. In conclusion, the bovine epiblast includes at least two cell subpopulations, and OCT4 was shown, to our knowledge for the first time, to be localized exclusively to epiblast cells in this species.

UV laser cross-linking: a real-time assay to study dynamic protein/DNA interactions during chromatin remodeling

We describe the use of laser ultraviolet (UV) cross-linking to study the interaction of transcription factors with in vitro assembled chromatinized DNA templates in real time. Because the laser source delivers a high density of photons in a single ns pulse, the cross-linking reaction is completed in less than 1 microseconds, allowing the investigator to freeze rapid dynamic changes in protein-DNA interactions. Using this approach, we have sampled the dynamic equilibrium of the glucocorticoid receptor (GR) and the chromatin remodeling complex (SWI/SNF) during adenosine triphosphate (ATP)-dependent chromatin remodeling on a chromatinized mouse mammary tumor virus promoter in vitro. UV laser cross-linking shows that the GR and SWI/SNF complex undergoes a periodic binding and displacement event during the process of chromatin remodeling. The assay provides unique information regarding the equilibrium of protein-DNA interactions in real time and can be easily adapted to study the dynamic events in the assembly and disassembly of other multiprotein complexes on chromatin or DNA templates.

Primary sex ratios in birds: problems with molecular sex identification of undeveloped eggs

Sex allocation studies seek to ascertain whether mothers manipulate offspring sex ratio prior to ovulation. To do so, DNA for molecular sexing should be collected as soon after conception as possible, but instead neonates are usually sampled. Here, we aim to identify and quantify some of the problems associated with using molecular techniques to identify the sex of newly laid avian eggs. From both fertilized and unfertilized chicken (Gallus gallus) eggs, we sampled (1) the blastoderm/disc, (2) vitelline membrane and (3) a mixture of (1) and (2). Thus, we replicated scenarios under which contaminated samples are taken and/or unfertilized eggs are not identified as such and are sampled. We found that two commonly used molecular sexing tests, based on the CHD-1 genes, differed in sensitivity, but this did not always predict their ability to sex egg samples. The vitelline membrane was a considerable source of maternal and probably paternal contamination. Fertile eggs were regularly assigned the wrong sex when vitelline membrane contaminated the blastoderm sample. The membrane of unfertilized eggs was always female, i.e. maternal DNA had been amplified. DNA was amplified from 47 to 63% of unfertilized blastodiscs, even though it was highly unlikely that DNA from a single haploid cell could be amplified reliably using these polymerase chain reaction (PCR) techniques. Surprisingly, the blastodiscs were identified as both males and females. We suggest that in these cases only maternal DNA was amplified, and that 'false' males, Z not ZZ, were detected. This was due to the reduced ability of both sets of primers to anneal to the W chromosome compared to the Z chromosome at low DNA concentrations. Overall, our data suggested that estimates of primary sex ratios based on newly laid eggs will be appreciably inaccurate.

Disruption of vitellogenin gene function in adult honeybees by intra-abdominal injection of double-stranded RNA

BACKGROUND

The ability to manipulate the genetic networks underlying the physiological and behavioural repertoires of the adult honeybee worker (Apis mellifera) is likely to deepen our understanding of issues such as learning and memory generation, ageing, and the regulatory anatomy of social systems in proximate as well as evolutionary terms. Here we assess two methods for probing gene function by RNA interference (RNAi) in adult honeybees.

RESULTS

The vitellogenin gene was chosen as target because its expression is unlikely to have a phenotypic effect until the adult stage in bees. This allowed us to introduce dsRNA in preblastoderm eggs without affecting gene function during development. Of workers reared from eggs injected with dsRNA derived from a 504 bp stretch of the vitellogenin coding sequence, 15% had strongly reduced levels of vitellogenin mRNA. When dsRNA was introduced by intra-abdominal injection in newly emerged bees, almost all individuals (96%) showed the mutant phenotype. An RNA-fragment with an apparent size similar to the template dsRNA was still present in this group after 15 days.

CONCLUSION

Injection of dsRNA in eggs at the preblastoderm stage seems to allow disruption of gene function in all developmental stages. To dissect gene function in the adult stage, the intra-abdominal injection technique seems superior to egg injection as it gives a much higher penetrance, it is much simpler, and it makes it possible to address genes that are also expressed in the embryonic, larval or pupal stages.

Origin of primordial germ cells in the prestreak chick embryo

The temporal and spatial pattern of segregation of the avian germline from the formation of the area pellucida to the beginning of primitive streak formation (stages VII-XIV, EG&K) was investigated using the culture of whole embryos and central and peripheral embryo fragments on vitelline membranes at stages VII-IX, immunohistological analysis of whole mount embryos and sections with monoclonal antibodies MC-480 against stage-specific embryonic antigen-1 (SSEA-1) and EMA-1, and with the culture of dispersed blastoderms at stages IX-XIV with and without on STO feeder layer. Whole embryos at intrauterine stages developed up to the formation of the primitive streak despite the absence of area pellucida expansion. Primordial germ cells (PGCs) appeared in the cultures of whole embryos and only in central fragments containing a partially formed area pellucida at stages VII-IX. When individual stage IX-XIV embryos were dispersed and cultured without a feeder layer, 25-45 PGCs/embryo were detected only with stage X-XIV, but not with stage IX blastoderms. However, the culture of dispersed cells from the area pellucida of stages IX-XIII on STO feeder layers yielded about 150 PGCs/embryo. The carbohydrate epitopes recognized by anti-SSEA-1 and EMA-1 first appeared at stage X on cells in association with polyingressing cells on the ventral surface of the epiblast and later on the dorsal surface of the hypoblast. The SSEA-1-positive hypoblast cells gave rise to chicken PGCs when cultured on a feeder layer of quail blastodermal cells. From these observations, we propose that the segregation and development of avian germline is a gradual, epigenetic process associated with the translocation of SSEA-1/EMA-1-positive cells from the ventral surface of the area pellucida at stage X to the dorsal side of the hypoblast at stages XI-XIV.

Mutations in centrosomin reveal requirements for centrosomal function during early Drosophila embryogenesis

BACKGROUND

Although centrosomes serve as the primary organizing centers for the microtubule-based cytoskeleton in animal cells, various studies question the requirements for these organelles during the formation of microtubule arrays and execution of microtubule-dependent processes. Using a genetic approach to interfere with centrosomal function, we present an assessment of this issue, in the context of early embryogenesis of the fruit fly Drosophila melanogaster.

RESULTS

We identified mutant alleles of the centrosomin (cnn) locus, which encodes a core component of centrosomes in Drosophila. The cnn mutant flies were viable but sterile. The normal course of early embryonic development was arrested in all progeny of cnn mutant females. Our analysis identified a failure to form functional centrosomes and spindle poles as the primary mutant phenotype of cnn embryos. Various aspects of early development that are dependent on cytoskeletal control were disrupted in cnn mutant embryos. In particular, structural rearrangements of cortical microfilaments were strongly dependent on proper centrosomal function.

CONCLUSIONS

Centrosomin is an essential core component of early embryonic centrosomes in Drosophila. Microtubule-dependent events of early embryogenesis display differential requirements for centrosomal function.

The presence of transcription factors in chicken albumin, yolk and blastoderm

Embryonic development is determined by preset intrinsic programs and extrinsic signals. To explore the possibility that transcription factors are present at the onset of development, preparations of yolk, albumin, and blastoderm from unfertilized and fertilized white Leghorn chicken eggs were screened by a panel of 16 transcription factor antibodies with Western blot techniques. Yolk was positive for 13 transcription factors, whereas blastoderm was positive for 10, and albumin was positive for 5. In yolk, several transcription factors, GATA-2, E2F-1, MyoD, and TFIID, were developmentally regulated. These results indicate that intracellular yolk and extracellular albumin contain transcription factors which presumably influence early chick embryonic development from prefertilization to the late blastoderm stage. Thus, the utility of preset maternal transcription factors within yolk and albumin complement maternally derived mRNA to determine the early development of the zygote.

Structural and functional analysis of chromatin assembled from defined histones

In this review we describe how the extract-mediated chromatin assembly system derived from preblastoderm Drosophila embryos can be modified to assemble chromatin from defined histones. This approach combines the advantages of assembling (i) chromatin templates from homogeneous histones with (ii) an assembly system that generates chromatin with physiological nucleosome spacing and density and that contains the biological complexity of in vivo chromatin. We have used this technique to assemble nonacetylated and hyperacetylated histones into chromatin (K. P. Nightingale, R. Wellinger, J. Sogo, and P. B. Becker, 1998, EMBO J. 17, 2865-2876; W. A. Krajewski and P. B. Becker, 1998, Proc. Natl. Acad. Sci. USA 95, 1540-1545), and use this as an example to detail the structural and transcriptional assays used to compare and characterize these chromatin templates. The application of this procedure to assemble chromatin from recombinant histones should facilitate a wide variety of studies on the role(s) of histone mutants and variants.

The distribution of polycomb-group proteins during cell division and development in Drosophila embryos: impact on models for silencing

The subcellular three-dimensional distribution of three polycomb-group (PcG) proteins-polycomb, polyhomeotic and posterior sex combs-in fixed whole-mount Drosophila embryos was analyzed by multicolor confocal fluorescence microscopy. All three proteins are localized in complex patterns of 100 or more loci throughout most of the interphase nuclear volume. The rather narrow distribution of the protein intensities in the vast majority of loci argues against a PcG-mediated sequestration of repressed target genes by aggregation into subnuclear domains. In contrast to the case for PEV repression (Csink, A.K., and S. Henikoff. 1996. Nature. 381:529-531), there is a lack of correlation between the occurrence of PcG proteins and high concentrations of DNA, demonstrating that the silenced genes are not targeted to heterochromatic regions within the nucleus. There is a clear distinction between sites of transcription in the nucleus and sites of PcG binding, supporting the assumption that most PcG binding loci are sites of repressive complexes. Although the PcG proteins maintain tissue-specific repression for up to 14 cell generations, the proteins studied here visibly dissociate from the chromatin during mitosis, and disperse into the cytoplasm in a differential manner. Quantitation of the fluorescence intensities in the whole mount embryos demonstrate that the dissociated proteins are present in the cytoplasm. We determined that <2% of PH remains attached to late metaphase and anaphase chromosomes. Each of the three proteins that were studied has a different rate and extent of dissociation at prophase and reassociation at telophase. These observations have important implications for models of the mechanism and maintenance of PcG- mediated gene repression.

Misexpression of chick Vg1 in the marginal zone induces primitive streak formation

In the chick embryo, the primitive streak is the first axial structure to develop. The initiation of primitive streak formation in the posterior area pellucida is influenced by the adjacent posterior marginal zone (PMZ). We show here that chick Vg1 (cVg1), a member of the TGFbeta family of signalling molecules whose homolog in Xenopus is implicated in mesoderm induction, is expressed in the PMZ of prestreak embryos. Ectopic expression of cVg1 protein in the marginal zone chick blastoderms directs the formation of a secondary primitive streak, which subsequently develops into an ectopic embryo. We have used cell marking techniques to show that cells that contribute to the ectopic primitive streak change fate, acquiring two distinct properties of primitive streak cells, defined by gene expression and cell movements. Furthermore, naive epiblast explants exposed to cVg1 protein in vitro acquire axial mesodermal properties. Together, these results show that cVg1 can mediate ectopic axis formation in the chick by inducing new cell fates and they permit the analysis of distinct events that occur during primitive streak formation.

Expression and sequence analysis of the Drosophila blastoderm-specific gene bsg25A

By differential screening of a genomic library, we have cloned a gene expressed specifically during the blastoderm stage of Drosophila embryogenesis. Northern blot analysis and in situ hybridization to embryos reveal that the transcript is maximally expressed during the late syncytial blastoderm stage, disappears rapidly during the cellular blastoderm stage and is not detected at any other point in the Drosophila life cycle. On the basis of its temporally restricted expression and its polytene chromosomal map position at 25A1,2, we have designated this gene blastoderm-specific gene 25A (bsg25A). bsg25A encodes a novel protein of 23 kDa.

Manipulation of blastodermal cells

Blastodermal cells isolated from newly laid, unincubated eggs are virtually uncommitted cells that exhibit many of the properties of pluripotential stem cells. They can be transferred from donor to recipient embryos and contribute to both somatic tissues and the germline. Blastodermal cells that have been maintained in culture for 7 d express the epitopes ECMA-7 and SSEA-1, which are also expressed by mouse embryonic stem cells. After culture for up to at least 7 d, blastodermal cells retain the ability to differentiate into somatic tissues and the germline both in vivo and in vitro. Proliferation in the absence of differentiation of blastodermal cells is stimulated by the presence of Leukemia Inhibitory Factor (LIF) and other ligands that interact with the gp130 receptor, and differentiation is stimulated by exposure to retinoic acid. Blastodermal cells also possess high levels of telomerase activity, which is shared by immortalized cells and cells within the germline. Blastodermal cells can be transfected and will express foreign genes both in vivo and in vitro. Transfected cells can be isolated by fluorescence activated cell sorting and can be cryopreserved without losing their ability to contribute to either somatic tissues or the germline. These properties of blastodermal cells make them ideal vectors for introducing genetic modifications to the germline.

Control of germ-band retraction in Drosophila by the zinc-finger protein HINDSIGHT

Drosophila embryos lacking hindsight gene function have a normal body plan and undergo normal germ-band extension. However, they fail to retract their germ bands. hindsight encodes a large nuclear protein of 1920 amino acids that contains fourteen C2H2-type zinc fingers, and glutamine-rich and proline-rich domains, suggesting that it functions as a transcription factor. Initial embryonic expression of hindsight RNA and protein occurs in the endoderm (midgut) and extraembryonic membrane (amnioserosa) prior to germ-band extension and continues in these tissues beyond the completion of germ-band retraction. Expression also occurs in the developing tracheal system, central and peripheral nervous systems, and the ureter of the Malpighian tubules. Strikingly, hindsight is not expressed in the epidermal ectoderm which is the tissue that undergoes the cell shape changes and movements during germ-band retraction. The embryonic midgut can be eliminated without affecting germ-band retraction. However, elimination of the amnioserosa results in the failure of germ-band retraction, implicating amnioserosal expression of hindsight as crucial for this process. Ubiquitous expression of hindsight in the early embryo rescues germ-band retraction without producing dominant gain-of-function defects, suggesting that hindsight's role in germ-band retraction is permissive rather than instructive. Previous analyses have shown that hindsight is required for maintenance of the differentiated amnioserosa (Frank, L. C. and Rushlow, C. (1996) Development 122, 1343–1352). Two classes of models are consistent with the present data. First, hindsight's function in germ-band retraction may be limited to maintenance of the amnioserosa which then plays a physical role in the retraction process through contact with cells of the epidermal ectoderm. Second, hindsight might function both to maintain the amnioserosa and to regulate chemical signaling from the amnioserosa to the epidermal ectoderm, thus coordinating the cell shape changes and movements that drive germ-band retraction.

Isolation and characterization of a Drosophila gene essential for early embryonic development and formation of cortical cleavage furrows

We have isolated a new female sterile mutant from Drosophila melanogaster, which arrests the embryonic development during the transition from syncytial to cellular blastoderm. Cytological analysis of the mutant embryos indicates that pseudocleavage furrows in the syncytial blastoderm are abnormal but not completely disrupted. However, cleavage furrows during cellularization are totally disorganized, and no embryos can develop beyond this stage. Consistent with this observation, the expression of this gene peaks around the cellular blastoderm and not in any later developmental stages. Based on immunofluorescence experiments, the protein product of this gene is localized in both pseudocleavage furrows at the syncytial blastoderm and in the cleavage furrows during the cellularization stage. Sequence homology analysis demonstrates a modest, but statistically significant, similarity of this protein with the carboxyl-terminal domains of dystrophin and a family of proteins collectively known as apodystrophins. It is possible that this protein may play an essential role in organizing and maintaining a specialized cytoskeletal structure, a function also suggested for dystrophin and apodystrophins.

Pollux, a novel Drosophila adhesion molecule, belongs to a family of proteins expressed in plants, yeast, nematodes, and man

Adhesion molecules have pivotal roles in cellular processes critical to the development and maintenance of multicellular organisms. Here we describe a new member of the adhesive repertoire encoded by the Drosophila pollux (plx) gene. Marked by a novel 74-amino-acid domain, Plx belongs to a highly conserved family with members in plants, yeast, nematodes, and man, including the human oncoprotein TRE17. Essential for viability, plx mutant analysis indicates that larval death is attributable to asphyxiation brought on by fluid-congested tracheal tubes. Ultrastructural examination of mutant tracheae reveals defects in cell-extracellular matrix contacts. During embryogenesis, Plx uniformly covers the apical surface of cellular blastoderm cells. It is later found regionally concentrated along subsets of central nervous system axon pathways and on the apical surface of the trachea's tubular epithelium. Cell attachment assays demonstrate that Plx can serve as a ligand for cell surface integrins. Plx also contains a motor neuron-selective adhesive site, multiple proteoglycan-binding motifs, and a leucine zipper: all suggest possible associations with additional components of the adhesion complex.

Monoclonal antibody raised against murine IL-1 alpha peptide cross-reacts with a 60-kDa antigen in early Drosophila melanogaster embryo

Whole-mounts of Drosophila embryos were stained with the monoclonal antibody Vmp 18, raised against the peptide 199-208 of murine interleukin 1/ alpha. Immunofluorescence observations showed that the antibody cross-reacted with an antigenic determinant that changed in localization during Drosophila development. In syncytial Drosophila embryos, the antibody recognized an epitope localized on the nuclear envelope throughout mitotic division. As cellularization occurred, the fluorescence was mainly concentrated in the apical region of the blastoderm cells. Western blot analysis of whole Drosophila embryo extracts showed that the antibody recognized a 60-kDa protein in syncytial embryos and during germ band elongation. This suggests that the 60-kDa antigen undergoes dynamic redistribution during embryogenesis.

Differential synthesis and cytolocalization of prosomes in chick embryos during development

Prosomes, also called "multicatalytic proteinase" or proteasomes, were purified from chick embryos of different developmental stages by a simple, single-step procedure. These were characterized by their characteristic protein patterns determined by SDS polyacrylamide gel electrophoresis (SDS PAGE) and immunoblotting with four monoclonal antibodies, namely, anti-p27, -p28, -p29 and -p31, prepared against duck prosomes. In vitro labeling of embryos with 35S-methionine followed by SDS PAGE and fluorography of the purified prosomes revealed that their polypeptides are differentially synthesized at various stages during development. Among 12 polypeptides (p21 to p56), p21 is synthesized at the beginning of gastrulation (stage 2) followed by the synthesis of p24 at stage 3. Nine other polypeptides (p25 to p35) are synthesized at the head-fold stage (stage 6), while the synthesis of polypeptide p56 is only detected at stage 10 (10-somite stage). Indirect immunofluorescence studies, with the 4 monoclonal antibodies, demonstrated 3 distinct, developmental stage-specific patterns of cytodistribution of these four prosome polypeptides in the embryos. During early embryogenesis, these are uniformly nuclear in location, while at later stages (stage 4 onwards) they are also present in the cytoplasm. Interestingly, one of the antigens (p 28), although found uniformly in all types of tissues in the embryos up to the gastrulation stage, is undetectable in the neural tissues and nonuniformly distributed in other tissues of stage-10 embryos. These data suggest that there are subcomponents of prosomes which are synthesized as well as distributed in an independent manner during development, possibly reflecting subcomponent-specific multiple functions of these particles.

A new heparan sulfate proteoglycan in the extracellular matrix of the developing chick embryo

A new heparan sulfate proteoglycan was identified by two monoclonal antibodies. The antibodies (hybridoma clones 6C4 and 1B11) were generated from mice immunized with inner limiting membranes of the embryonic chick retina. The proteoglycan had an apparent molecular weight of 250 kDa with a core protein of 180 kDa. Antibodies to perlecan and to a recently identified brain-derived heparan sulfate proteoglycan did not cross-react with purified 6C4/1B11 antigen, confirming that the three proteoglycans are not related. The 6C4/1B11 proteoglycan was abundant in basal laminae, such as the inner limiting membrane of the retina, the lens capsule, the epidermal, the pial, and the muscle basal laminae, and the vitreous body. The distribution and developmental expression of the 6C4/1B11 proteoglycan was different than that of perlecan and the brain-derived heparan sulfate proteoglycan. When used as a substrate for embryonic retinal explants, the proteoglycan did not support axonal outgrowth in vitro. The data present a new heparan sulfate proteoglycan and demonstrate the existence of at least three different heparan sulfate proteoglycans in the developing chick embryo with partially overlapping distribution.

Localized expression of a novel micropia-like element in the blastoderm of Drosophila melanogaster is dependent on the anterior morphogen bicoid

We have identified a novel transposon-like element of Drosophila melanogaster that is present in approximately 20 copies in the genome. It codes for a polyprotein containing the diagnostic sequence motifs for a nucleic acid binding CCHC protein, a proteinase, a reverse transcriptase and an integrase as typically found in retroviruses. Owing to its early expression in the blastoderm embryo, and its close relationship to micropia, a previously identified Drosophila retrotransposon, we termed the novel element "blastopia". The spatially restricted expression of blastopia transcripts in head anlagen of the blastoderm embryo is under the direct or indirect control of the Drosophila morphogen bicoid, which is normally required to establish the anterior pattern elements in the embryo. Our results suggest that a blastopia element acts as an "enhancer trap", and thereby participates in the control of an as yet unidentified gene normally expressed in the head anlagen of the embryo.

Presence of mitochondrial large ribosomal RNA outside mitochondria in germ plasm of Drosophila melanogaster

Mitochondrial large ribosomal RNA (mtlrRNA) has been identified as a cytoplasmic factor that induces pole cell formation in embryos whose ability to form a germ line has been abolished by treatment with ultraviolet light. In situ hybridization analyses reveal that mtlrRNA is enriched in germ plasm and is tightly associated with polar granules, the distinctive organelles of germ plasm, which supports the idea that mtlrRNA functions in pole cell formation. This suggests that a product from the mitochondrial genome, along with nuclear products, participates in a key event in embryonic development: determination of the germ line.

Distribution of a nuclear envelope antigen during the syncytial mitoses of the early Drosophila embryo as revealed by laser scanning confocal microscopy

The changing distribution of a nuclear envelope antigen recognized by a monoclonal antibody raised against human fibroblast vimentin during the syncytial mitoses of the Drosophila embryo has been studied with a confocal laser scanning microscope. The antigen appears very early as irregular aggregates in the peripheral cytoplasm of the preblastoderm embryo. As the first nuclei reach the periplasm the antigen is localized on the nuclear envelope and the cytoplasmic staining decreases. In addition to the perinuclear labeling we observed intense midzone and polar staining during the mitotic cycle. A possible relationship between polar localization of the antigen and centrosome position is discussed.

Spatial distribution of the Sm antigen in Drosophila early embryos

Anti-Sm antibodies recognize the major small nuclear RNA-protein particles (snRNPs) involved in pre-mRNA processing. The spatial distribution of the snRNPs has been investigated in Drosophila embryos up to the cellularization stage (cycle 14), using the Y12 anti-Sm antibody. Our results show that: 1) all or most of the Sm antigen is localized in the cytoplasm of the syncytial blastoderm until the 12th cycle of division, in both the nuclear and cytoplasmic compartments at cycle 13, and then in the nuclei at cycle 14 and later. This relocalization takes place when zygotic transcriptional activation occurs; 2) at the subcellular level, the Sm antigen localizes in a speckled pattern and in foci-like structures within the nucleus of Drosophila blastoderm embryos; 3) strikingly, some nuclei of embryos at the 14th cycle appear to contain more snRNPs than others. The position of these nuclei differs from one embryo to another, and their distribution does not resemble any known developmental pattern of Drosophila embryogenesis. We propose that random differences in snRNP concentration may serve as an epigenetic signal for stochastic events occurring during development.

Restricted spatial and temporal expression of G-protein alpha subunits during Drosophila embryogenesis

Of the known signal transduction mechanisms, the most evolutionarily ancient is mediated by a family of heterotrimeric guanine nucleotide binding proteins or G proteins. In simple organisms, this form of sensory transduction is used exclusively to convey signals of developmental consequence. In metazoan organisms, however, the developmental role of G-protein-coupled sensory transduction has been more difficult to elucidate because of the wide variety of signals (peptides, small molecules, odorants, hormones, etc.) that use this form of sensory transduction. We have begun to examine the role of G-protein-coupled signaling during development by investigating the expression during Drosophila embryogenesis of a limited set of G proteins. Since these proteins are a common component of all G-protein-coupled signaling systems, their developmental pattern of expression should indicate when and where programmed changes in gene activity are initiated by, or involve the participation of, G-protein-coupled signaling events. We have focused on the spatial and temporal expression pattern of three different Drosophila G-protein alpha subunits by northern blot analysis, in situ hybridization and immunocytochemistry using antibodies directed to peptides specifically found in each alpha subunit. From the spatial and temporal restriction of the expression of each protein, our results suggest that different forms of G-protein-coupled sensory transduction may mediate developmental interactions during both early and late stages of embryogenesis and may participate in a variety of specific developmental processes such as the establishment of embryonic position, the ontogeny of the nervous system and organogenesis.

The origin of reactive oxygen species in mouse embryos cultured in vitro

The increase in production of reactive oxygen species such as H2O2 at the G2/M phase of the second cell cycle may be related to the in vitro block to development of mouse 2-cell embryos. The occurrence of the H2O2 rise is independent of the activation of the embryonic genome and of passage through the S, G2 and M phases of the first cell cycle and G1 and M phases of the second cell cycle, but does require the activation of the unfertilized oocyte. The H2O2 is produced via dismutation of superoxide by the enzyme superoxide dismutase. Production of superoxide via mitochondrial, NADPH-oxidase and xanthine/xanthine oxidase systems has been investigated. The evidence suggests that superoxide, and thereby H2O2, is produced by the xanthine/xanthine oxidase system, but an involvement of the other superoxide generating systems has not been excluded. The relation between H2O2 and development in vitro is discussed.

Features of polyingression and primitive streak ingression through the basal lamina in the chicken blastoderm

The de-epithelialization of cells of the upper layer during the phenomena of polyingression and primitive streak ingression was studied by analyzing, from the time of laying to the end of gastrulation, the ultrastructure of the basal lamina underlying the upper layer. The electron density of the basal lamina and associated extracellular materials was enhanced by addition of tannic acid to the fixative. Special attention was also paid to the spatial and temporal distribution of blebs at the basal surface of the upper layer, and to the contribution of the de-epithelialized cells to the formation of the deep layer. The results indicate that a nascent basal lamina is already present at the time of laying, especially beneath regions of the area pellucida where polyingression is not apparent. From the onset of incubation, the basal lamina rapidly develops, and it is interrupted by a large number of blebs. However, during the first 6-8 h of incubation, i.e., stages 1-2 of Vakaet (Arch. Biol. (Liège) 81:387-426, 1970), a downward movement of de-epithelialized cells that insert into the deep layer and form the endophyll persists cranially. This phenomenon of polyingression, which starts during the intrauterine period, probably extends from caudal to cranial and comes to an end by stage 3. During these first three stages, the number of blebs progressively decreases, especially in the cranial part of the area pellucida, and a thicker, continuous basal lamina associated with numerous interstitial bodies is laid down. The caudal part of the upper layer is still actively blebbing at that time. Due to the convergence of this area toward the axis of the blastoderm, which leads to ingression at and elongation of the primitive streak up to and including stage 6, the number of blebs at the basal surface of the upper layer progressively decreases. From stage 7 on, blebs are virtually absent; shortening of the primitive streak and formation of the head process begin. At the level of the head process, primitive streak ingression has ceased and a novel basal lamina is progressively deposited beneath the upper layer. By stage 9, a thick, smooth basal lamina physically separates the upper layer from the head mesenchyme. Summarizing, at the time of gastrulation, the presence of blebs that perforate the basal lamina is correlated with the de-epithelialization of cells. Before incubation, however, de-epithelialization of upper-layer cells occurs before the assembly of the basal lamina.(ABSTRACT TRUNCATED AT 400 WORDS)

Dynamic changes in the distribution of cytoplasmic myosin during Drosophila embryogenesis

Dramatic changes in the localization of conventional non-muscle myosin characterize early embryogenesis in Drosophila melanogaster. During cellularization, myosin is concentrated around the furrow canals that form the leading margin of the plasma membrane as it plunges inward to package each somatic nucleus into a columnar epithelial cell. During gastrulation, there is specific anti-myosin staining at the apical ends of those cells that change shape in regions of invagination. Both of these localizations appear to result from a redistribution of a cortical store of maternal myosin. In the preblastoderm embryo, myosin is localized to the egg cortex, sub-cortical arrays of inclusions, and, diffusely, the yolk-free periplasm. At the syncytial blastoderm stage, myosin is found within cytoskeletal caps associated with the somatic nuclei at the embryonic surface. Following the final syncytial division, these myosin caps give rise to the myosin rings observed during cellularization. These distributions are observed with both whole immune serum and affinity-purified antibodies directed against Drosophila non-muscle myosin heavy chain. They are not detected in embryos stained with anti-Drosophila muscle myosin antiserum or with preimmune serum. Although immunolocalization can only suggest possible function, these myosin localizations and the coincident changes in cell morphology are consistent with a key role for non-muscle myosin in powering cellularization and gastrulation during embryogenesis.

The Drosophila segmentation gene runt encodes a novel nuclear regulatory protein that is also expressed in the developing nervous system

Generation of the anterior-posterior body pattern in the Drosophila embryo requires the activity of the segmentation genes. The segmentation gene runt has been classified as one of the primary pair-rule genes because of the pivotal role it plays in regulating the expression of other pair-rule genes. Here, we present the structure of this gene and describe the pattern of runt protein expression during embryogenesis. The deduced protein sequence shows no obvious overall homology with any sequences in the data base. The absence of an identifiable transcription factor motif (e.g., homeo box, zinc finger, leucine zipper, or helix-loop-helix) makes runt different from the other early-acting segmentation proteins. A runt-specific polyclonal antibody was generated and used to demonstrate that the subcellular location of the protein is in the nucleus. Double-staining immunolocalization experiments were used to determine the overlap of the runt protein pattern with the patterns of the pair-rule genes hairy (h), even-skipped (eve), and fushi tarazu (ftz). We found that the patterns of runt and hairy are complementary. Their phasing is shifted anteriorly by two cell diameters with respect to the complementary eve and ftz patterns. Experiments with the runt antibody also indicated that the protein is present throughout embryogenesis and is expressed extensively in the developing central and peripheral nervous system.