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PubMed2000

Characterization of sea urchin unconventional myosins and analysis of their patterns of expression during early embryogenesis.

Early sea urchin development requires a dynamic reorganization of both the actin cytoskeleton and cytoskeletal interactions with cellular membranes. These events may involve the activities of multiple members of the superfamily of myosin motor proteins. Using RT-PCR with degenerate myosin primers, we identified 11 myosin mRNAs expressed in unfertilized eggs and coelomocytes of the sea urchin Strongylocentrotus purpuratus. Seven of these sea urchin myosins belonged to myosin classes Igamma, II, V, VI, VII, IX, and amoeboid-type I, and the remaining four may be from novel classes. Sea urchin myosins-V, -VI, -VII, and amoeboid-type-I were either completely or partially cloned and their molecular structures characterized. Sea urchin myosins-V, -VI, -VII, and amoeboid-type-I shared a high degree of sequence identity with their respective family members from vertebrates and they retained their class-specific structure and domain organization. Analysis of expression of myosin-V, -VI, -VII, and amoeboid-type-I mRNAs during development revealed that each myosin mRNA displayed a distinct temporal pattern of expression, suggesting that myosins might be involved in specific events of early embryogenesis. Interestingly, the onset of gastrulation appeared to be a pivotal point in modulation of myosin mRNA expression. The presence of multiple myosin mRNAs in eggs and embryos provides insight into the potential involvement of multiple specific motor proteins in the actin-dependent events of embryo development.

Amino Acid Sequence↗

PubMed2001

Syntaxin, VAMP, and Rab3 are selectively expressed during sea urchin embryogenesis.

SNARE and rab protein family members were originally identified in terminally differentiated cell types. These proteins are phylogenetically conserved and while compelling evidence demonstrates their involvement in the secretory pathway, their exact function is debated. We recently identified SNARE protein family members in the sea urchin egg and provided evidence that rab3 functions in the exocytosis of cortical granules. Here we tested the hypothesis that these same proteins might also be present throughout embryogenesis to mediate membrane fusion events. We provide evidence that the sea urchin possesses a low complexity of gene family members of syntaxin, VAMP, and rab3 and that these proteins are not only present during development, but are enriched in regions of the embryo with active secretory roles. We found accumulation of each family member in the apical and basal aspects of cleaving blastomeres, indicative of bidirectional secretion into the extraembryonic environment and blastocoel. Elevated levels of syntaxin, VAMP, and rab3 were also found in the mesodermally derived pigment cells that invade and move within the ectoderm. These cells likely rely on SNARE and rab proteins to enable mobility by mediating the secretion of enzymes that break adhesion to neighboring cells and the extracellular matrix. In addition, these secretory proteins are enriched in the gut following gastrulation. Thus, we conclude that VAMP, syntaxin, and rab3 mediate a variety of secretory events that is important for development.

Animals↗

PubMed1988

Adhesion mechanisms in embryogenesis and in cancer invasion and metastasis.

Cell-substratum and cell-cell adhesion mechanisms contribute to the development of animal form. The adhesive status of embryonic cells has been analysed during epithelial-mesenchymal cell interconversion and in cell migrations. Clear-cut examples of the modulation of cell adhesion molecules (CAMs) have been described at critical periods of morphogenesis. In chick embryos the three primary CAMs (N-CAM. L-CAM and N-cadherin) present early in embryogenesis are expressed later in a defined pattern during morphogenesis and histogenesis. The axial mesoderm derived from gastrulating cells expresses increasing amounts of N-cadherin and N-CAM. During metamerization these two adhesion molecules become abundant at somitic cell surfaces. Both CAMs are functional in an in vitro aggregation assay; however, the calcium-dependent adhesion molecule N-cadherin is more sensitive to perturbation by specific antibodies. Neural crest cells which separate from the neural epithelium lose their primary CAMs in a defined time-sequence. Adhesion to fibronectins via specific surface receptors becomes a predominant interaction during the migratory process, while some primary and secondary CAMs are expressed de novo during the ontogeny of the peripheral nervous system. In vitro, different fibronectin functional domains have been identified in the attachment, spreading and migration of neural crest cells. The fibronectin receptors which transduce the adhesive signals play a key role in the control of cell movement. All these results have prompted us to examine whether similar mechanisms operate in carcinoma cell invasion and metastasis. In vitro, rat bladder transitional carcinoma cells convert reversibly into invasive mesenchymal cells. A rapid modulation of adhesive properties is found during the epithelial-mesenchymal carcinoma cell interconversion. The different model systems analysed demonstrate that a limited repertoire of adhesion molecules, expressed in a well-defined spatiotemporal pattern, is involved in tissue formation and in key processes of tumour spread.

Animals↗

PubMed1993

Expression of the dystrophin-related protein (utrophin) gene during mouse embryogenesis.

The utrophin (UTRN) locus is the autosomal homologue of the DMD (Duchenne muscular dystrophy) gene and encodes a protein, utrophin which is thought to be upregulated in the absence of dystrophin. In this study the spatial and temporal expression of the UTRN gene has been examined during mouse embryogenesis and compared with that of the DMD gene. The patterns of expression of these two genes are very different. Whilst DMD is expressed largely in mesodermal derivatives such as cardiac and striated muscle, UTRN shows a more widespread distribution and is expressed in neural tube, tissues which originate from neural crest and a variety of other sites of non-neural origin. In early embryos UTRN transcripts initially accumulate in the mid-neural plate and thereafter in the caudal neural tube. UTRN mRNA then becomes abundant in a subset of neural crest cell derived tissues, in particular the spinal and facial ganglia and ossifying facial cartilages. UTRN is also expressed in a variety of other sites and organs such as the tendon primordia in the digits, the pituitary, thyroid and adrenal glands, cardiac muscle, kidney and lung, follicles of the vibrissae and the outflow tract of the heart. Several patterns of UTRN expression are apparent and we discuss the possibility that these can be ascribed to a family of mRNAs transcribed from the UTRN gene using alternative promoters.

Animals↗

PubMed1988

Horseshoe kidney: a new theory on its embryogenesis based on the study of a 16-mm human embryo.

We studied a human embryo of 16 mm crown-rump (CR) length in excellent condition with a horseshoe kidney malformation. An exhaustive study of this specimen and a review of published material on the human embryo brings us to propose a new theory on the embryogenesis of this malformation. The most commonly accepted theory consists of a mechanical interpretation based on the relation between the metanephroi and the umbilical arteries during the development of the latter. Nevertheless, in those cases where renal parenchyma constitutes the isthmic region, we believe that these arise from nephrogenic cells that have migrated across the primitive streak in the final phase of gastrulation and thus arise from the posterior nephrogenic area of the epiblast.

Embryonic and Fetal Development↗

PubMed2003

Dynamic expression of Krüppel-like factor 4 (Klf4), a target of transcription factor AP-2alpha during murine mid-embryogenesis.

Krüppel-like factor 4 (Klf4) belongs to the family of transcription factors that are thought to be involved in the regulation of epithelial and germ cell differentiation, based on their expression in postproliferative cells of the skin, gut, and testes. Gene ablation experiments suggest that Klf4 plays a role in keratinocyte differentiation, since mice lacking Klf4 fail to establish proper barrier function and, as a consequence, die postnatally due to dehydration. Recent studies have shown that Klf4 is also expressed in postnatal male mice, in postmeiotic sperm cells undergoing terminal differentiation into sperm cells. However, prior to the current study, the expression pattern of Klf4 during early and mid-embryogenesis had not been examined. Here we demonstrate that Klf4 transcripts can be detected from embryonic day 4.5 (E4.5) on in the developing conceptus, and that Klf4 expression before E10 is restricted to extraembryonic tissues. The embryo proper displays a highly dynamic and changing Klf4 signal from E10 of murine development on. In addition to being expressed in a stripe of mesenchymal cells extending from the forelimb bud rostrally over the branchial arches to the developing eye, Klf4 is also expressed in the mesenchyme surrounding the nasal pit at day E11.5. In addition, Klf4 has been detected in the apical ectodermal ridge and adjacent mesenchymal cells in the limb buds, and in mesenchymal cells of the developing body wall in trunk areas. These findings suggest that Klf4 plays an important role in regulating cellular proliferation, which underlies the morphogenetic changes that shape the developing embryo.

Animals↗

PubMed2006

Evidence that some events of mammalian embryogenesis can result from differential growth, making migration unnecessary.

Three events during mammalian embryogenesis were reexamined that traditionally have been considered to be migratory. Using reconstructions of serially sectioned rat and human embryos and computer imaging, this descriptive study reexamined the following: sclerotome formation from the somite, spinal ganglion formation from the neural crest, and thyroid, parathyroid, and thymus gland formations from pharyngeal endoderm. The aim was to determine if the positional changes of the developing structures could be explained by differential growth (i.e., changes in the size and shape of the embryo and its parts) rather than migration (i.e., structures moving from one region of the embryo to another). Embryos and many of their internal structures, especially the neural tube, rapidly change in size and shape during the period when migration is described, but these phenomena were not considered in past studies. Surface reference points were used in past investigations that also move as the embryo and its internal structures enlarge. Computer imaging makes it feasible for the first time to keep magnifications identical for each series of reconstructions, rendering each one equivalent to one frame of a motion picture film. Using this technique together with more centralized, less mobile reference points, the study concludes that the positional changes that occur during the three events can be explained by differential growth. Anat Rec (Part B: New Anat) 289B:53-63, 2006. (c) 2006 Wiley-Liss, Inc.

Animals↗

PubMed2004

Matrix loading: assembly of extracellular matrix collagen fibrils during embryogenesis.

Nothing in biology stimulates the imagination like the development of a single fertilized egg into a newborn child. Consequently, a major focus of biomedical research is aimed at understanding cell differentiation, proliferation, and specialization during child health and human development. However, the fact that the increase in size and shape of the growing embryo has as much to do with the extracellular matrix (ECM) as with the cells themselves, is largely overlooked. Cells in developing tissues are surrounded by a fiber-composite ECM that transmits mechanical stimuli, maintains the shape of developing tissues, and functions as a scaffold for cell migration and attachment. The major structural element of the ECM is the collagen fibril. The fibrils, which are indeterminate in length, are arranged in different tissues in exquisite supramolecular architectures, including parallel bundles, orthogonal lamellae, and concentric weaves. This article reviews our current understanding of the synthesis and assembly of collagen fibrils, and discusses challenging questions about how cells assemble an organized ECM during embryogenesis.

Actins↗

PubMed2001

Three sons of fortune: early embryogenesis, evolution and ecology of nematodes.

Comparative analysis of nematode development has revealed considerable variations in how the fates of embryonic cells are specified. Such early variations seem enigmatic as they do not influence the resultant structure or performance of the emerging animal. Three different nematode species are used to consider why alternative ways to reach the same goal may have been established during evolution and why early steps of embryogenesis are particularly variable. A scenario is sketched with a shift from late to early cell specification, along with an increase in maternal contribution and developmental tempo and a decrease in regulative potential expressing different developmental strategies. Future studies of larger numbers of species are needed to assess the extent of such variations and to understand more fully the underlying mechanisms, rules and driving forces.

Animals↗

PubMed1990

The expression and posttranslational modification of a neuron-specific beta-tubulin isotype during chick embryogenesis.

Five beta-tubulin isotypes are expressed differentially during chicken brain development. One of these isotypes is encoded by the gene c beta 4 and has been assigned to an isotypic family designated as Class III (beta III). In the nervous system of higher vertebrates, beta III is synthesized exclusively by neurons. A beta III-specific monoclonal antibody was used to determine when during chick embryogenesis c beta 4 is expressed, the cellular localization of beta III, and the number of charge variants (isoforms) into which beta III can be resolved by isoelectric focusing. On Western blots, beta III is first detectable at stages 12-13. Thereafter, the relative abundance of beta III in brain increases steadily, apparently in conjunction with the rate of neural differentiation. The isotype was not detectable in non-neural tissue extracts from older embryos (days 10-14) and hatchlings. Western blots of protein separated by two-dimensional gel electrophoresis (2D-PAGE) reveal that the number of beta III isoforms increases from one to three during neural development. This evidence indicates that beta III is a substrate for developmentally regulated, multiple-site posttranslational modification. Immunocytochemical studies reveal that while c beta 4 expression is restricted predominantly to the nervous system, it is transiently expressed in some embryonic structures. More importantly, in the nervous system, immunoreactive cells were located primarily in the non-proliferative marginal zone of the neural epithelia. Regions containing primarily mitotic neuroblasts were virtually unstained. This localization pattern indicates that c beta 4 expression occurs either during or immediately following terminal mitosis, and suggests that beta III may have a unique role during early neuronal differentiation and neurite outgrowth.

Animals↗

PubMed1977

Experimental analysis of embryogenesis of cerebellum in rat. II. Morphogenetic malformations following x-ray irradiation on day 18 of gestation.

Rat embryos of 18 days gestation were exposed in utero to 170 R of X-ray irradiation. Embryos were collected six hours, 1, 2, and 3 days after irradiation, and animals of 2-, 6-, 15- and 30-day-old postnatal age were sacrificed. Six hours after irradiation pyknosis of cells was notices in the external granular layer along the posterior aspect of the cerebellum. Neuroblasts, destined to differentiate into Purkinje cells, were found arrested in their migratory path. During subsequent periods of embryogenesis the external granular layer was found recovered, and clustering of the neuroblasts were disorganized and fragmented. This abnormal clustering of neuroblasts was permanent, and the external granular layer followed the same abnormal pattern in its growth. During postnatal development the internal granular layer also was found to follow the abnormal pattern of Purkinje cell layer. These abnormal developmental events were seen to lead to malformed folia in the anterior regions of the cerebellum. In addition to it the cerebellum of X-ray irradiated animals appeared smaller than the normal. Issues having a bearing on the differential radiosensitivity of different cells, factors determining the small size of the cerebellum, and cellular events determining the morphogenetic malformations are discussed.

Animals↗

PubMed1979

Axonal guidance during embryogenesis and regeneration in the spinal cord of the newt: the blueprint hypothesis of neuronal pathway patterning.

In our previous studies on studies on spinal cord regeneration in the adult lizard and the newt, we observed that the radial processes of the regenerating ependyma form between them channels which are subsequently invaded by growing neurites. In the present study we compare embryogenesis of the newt spinal cord with regeneration in the adult. Except for minor differences, we observed that the germinal neuroepithelium of the embryo and larva patterns the longitudinal neural tracts in a similar manner. With these facts in mind we propose the blueprint hypothesis which asserts that inherent in the primitive germinal neuroepithelium and its derivative primitive glia is the pattern of the primary neuronal pathways which is expressed in neurogenesis as formed channels or spaces between the processes of the epithelial cells, the surfaces of which contain trace pathways which the growing neurites follow toward their destination. The trace pathways are envisoned as mechanical-chemical itineraries which the neurities follow according to their individual affinities. The hypothesis is compared to extant theories and the limitations in central nervous regeneration of vertebrates is compared.

Animals↗

PubMed1993

Immunocytochemical analysis of a novel carbohydrate differentiation antigen (CDA-3C2) associated with olfactory and otic systems during embryogenesis in the rat.

Carbohydrate differentiation antigens are known to display specific patterns of expression during mammalian development and are thought to participate in significant morphogenetic events. In the present study, two monoclonal antibodies that react with a novel carbohydrate differentiation antigen (CDA-3C2) were used to analyze, by light microscopy, the spatiotemporal distribution of this unique high molecular weight antigen during embryogenesis in the rat. Correlative analysis of the development of peripheral neural structures, in which CDA-3C2 was expressed, was carried out with an anti-neurofilament antibody. Enzymatic digestion, combined with Western blots, reveal that the CDA-3C2 epitope is a carbohydrate which is carried on a high molecular weight glycoprotein with a mass of greater than 1 million Daltons. Characteristic of carbohydrate antigens, immunoreactivity was found in several distinct cellular patterns: only along the apical border of cells, along lateral and basal membranes of cells, and extracellular-like staining in the mesenchyme. During neurulation, CDA-3C2 showed differential staining in the ectoderm, distinguishing lateral from neural regions. Following closure of the neural tube, there was a striking specificity of expression of CDA-3C2 in the periphery, found almost exclusively in olfactory and otic epithelial structures. While CDA-3C2 is found in placode-derived tissues that subserve sensory transduction, it appears to be primarily associated with the supportive cells (and their secretions) in both otic and olfactory regions and less so with the sensory cells. The data suggest that a unique carbohydrate antigen on a large macromolecule may play a role in neurulation and/or morphogenesis of the placode-derived otic and olfactory structures.

Animals↗

PubMed2002

Survivin mRNA is down-regulated during early Xenopus laevis embryogenesis.

One of the hallmarks of early development is the rapid proliferation of cells immediately after fertilization. Many of the rules that govern cell division in normal somatic cells, such as contact inhibition and apoptosis, seem temporarily suspended in the early embryo. A similar suspension of mechanisms normally regulating cell division occurs in the development of cancer. Survivin, an inhibitor of apoptosis and a positive regulator of progression through the cell cycle, localizes to the mitotic spindle and interacts with several proapoptotic caspases. Survivin protein expression has been studied during the development of the salivary gland in mouse. However, the regulation of survivin during the critical transitions defining oocyte maturation and the early restriction of developmental potential are not easily examined in the mouse. We therefore studied survivin mRNA expression during oogenesis and early embryogenesis in Xenopus laevis. We found that survivin mRNA is present in the earliest stages of Xenopus oocytes and that it accumulates during oogenesis. Progesterone-induced maturation of Xenopus oocytes leads to polyadenylation of the survivin transcript. Survivin mRNA is also present in early Xenopus embryos. After the onset of zygotic transcription, however, the amount of survivin mRNA declines rapidly to undetectable levels. This decrease in survivin mRNA correlates temporally with both the slowing of the cell cycle and the onset of endogenous embryonic apoptosis. With the exception of the ovary, survivin mRNA was undetectable in all adult Xenopus tissues examined.

Amino Acid Sequence↗

PubMed2003

RhoA is highly up-regulated in the process of early heart development of the chick and important for normal embryogenesis.

We have used molecular techniques, combined with classic embryological methods, to identify up-regulated genes associated with early heart development. One of the cDNAs identified and isolated by screening a chick lambda cDNA library was the small guanosine triphosphatase RhoA. RhoA has at least three different length mRNA species, each varying in the length of the 3' untranslated region. In situ hybridisation and immunocytochemistry analysis of RhoA expression show marked up-regulation in the heart-forming region. In other systems, RhoA signalling has been shown to be important for both gene expression and morphology. To investigate the function of RhoA in early heart development, we used small interfering RNAs (siRNA) in early chick embryos. Disruption of RhoA expression by siRNA treatment resulted in lack of heart tube fusion and abnormal head development. These data indicate that RhoA is important for normal embryogenesis.

3' Untranslated Regions↗

PubMed2003

Differential expression of the two Drosophila fos/kayak transcripts during oogenesis and embryogenesis.

The Dfos/kayak gene encodes a bZIP protein, DFos, required in a large variety of differentiation and morphogenetic processes throughout Drosophila development. The recent availability of an expressed sequence tag (EST) sequence led us to identify a novel kay mRNA encoding a deduced DFos isoform showing a specific NH(2)-terminal region. To gain further insight into the function and the regulation of this gene, we have investigated the expression pattern of the two kay mRNA isoforms, kay-RA and kay-RB, during oogenesis and embryogenesis by whole-mount in situ hybridization. Results show that, although the two kay RNA isoforms display fully distinct patterns of transcription during oogenesis, they show partially overlapping expression profiles in embryos. These data reveal a previously unsuspected level of complexity in the regulation of the expression of the kay gene. In addition, they suggest a possible requirement for this gene in the invagination processes during early gastrula stages.

Amino Acid Sequence↗

PubMed2003

Skin-specific expression of ictacalcin, a homolog of the S100 genes, during zebrafish embryogenesis.

Full-length cDNA coding for the ictacalcin gene, a homolog of the S100 genes, was isolated in zebrafish and mapped on linkage group 16 using the LN54 radiation hybrid panel. The homology and phylogenetic analyses, based on the deduced amino acid sequences, showed the orthologous relationship of ictacalcin genes between zebrafish and other fish species. However, ictacalcin genes constitute an out-group with respect to other members of the S100 gene family. This result supports the findings that fish ictacalcin genes are new members of the S100 gene family and may have evolved after the divergence of teleosts and tetrapods. The zebrafish ictacalcin gene was zygotically transcribed from 12 hours postfertilization onward and was stably expressed throughout adulthood. During zebrafish embryogenesis, the ictacalcin gene was specifically expressed in striated epidermal cells covering the entire embryo. The ictacalcin staining in keratinocytes of striated epithelia was absent in the cytoplasm surrounding the nuclei, but it was highly concentrated in the peripheral margin. Tissues enriched with epithelia folds, such as olfactory epithelium, hatching gland, pectoral fin buds, urogenital opening, and pharynx, showed a robust ictacalcin expression. The strikingly heavy staining of ictacalcin in the pharyngeal region provides us with an early marker to follow the pharynx formation in zebrafish embryos.

Amino Acid Sequence↗

PubMed2004

T-box genes in early embryogenesis.

The T-box gene family, encoding related DNA-binding transcriptional regulators, plays an essential role in controlling many aspects of embryogenesis in a wide variety of organisms. The T-box genes exhibit diverse patterns of spatial and temporal expression in the developing embryo, and both genetic and molecular embryological studies have demonstrated their importance in regulating cell fate decisions that establish the early body plan, and in later processes underlying organogenesis. Despite these studies, little is known of either the regulation of the T-box genes or the identities of their transcriptional targets. The aim of this review is to examine the diverse yet conserved roles of several T-box genes in regulating early patterning in chordates and to discuss possible mechanisms through which this functional diversity might arise. Developmental Dynamics 229:201-218, 2004.

Amino Acid Sequence↗