Correlation between IL-6 and invasiveness of ectoderm cells of embryo in early pregnancy

This study aimed to explore the correlation between Interleukin-6 (IL-6) and invasiveness of ectoderm cells of embryo in early pregnancy, in order to further discuss whether IL-6 can enhance invasiveness of ectoderm cells. The study lays the foundation for determination of pathogenesis of some gestation period-related diseases. Differences in mRNA and protein expression of trophoblastic cell line JEG-3 cells in IL-6, matrix metalloproteinase-2 (MMP-2) and MMP-9 were analyzed; the regulating effect of different concentrations of IL-6 on invasive ability of trophoblast cells was studied by Transwell assay; the effect of IL-6 on proliferation of ectodermal cell line JEG-3 of embryo was analyzed by methyl thiazolyl tetrazolium (MTT) assay. The invasive number of JEG-3 cells incubated by IL-6 (10 ng/ml) was higher than that of the control group, and the difference had statistical significance (p < 0.05). Results of using MMT assay to detect the effect of IL-6 on proliferation of trophoblastic cell line JEG-3 showed that JEG-3 cells before and after processing had no significant difference from the control group (p >0.05). Therefore, IL-6 can enhance invasiveness of ectoderm cells of embryo through activation of MMP-2.

Differential expression of GSK3β and pS9GSK3β in normal human tissues: can pS9GSK3β be an epithelial marker?

Glycogen synthase kinase 3β (GSK3β) and phosphorylated GSK3β at Ser9 (pS9GSK3β) are crucial in cellular proliferation and metabolism. GSK3β and pS9GSK3β are deregulated in many diseases including tumors. Data on altered expression of GSK3β and pS9GSK3β are mainly limited to tumor tissues, thus the expression of GSK3β and pS9GSK3β in normal human tissue has been largely unknown. Thus, we examined the immunohistochemical localization of GSK3β and pS9GSK3β in human fetal and adult tissues, and also compared the expression pattern of GSK3β and pS9GSK3β with that of the CK7 and CK20. We found GSK3β expression in neurons of brain, myenteric plexus in gastrointestinal tract, squamous epithelium of skin, and mammary gland. The expression of pS9GSK3β was restricted to the epithelial cells of breast and pancreaticobiliary duct, distal nephron of kidney, gastrointestinal tract, fallopian tube, epididymis, secretory cell of prostatic gland, and umbrella cell of urinary tract. The staining pattern of pS9GSK3β and CK7 was overlapped in most organs except for gastrointestinal tract where CK7 was negative and CK20 was positive. Our results show that the expression of GSK3β may be associated with differentiation of ectodermal derived tissues and pS9GSK3β with that of epithelial cells of endodermal derived tissues in human. In addition, the expression of pS9GSK3β in the selective epithelial cells may indicate its association with secretory or barrier function of specific cells and may serve as another immunohistochemical marker for epithelial cells.

A key role for poly(ADP-ribose) polymerase 3 in ectodermal specification and neural crest development

Background

The PARP family member poly(ADP-ribose) polymerase 3 (PARP3) is structurally related to the well characterized PARP1 that orchestrates cellular responses to DNA strand breaks and cell death by the synthesis of poly(ADP-ribose). In contrast to PARP1 and PARP2, the functions of PARP3 are undefined. Here, we reveal critical functions for PARP3 during vertebrate development.

Principal Findings

We have used several in vitro and in vivo approaches to examine the possible functions of PARP3 as a transcriptional regulator, a function suggested from its previously reported association with several Polycomb group (PcG) proteins. We demonstrate that PARP3 gene occupancy in the human neuroblastoma cell line SK-N-SH occurs preferentially with developmental genes regulating cell fate specification, tissue patterning, craniofacial development and neurogenesis. Addressing the significance of this association during zebrafish development, we show that morpholino oligonucleotide-directed inhibition of parp3 expression in zebrafish impairs the expression of the neural crest cell specifier sox9a and of dlx3b/dlx4b, the formation of cranial sensory placodes, inner ears and pectoral fins. It delays pigmentation and severely impedes the development of the median fin fold and tail bud.

Conclusion

Our findings demonstrate that Parp3 is crucial in the early stages of zebrafish development, possibly by exerting its transcriptional regulatory functions as early as during the specification of the neural plate border.

PAR1 specifies ciliated cells in vertebrate ectoderm downstream of aPKC

Partitioning-defective 1 (PAR1) and atypical protein kinase C (aPKC) are conserved serine/threonine protein kinases implicated in the establishment of cell polarity in many species from yeast to humans. Here we investigate the roles of these protein kinases in cell fate determination in Xenopus epidermis. Early asymmetric cell divisions at blastula and gastrula stages give rise to the superficial (apical) and the deep (basal) cell layers of epidermal ectoderm. These two layers consist of cells with different intrinsic developmental potential, including superficial epidermal cells and deep ciliated cells. Our gain- and loss-of-function studies demonstrate that aPKC inhibits ciliated cell differentiation in Xenopus ectoderm and promotes superficial cell fates. We find that the crucial molecular substrate for aPKC is PAR1, which is localized in a complementary domain in superficial ectoderm cells. We show that PAR1 acts downstream of aPKC and is sufficient to stimulate ciliated cell differentiation and inhibit superficial epidermal cell fates. Our results suggest that aPKC and PAR1 function sequentially in a conserved molecular pathway that links apical-basal cell polarity to Notch signaling and cell fate determination. The observed patterning mechanism may operate in a wide range of epithelial tissues in many species.

Essential role of heparan sulfate 2-O-sulfotransferase in chick limb bud patterning and development

The interactions of heparan sulfate (HS) with heparin-binding growth factors, such as fibroblast growth factors (FGFs), depend greatly on the chain structures. O-Sulfations at various positions on the chain are major factors determining HS structure; therefore, O-sulfation patterns may play a crucial role in controlling the developmental and morphogenetic processes of various tissues and organs by spatiotemporally regulating the activities of heparin-binding growth factors. In a previous study, we found that HS-2-O-sulfotransferase is strongly expressed throughout the mesoderm of chick limb buds during the early stages of development. Here we show that inhibition of HS-2-O-sulfotransferase in the prospective limb region by small inhibitory RNA resulted in the truncation of limb buds and reduced Fgf-8 expression in the apical ectodermal ridge. The treatment also reduced Fgf-10 expression in the mesenchyme. Moreover 2-O-sulfated HS, normally abundant in the basement membranes and mesoderm under ectoderm in limb buds, was significantly reduced in the treated buds. Phosphorylation levels of ERK and Akt were up-regulated in such truncated buds. Thus, we have shown for the first time that 2-O-sulfation of HS is essential for the FGF signaling required for limb bud development and outgrowth.

Hyaluronan in limb morphogenesis

Hyaluronan (HA) is a large glycosaminoglycan that is not only a structural component of extracellular matrices, but also interacts with cell surface receptors to promote cell proliferation, migration, and intracellular signaling. HA is a major component of the extracellular matrix of the distal subapical mesenchymal cells of the developing limb bud that are undergoing proliferation, directed migration, and patterning in response to the apical ectodermal ridge (AER), and has the functional potential to be involved in these processes. Here we show that the HA synthase Has2 is abundantly expressed by the distal subridge mesodermal cells of the chick limb bud and also by the AER itself. Has2 expression and HA production are downregulated in the proximal central core of the limb bud during the formation of the precartilage condensations of the skeletal elements, suggesting that downregulation of HA may be necessary for the close juxtaposition of cells and the resulting cell-cell interactions that trigger cartilage differentiation during condensation. Overexpression of Has2 in the mesoderm of the chick limb bud in vivo results in the formation of shortened and severely malformed limbs that lack one or more skeletal elements. Skeletal elements that do form in limbs overexpressing Has2 are reduced in length, exhibit abnormal morphology, and are positioned inappropriately. We also demonstrate that sustained HA production in micromass cultures of limb mesenchymal cells inhibits formation of precartilage condensations and subsequent chondrogenesis, indicating that downregulation of HA is indeed necessary for formation of the precartilage condensations that trigger cartilage differentiation. Taken together these results suggest involvement of HA in various aspects of limb morphogenesis.

Catalase characterization and implication in bleaching of a symbiotic sea anemone

Symbiotic cnidarians are marine invertebrates harboring photosynthesizing microalgae (named zooxanthellae), which produce great amounts of oxygen and free radicals upon illumination. Studying antioxidative balance is then crucial to understanding how symbiotic cnidarians cope with ROS production. In particular, it is suspected that oxidative stress triggers cnidarian bleaching, i.e., the expulsion of zooxanthellae from the animal host, responsible for symbiotic cnidarian mass mortality worldwide. This study therefore investigates catalase antioxidant enzymes and their role in bleaching of the temperate symbiotic sea anemone Anemonia viridis. Using specific separation of animal tissues (ectoderm and endoderm) from the symbionts (zooxanthellae), spectrophotometric assays and native PAGE revealed both tissue-specific and activity pattern distribution of two catalase electrophoretypes, E1 and E2. E1, expressed in all three tissues, presents high sensitivity to the catalase inhibitor aminotriazole (ATZ) and elevated temperatures. The ectodermal E1 form is responsible for 67% of total catalase activity. The E2 form, expressed only within zooxanthellae and their host endodermal cells, displays low sensitivity to ATZ and relative thermostability. We further cloned an ectodermal catalase, which shares 68% identity with mammalian monofunctional catalases. Last, 6 days of exposure of whole sea anemones to ATZ (0.5 mM) led to effective catalase inhibition and initiated symbiont expulsion. This demonstrates the crucial role of this enzyme in cnidarian bleaching, a phenomenon responsible for worldwide climate-change-induced mass mortalities, with catastrophic consequences for marine biodiversity.

Relative contribution of cell contact pattern, specific PKC isoforms and gap junctional communication in tight junction assembly in the mouse early embryo

In mouse early development, cell contact patterns regulate the spatial organization and segregation of inner cell mass (ICM) and trophectoderm epithelium (TE) during blastocyst morphogenesis. Progressive membrane assembly of tight junctional (TJ) proteins in the differentiating TE during cleavage is upregulated by cell contact asymmetry (outside position) and suppressed within the ICM by cell contact symmetry (inside position). This is reversible, and immunosurgical isolation of the ICM induces upregulation of TJ assembly in a sequence that broadly mimics that occurring during blastocyst formation. The mechanism relating cell contact pattern and TJ assembly was investigated in the ICM model with respect to PKC-mediated signaling and gap junctional communication. Our results indicate that complete cell contact asymmetry is required for TJ biogenesis and acts upstream of PKC-mediated signaling. Specific inhibition of two PKC isoforms, PKCdelta and zeta, revealed that both PKC activities are required for membrane assembly of ZO-2 TJ protein, while only PKCzeta activity is involved in regulating ZO-1alpha+ membrane assembly, suggesting different mechanisms for individual TJ proteins. Gap junctional communication had no apparent influence on either TJ formation or PKC signaling but was itself affected by changes of cell contact patterns. Our data suggest that the dynamics of cell contact patterns coordinate the spatial organization of TJ formation via specific PKC signaling pathways during blastocyst biogenesis.

Induction of ectopic olfactory structures and bone morphogenetic protein inhibition by Rossy, a group XII secreted phospholipase A2

The secreted phospholipases A(2) (sPLA(2)s) comprise a family of small secreted proteins with the ability to catalyze the generation of bioactive lipids through glycophospholipid hydrolysis. Recently, a large number of receptor proteins and extracellular binding partners for the sPLA(2)s have been identified, suggesting that these secreted factors might exert a subset of their broad spectrum of biological activities independently of their enzymatic activity. Here, we describe an activity for the sPLA(2) group XII (sPLA(2)-gXII) gene during Xenopus laevis early development. In the ectoderm, sPLA(2)-gXII acts as a neural inducer by blocking bone morphogenetic protein (BMP) signaling. Gain of function in embryos leads to ectopic neurogenesis and to the specification of ectopic olfactory sensory structures, including olfactory bulb and sensory epithelia. This activity is conserved in the Drosophila melanogaster, Xenopus, and mammalian orthologs and appears to be independent of the lipid hydrolytic activity. Because of its effect on olfactory neurogenesis, we have renamed this gene Rossy, in homage to the Spanish actress Rossy de Palma. We present evidence that Rossy/sPLA(2)-gXII can inhibit the transcriptional activation of BMP direct-target gene reporters in Xenopus and mouse P19 embryonic carcinoma cells through the loss of DNA-binding activity of activated Smad1/4 complexes. Collectively, these data represent the first evidence for signaling cross talk between a secreted phospholipase A(2) and the BMP/transforming growth factor beta pathways and identify Rossy/sPLA(2)-gXII as the only factor thus far described which is sufficient to induce anterior sensory neural structures during vertebrate development.

Impact of egg storage on carbonic anhydrase activity during early embryogenesis in the turkey

Carbonic anhydrase is an enzyme that plays important roles in the conversion of carbon dioxide to bicarbonate, acid-base balance, and in subembryonic fluid formation in the early Japanese quail embryo. While turkey egg storage longer than 10 d is known to increase the rate of embryo mortality, little is known of the biological mechanisms that contribute to this phenomenon. In this study, we examined the impact of turkey egg storage on carbonic anhydrase activity in the freshly laid egg through 72 h of incubation. Carbonic anhydrase activity, which was not affected by egg storage for 21 d at 18 degrees C, was first observed in the germ wall, that area of yolk subjacent to the area opaca, after 24 h incubation. By 48 and 72 h, the yolk sac had formed with the yolk sac endoderm and was strongly positive for carbonic anhydrase. In contrast, mesodermal and ectodermal layers were negative. Our observations support recent studies showing carbonic anhydrase activity associated with the endodermal cell of the yolk sac in Japanese quail embryos and that such activity appears to be involved with subembryonic fluid formation in the turkey. This work also demonstrated that if an embryo survives cold egg storage, carbonic anhydrase activity does not appear to be affected.

Immunohistochemical Analysis of Protein Gene Product 9.5, a Ubiquitin Carboxyl-terminal Hydrolase, during Placental and Embryonic Development in the Mouse

Protein gene product 9.5 (PGP9.5) is expressed at high level in the neural and neuroendocrine systems. We investigated the localization and degree of expression of PGP9.5 in the developing mouse placenta and embryo at 6.5, 10.5 and 14 days of gestation using an immunohistochemical technique. At 6.5 days of gestation PGP9.5 was detected at various levels in decidual and primary trophoblast giant cells in the placenta, and in embryonic ectodermal cells in the embryo. At 10.5 and 14 days of gestation PGP9.5 was expressed at moderate to strong levels in neurons in the embryo, but rarely in the placenta. These findings suggest that the protein may play a significant role in implantation and placental development, and differentiation of embryonic ectoderm.

PKCgamma regulates syndecan-2 inside-out signaling during xenopus left-right development

The transmembrane proteoglycan syndecan-2 cell nonautonomously regulates left-right (LR) development in migrating mesoderm by an unknown mechanism, leading to LR asymmetric gene expression and LR orientation of the heart and gut. Here, we demonstrate that protein kinase C gamma (PKCgamma) mediates phosphorylation of the cytoplasmic domain of syndecan-2 in right, but not left, animal cap ectodermal cells. Notably, both phosphorylation states of syndecan-2 are obligatory for normal LR development, with PKCgamma-dependent phosphorylated syndecan-2 in right ectodermal cells and nonphosphorylated syndecan-2 in left cells. The ectodermal cells contact migrating mesodermal cells during early gastrulation, concurrent with the transmission of LR information. This precedes the appearance of monocilia and is one of the earliest steps of LR development. These results demonstrate that PKCgamma regulates the cytoplasmic phosphorylation of syndecan-2 and, consequently, syndecan-2-mediated inside-out signaling to adjacent cells.

Sequential induction of embryonic and adult forms of glutamic acid decarboxylase during in vitro-induced neurogenesis in cloned neuroectodermal cell-line, NE-7C2

The expression of different forms of glutamate decarboxylases and GABA was investigated in the course of retinoic acid-induced neuronal differentiation of NE-7C2 cell-line established from brain vesicles of 9-day-old mouse embryos lacking functional p53 gene. Non-induced NE-7C2 cells expressed embryonic GAD mRNAs with a low level of embryonic GAD25 protein and did not contain detectable amounts of GABA. Addition of 10(-6) M retinoic acid induced the expression of N-tubulin and a significant increase in the level of embryonic GAD messages and GAD25 protein in early stage differentiating neurones. The enzymatically active embryonic GAD44 was detected at later stages of induction in neurone-like cells and showed a maximum of expression at the time of neurite elongation and network formation. With the advance of neuronal maturation, the expression of embryonic forms declined while the adult GAD65 and GAD67 transcripts became dominant. GABA-containing neurones were first demonstrated on the sixth day of induction coinciding with the peak of GAD44 expression and the beginning of GAD65 expression. The sequential induction of different GAD forms and the stage-dependent GABA synthesis in NE-7C2 cells is highly reminiscent of the temporal pattern found in vivo and suggests that these processes might be involved in the differentiation of neuronal progenitors.

Xenopus adenine nucleotide translocase mRNA exhibits specific and dynamic patterns of expression during development

We report the isolation and characterization of the Xenopus homolog to human T1 ANT (adenine nucleotide translocase). The 1290-nucleotide sequence contains initiation and termination signals, and encodes a conceptual protein of 298 amino acids. The sequence shares high amino acid identity with the mammalian adenine translocases. The transcript is present in unfertilized eggs, and it is expressed at higher levels during formation of the antero-posterior dorsal axis in embryos. Although low levels are expressed constitutively except in endodermal cells, adenine nucleotide translocase (ANT) expression is dynamically regulated during neurulation. At this stage, expression in ectoderm rapidly diminishes as the neural folds form, and then ANT expression increases slightly in mesoderm. At the culmination of neurulation, the neural tube briefly expresses ANT, and thereafter its expression predominates in the somitic mesoderm and also the chordoneural hinge. In addition, ANT expression is particularly high in the prosencephalon, the mesencephalon, the branchial arches, eye, and the otic vesicle. Treatment of embryos with retinoic acid has the effect of diminishing constitutive expression of ANT, but microinjection studies demonstrate that immediate and local repression cannot be induced in dorsal structures.

Regulation of MAP kinase by the BMP-4/TAK1 pathway in Xenopus ectoderm

Bone morphogenetic protein-4 (BMP-4) induces epidermis and represses neural fate in Xenopus ectoderm. Our previous findings implicate p42 Erk MAP kinase (MAPK) in the response to neural induction. We have examined the effects of BMP-4 on MAPK activity in gastrula ectoderm. Expression of a dominant negative BMP-4 receptor resulted in a 4.5-fold elevation in MAPK activity in midgastrula ectoderm. MAPK activity was reduced in ectoderm expressing a constitutively active BMP-4 receptor, or ectoderm treated with BMP-4 protein in the presence or absence of cycloheximide. Overexpression of TAK1 led to a reduction in MAPK activity in early gastrula ectoderm. The inhibitory effects of TAK1 could be reversed by 1 microM SB 203580, a p38 inhibitor. Treatment of isolated ectoderm with SB 203580 led to expression of otx2, NCAM, and noggin. Western blot analyses indicated that the BMP-4 pathway does not activate JNKs in ectoderm. Our findings indicate that BMP-4 inhibits ectodermal MAPK activity through a TAK1/p38-type pathway. MAPK has been shown to inactivate Smad1. Thus, our results suggest that BMP-4 and MAPK pathways are mutually antagonistic in Xenopus ectoderm, and that interactions between these pathways may govern the choice between epidermal and neural fate.

Dynamic expression of a glutamate decarboxylase gene in multiple non-neural tissues during mouse development

BACKGROUND

Glutamate decarboxylase (GAD) is the biosynthetic enzyme for the neurotransmitter gamma-aminobutyric acid (GABA). Mouse embryos lacking the 67-kDa isoform of GAD (encoded by the Gad1 gene) develop a complete cleft of the secondary palate. This phenotype suggests that this gene may be involved in the normal development of tissues outside of the CNS. Although Gad1 expression in adult non-CNS tissues has been noted previously, no systematic analysis of its embryonic expression outside of the nervous system has been performed. The objective of this study was to define additional structures outside of the central nervous system that express Gad1, indicating those structures that may require its function for normal development.

RESULTS

Our analysis detected the localized expression of Gad1 transcripts in several developing tissues in the mouse embryo from E9.0-E14.5. Tissues expressing Gad1 included the tail bud mesenchyme, the pharyngeal pouches and arches, the ectodermal placodes of the developing vibrissae, and the apical ectodermal ridge (AER), mesenchyme and ectoderm of the limb buds.

CONCLUSIONS

Some of the sites of Gad1 expression are tissues that emit signals required for patterning and differentiation (AER, vibrissal placodes). Other sites correspond to proliferating stem cell populations that give rise to multiple differentiated tissues (tail bud mesenchyme, pharyngeal endoderm and mesenchyme). The dynamic expression of Gad1 in such tissues suggests a wider role for GABA signaling in development than was previously appreciated.

Developmental characterization and chromosomal mapping of a LacZ transgene expressed in the mouse apical ectodermal ridge

The apical ectodermal ridge (AER) has an essential role in limb morphogenesis involving the specification of the proximal-distal axis of the limb. During the analysis of transgenic mice that harbor a LacZ transgene, we detected strong expression of beta-galactosidase within the AER of developing embryos. In this mouse line, called Z16, the bacterial LacZ gene is linked to a Herpes simplex virus immediate early promoter that is normally silent in mice. Embryos from other independent mouse lines harboring the same DNA construct exhibited no AER specific staining. Thus, it appears that the LacZ transgene in the Z16 line is expressed in the AER in response to regulatory influences from genomic DNA flanking the integration site. By fluorescent in situ hybridization, the transgene insertion site was mapped to chromosome 12. Hemizygous and homozygous transgenic mice appear normal and are fertile. AER specific beta-galactosidase staining was detected by 9.5 days post coitum in the forelimb and hindlimb bud. beta-galactosidase staining could be seen throughout the development of the limbs up to 14.5 days post coitum when expression was restricted to the distal-most regions of the digits of the hindlimbs. The loss of beta-galactosidase staining between digits correlated with the onset of programmed cell death, or apoptosis, in the digit interzones. LacZ expression in this transgenic line represents a useful marker for studying AER function in limb specification during mouse embryogenesis.

Tissue-specific localization of cytochrome P450 aromatase in the equine embryo by in situ hybridization and immunocytochemistry

Estrogen production by the preimplantation equine embryo is presumed to be important in maternal-conceptus communication in the mare. The synthesis of C(18) estrogens from C(19) androgens requires cytochrome P450 aromatase (P450(arom)) in the conceptus, but little information is available on the specific tissue location or potential developmental patterns of expression for the horse. The goal of this research was to localize P450(arom) in the equine conceptus by immunocytochemistry and in situ hybridization. Intact blastocyst-stage embryos were collected by nonsurgical flush on Days 12-15 of pregnancy, fixed in 4% paraformaldehyde, and paraffin-embedded. Aromatase protein was localized using rabbit anti-human placental aromatase antiserum with a detection system utilizing peroxidase and 3-amino-9-ethylcarbazole. For in situ hybridization, tissue sections were incubated with sense or antisense [(35)S]UTP-labeled cRNA probes prepared from equine aromatase cDNA. Aromatase protein and transcript were abundant in the extraembryonic trophectoderm but absent from embryonic ectoderm. No P450(arom) expression was detected in abembryonic endoderm or mesoderm. Aromatase expression was demonstrated in the endoderm beneath the disc (hypoblast). This pattern of P450(arom) expression in the equine blastocyst closely resembles that seen transiently in the porcine embryo, suggesting that regulatory mechanisms conferring tissue specificity may be conserved.

The SH2 tyrosine phosphatase shp2 is required for mammalian limb development

The tyrosine phosphatase Shp2 is recruited into tyrosine-kinase signalling pathways through binding of its two amino-terminal SH2 domains to specific phosphotyrosine motifs, concurrent with its re-localization and stimulation of phosphatase activity. Shp2 can potentiate signalling through the MAP-kinase pathway and is required during early mouse development for gastrulation. Chimaeric analysis can identify, by study of phenotypically normal embryos, tissues that tolerate mutant cells (and therefore do not require the mutated gene) or lack mutant cells (and presumably require the mutated gene during their developmental history). We therefore generated chimaeric mouse embryos to explore the cellular requirements for Shp2. This analysis revealed an obligatory role for Shp2 during outgrowth of the limb. Shp2 is specifically required in mesenchyme cells of the progress zone (PZ), directly beneath the distal ectoderm of the limb bud. Comparison of Ptpn11 (encoding Shp2)-mutant and Fgfr1 (encoding fibroblast growth factor receptor-1)-mutant chimaeric limbs indicated that in both cases mutant cells fail to contribute to the PZ of phenotypically normal chimaeras, leading to the hypothesis that a signal transduction pathway, initiated by Fgfr1 and acting through Shp2, is essential within PZ cells. Rather than integrating proliferative signals, Shp2 probably exerts its effects on limb development by influencing cell shape, movement or adhesion. Furthermore, the branchial arches, which also use Fgfs during bud outgrowth, similarly require Shp2. Thus, Shp2 regulates phosphotyrosine-signalling events during the complex ectodermal-mesenchymal interactions that regulate mammalian budding morphogenesis.

[Immunohistochemical characterisation of surgically excised choroidal neovascularisation in age-related macular degeneration]

AIM

The objective of the study was to gather further information about the pathogenesis of choroidal neovascularisations (CNV), which is still not clearly understood, and to establish criteria for making decisions on a appropriate therapy. Immunohistochemical characteristation should allow a more comprehensive evaluation of cellular components of the membranes and their functional role.

PATIENTS AND METHODS

In 29 patients (16 women, 13 men) with age-related macular degeneration ranging in age from 46 to 91 years (mean age, 76.4 years), CNV were excised by pars-plana vitrectomy. Sections were stained with hematoxylin-eosin (HE) and periodic acid-Schiff (PAS) and examined by light microscopy. For the immunohistochemical characterisation of the surgical specimens the following anti-genetic determinants were used: glial fibrillary acid protein (GFAP) for glial cells, synaptophysin for neuronal cells, neuron-specific enolase (NSE) for neuronal and neuroectodermal cells, CD 31 for endothelial cells and pancytokeratin (KL1) for cells of the retinal pigment epithelium (RPE). Cells undergoing apoptosis were labeled with the TUNEL technique.

RESULTS

22 (76%) surgical specimens showed TUNEL positive cells in the connective tissue, vascular endothelium and retinal pigment epithelium. Positive immunostaining of neuronal antigenetic determinants was found for glial fibrillary acid protein in 22 patients (76%), for synaptophysin in 28 patients (97%) and for neuron-specific enolase in 21 patients (72%) CNV. The epithelial marker KL1 was positive in 28 patients (97%) and the endothelial marker CD 31 in 20 patients (69%).

CONCLUSION

The immunohistochemical analyses of CNV showed that in the majority of cases during the excision of choroidal neovascularizations in addition to scar tissue and connective tissue also parts of the native retinal pigment epithelium and of the neurosensory retina are removed which is only partly visible with standard staining techniques. These findings suggest that the mostly not satisfying postoperative results are partly due to the damage of neuronal cells and a partial loss of the retinal pigment epithelium. Apoptosis as a regulating mechanism in choroidal neovascularization. The variable appearence of apoptosis suggests that it is possibly related to the degree of activity of CNV.

Maternal and zygotic expression of the endoderm-specific alkaline phosphatase gene in embryos of the ascidian, Halocynthia roretzi

Alkaline phosphatase (AP) activity is expressed by endodermal cells of ascidian larvae. It was reported previously that the expression of AP activity is resistant to treatment with actinomycin D, a transcription inhibitor that inhibits the appearance of several other tissue-specific molecules and morphological markers of tissue formation in developing ascidians. The resistance of AP expression to actinomycin D treatment suggests that endodermal AP activity does not depend on zygotic transcription and that its appearance is mediated by the translational activation of maternal AP mRNA present in ascidian eggs. However, it was also shown that anucleate merogons do not develop AP activity. To directly examine whether maternal AP transcripts are present in the cytoplasm of eggs, we isolated a cDNA of an endoderm-specific AP in Halocynthia roretzi and examined the temporal and spatial expressions of this gene during embryogenesis using Northern blots and in situ hybridization. Maternal AP transcripts were detected in oocytes, cleaving-stage embryos, and in gastrulae, and endoderm-specific AP transcripts dramatically increased about 14 times from the neurula stage to the larval stage in endoderm precursor cells. These results suggest that the differentiation of endoderm is primarily correlated with the activation of zygotic transcription of the AP gene, presumably by egg cytoplasmic factors, similar to how muscle and epidermis are believed to develop.

Na/K-ATPase-mediated 86Rb+ uptake and asymmetrical trophectoderm localization of alpha1 and alpha3 Na/K-ATPase isoforms during bovine preattachment development

This study evaluated Na/K-ATPase alpha 1- and alpha 3-subunit isoform polypeptide expression and localization during bovine preattachment development. Na/K-ATPase cation transport activity from the one-cell to blastocyst stage was also determined by measuring ouabain-sensitive 86Rb+ uptake. Both alpha1- and alpha 3-subunit polypeptides were detected by immunofluorescence to encircle the entire cell margins of each blastomere of inseminated zygotes, cleavage stage embryos, and morulae. Immunofluorescent localization of alpha1-subunit polypeptide in bovine blastocysts revealed an alpha1 immunofluorescence signal confined to the basolateral membrane margins of the trophectoderm and encircling the cell periphery of each inner cell mass (ICM) cell. In contrast, alpha 3-subunit polypeptide immunofluorescence was localized primarily to the apical cell surfaces of the trophectoderm with a reduced signal present in basolateral trophectoderm regions. There was no apparent alpha 3-subunit signal in the ICM. Analysis of 86Rb+ transport in vitro demonstrated ouabain-sensitive activity throughout development from the one-cell to the six- to eight-cell stage of bovine development. 86Rb+ uptake by morulae (day 6 postinsemination) did not vary significantly from uptake detected in cleavage stage embryos; however, a significant increase was measured at the blastocyst stage (P < 0.05). Treatment of embryos with cytochalasin D (5 micrograms/ml) did not influence 86Rb+ uptake in cleavage stage embryos. Cytochalasin D treatment however was associated with a significant rise in ion transport in morulae and blastocysts (13.49 and 61.57 fmol/embryo/min, respectively) compared to untreated controls (2.65 and 22.83 fmol/embryo/min, respectively). Our results, for the first time, demonstrate that multiple Na/K-ATPase alpha-subunit isoforms are distributed throughout the first week of mammalian development and raise the possibility that multiple isozymes of the Na/K-ATPase contribute to blastocyst formation.

MAP kinase in situ activation atlas during Drosophila embryogenesis

Receptor tyrosine kinases (RTKs) and the signaling cascades that they trigger play central roles in diverse developmental processes. We describe the capacity to follow the active state of these signaling pathways in situ. This is achieved by monitoring, with a specific monoclonal antibody, the distribution of the active, dual phosphorylated form of MAP kinase (ERK). A dynamic pattern is observed during embryonic and larval phases of Drosophila development, which can be attributed, to a large extent, to the known RTKs. This specific detection has enabled us to determine the time of receptor activation, visualize gradients and boundaries of activation, and postulate the distribution of active ligands. Since the antibody was raised against the phosphorylated form of a conserved ERK peptide containing the TEY motif, this approach is applicable to a wide spectrum of multicellular organisms.

Localization of MAP kinase activity in early Xenopus embryos: implications for endogenous FGF signaling

We have used a sensitive assay for MAP kinase activity to investigate the role of endogenous fibroblast growth factor (FGF)-activated MAP kinase in early Xenopus embryonic patterning. MAP kinase activity is low during cleavage stages and increases significantly during gastrulation. The temporal profile of this activity correlates well with the expression pattern of Xenopus eFGF. Spatially, MAP kinase activity is lowest in animal pole tissue and higher in vegetal pole cells and the marginal zone. Endogenous MAP kinase activity is FGF receptor-dependent, demonstrating that FGF signaling is active in all three germ layers of the early embryo. This activity is necessary for normal expression of Mix.1, a mesoendodermal marker, in the endoderm as well as in the mesoderm, indicating that MAP kinase plays a functional role in patterning of both of these germ layers. Spatial and temporal changes in MAP kinase activation during gastrulation also suggest a role for FGF signaling in this process. In addition, we find that embryonic wounding during dissection results in significant stimulation of this pathway, providing a possible explanation for earlier observations of effects of surgical manipulation on cell fate in early embryos.

Expression of 72-kDa gelatinase (matrix metalloproteinase-2) in the developing mouse craniofacial complex

Tissue remodelling is an important feature during embryogenesis. Although the matrix metalloproteinases are believed to participate in these processes, the relation between matrix metalloproteinases and tissue remodelling during craniofacial morphogenesis remains unclear. The purpose of the study was to look for the presence of enzymes involved in extracellular matrix degradation during craniofacial morphogenesis. Protein expression of the matrix metalloproteinase, 72-kDa gelatinase (matrix metalloproteinase-2, gelatinase A, 72-kDa type IV collagenase) was studied by gelatine zymography and by indirect immunofluorescence with conventional and confocal microscopy. In the anterior region of the developing mouse face, 72-kDa gelatinase was labelled mainly in the tips and peripheral regions of the nasal and facial prominences. Upon contact and fusion of the prominences, the staining was intensely localized to the zone of the fusion and the tips and peripheral regions of the nasal prominences and the maxilla. The labelling of 72-kDa gelatinase was also present in the peripheral regions of the mandible, second branchial arch, and the face around the developing eye. However, during lens vesicle formation, the staining of 72-kDa gelatinase was absent in the invaginated lens ectoderm. After the lens had completely detached from the surface ectoderm, the staining was resumed in the corneal epithelium and mesenchyme. Gelatine zymography was used to confirm the presence of active and latent 72-kDa gelatinase in the developing mouse craniofacial complex. Collectively, these data indicate that 72-kDa gelatinase may play a significant part in localized tissue remodelling during craniofacial morphogenesis and the aberrant expression or function of the enzyme could be involved in causing facial abnormalities.

Shark, a Src homology 2, ankyrin repeat, tyrosine kinase, is expressed on the apical surfaces of ectodermal epithelia

Tyrosine kinases, ankyrin repeats, and Src homology 2 domains play central roles in developmental processes. The cloning of a cDNA for Shark, a single protein that possesses all three domains, is described. During Drosophila embryogenesis, Shark is expressed exclusively by ectodermally derived epithelia and is localized preferentially to the apical surface of these cells. This apical localization persists, even as tissues undergo complex invaginations, moving from the external surface of embryos to form internal structures, but expression is lost when cells lose their polarity. This pattern closely mimics the expression of Crumbs, a protein necessary for proper organization of ectodermal epithelia. Shark's structure and localization pattern suggest that it functions in a signaling pathway for epithelial cell polarity, possibly transducing the Crumbs signal.

A maternal genetic effect on the composition of mouse aggregation chimaeras

Two series of 12 1/2 day mouse chimaeric conceptuses were produced by aggregating (C57BL x CBA)F2 strain preimplantation embryos with embryos that differed at the Gpi-1s locus that encodes glucose phosphate isomerase, GPI-1. The composition of individual issues was evaluated by quantitative electrophoresis to estimate the % GPI-1A in the chimaeric tissue containing GPI-1A and GPI-1B. In one series of chimaeras, the GPI-1A cells were derived from a backcross between inbred BALB/c strain females and (BC x BALB/c)F1 males, where BC is the partly congenic strain C57BL/Ola.AKR-Gpi-lsa,c/Ws. In the other series of chimaeras, the GPI-1A cells were derived from the reciprocal backcross between (BC x BALB/c)F1 females and inbred BALB/c strain males. The [(BC x BALB/c)F1 female x BALB/c male]<==>(C57BL x CBA)F2 series of chimaeras was reasonably balanced so that GPI-1A and GPI-1B cells were fairly equally represented in the foetuses, placentas and extraembryonic membranes (tissue means: 37-51% GPI-1A). This series did not differ significantly in composition from an earlier series of (BC x BALB/c)F2<==>(C57BL x CBA)F2 chimaeras. However, the [BALB/c female x (BC x BALB/c)F1 male]<==>(C57BL x CBA)F2 series of chimaeras was unbalanced, with mean tissue compositions (28-33% GPI-1A) that were intermediate between the above two balanced series and the unbalanced (BALB/c x BALB/c)<==>(C57BL x CBA)F2 series (tissue means: 14-22% GPI-1A), that was studied previously. Thus, both (BALB/c x BALB/c) and [BALB/c x (BC x BALB/c)F1] embryos contributed less to the tissues of chimaeric conceptuses than either (BC x BALB/c)F2 or [BC x BALB/c)F1 x BALB/c] embryos. This implies that embryos from BALB/c mothers contributed less to the tissues of chimaeric conceptuses than embryos from (BC x BALB/c)F1 mothers. We, therefore, conclude that a maternal genetic effect is responsible for some of the differences in composition among the four groups of chimaeras. This maternal effect must act before the 8-cell stage but it is not yet known whether it is mediated via cytoplasmic inheritance, genomic imprinting or by the reproductive tract. Evidence that a maternal effect retards preimplantation development of embryos from BALB/c females is reviewed and the possibility that this might cause them to contribute poorly to chimaeric conceptuses when aggregated with more precociously developing embryos is discussed.

Alkaline phosphatase staining of pig and sheep epiblast cells in culture

To define better the characteristics of pig and sheep epiblast cells in culture, the cells were tested for the presence of alkaline phosphatase (AP), a biochemical marker characteristic of mouse embryonic stem cells. Pig and sheep epiblast cells were positive for AP staining both at isolation from the blastocyst and after primary in vitro culture. The innermost portion of the attendant endoderm surrounding the epiblast was also positive for AP staining during primary culture. AP staining was lost upon differentiation or senescence of the epiblast cells. Also, all differentiated epiblast-derived cell cultures were negative for AP staining, with the exception of neuron-like cultures. Epiblast-like cells were cultured from day 10 (pig) and day 13 (sheep) embryonic discs, and these cells were also AP positive until they differentiated. Trophectoderm-endoderm-like cells from embryonic discs were AP negative or weakly positive. AP is a convenient marker for undifferentiated pig and sheep epiblast cells in culture when used in conjunction with cell morphology analysis.

Proximal cis-acting elements cooperate to set Hoxb-7 (Hox-2.3) expression boundaries in transgenic mice

The Hox genes have been proved to be instrumental in establishing the positional identity of cells along the embryonic anteroposterior (A-P) axis. Studying the regulation of these genes is a first step toward elucidating the molecular basis of regionalization during embryogenesis. We report here on the identification of cis-acting elements controlling the expression of Hoxb-7 (Hox-2.3). We show that elements driving A-P restricted gene expression are located within the 3.5 kb proximal upstream sequences of the Hoxb-7 gene. A deletion analysis provides evidence for at least three cis-acting control elements upstream from Hoxb-7, and for cooperative interactions between some of these elements in generating the A-P restricted transgenic pattern. One element, conferring by itself Hox-like expression boundaries to the transgene, has been studied in more detail and found to act in an orientation-and promoter-dependent manner. Together the 3.5 kb sequences proximal to Hoxb-7 mediate A-P restricted Hoxb-7/lacZ gene expression in a domain showing rostral boundaries more posterior than those of Hoxb-7. The evolution throughout embryogenesis of the expression pattern of a transgene carrying these sequences has been analysed and shown to mimick that of the endogenous gene, except for a slight delay in the initial expression. We conclude that the transgenes that we tested, spanning a total of 27 kb genomic sequences, do not reproduce all the features of the Hoxb-7 expression pattern. The differences in expression between Hoxb-7 and the transgenes may reveal an aspect of the Hox regulation for which either remote cis-acting control elements and/or gene clustering is required. Additional features that may have favoured maintenance of clustered organisation during evolution are partial overlap of transcription units with the regulatory regions of the neighbouring genes, and cis-regulatory interactions between multiple Hox genes: not only do cis-acting control elements of the Hoxb-7 gene map in the 3′ untranslated sequences of the Hoxb-8 (Hox-2.4) gene, but our experiments suggest that Hoxb-7 control sequences modulate expression of the Hoxb-8 gene as well.

Protein kinase C isozymes have distinct roles in neural induction and competence in Xenopus

The restricted ability of embryonic tissue to respond to inductive signals is controlled by a poorly understood phenomenon, termed competence. In Xenopus, dorsal ectoderm is more competent than ventral ectoderm to become induced to neural tissue. We tested whether the Xenopus protein kinase C (PKC) isozymes alpha and beta have a role in neural induction and competence. We found that PKC alpha is predominantly localized in dorsal ectoderm, whereas PKC beta is uniformly distributed. Overexpression of PKC beta conveys a higher propensity for neural differentiation to both dorsal and ventral ectoderm, but their difference in competence remains. However, ectopic expression of PKC alpha elevates the level of neural competence of ventral ectoderm to that of dorsal ectoderm. These data indicate that different PKC isozymes have distinct roles in mediating both neural induction and competence.

Primordial germ cells in the mouse embryo during gastrulation

With the aid of a whole-mount technique, we have detected a small cluster of alkaline phosphatase (ALP)-positive cells in whole mounts of mid-primitive-streak-stage embryos, 7–7 1/4 days post coitum (dpc). Within the cluster, about 8 cells contain a small cytoplasmic spot, intensely stained for ALP activity and possibly associated with an active Golgi complex. The cluster lies just posterior to the definitive primitive streak in the extraembryonic mesoderm, separated from the embryo by the amniotic fold. Towards the end of gastrulation, the number of cells containing the ALP-positive spot rises to between 50 and 80. Thereafter the number of cells in the extraembryonic cluster declines, and similar cells start to be seen in the mesoderm of the primitive streak and then in the endoderm. At 8 dpc, about 125 ALP-stained cells are found, mainly in the hindgut endoderm and also at the base of the allantois, their appearance and location at this stage agreeing closely with previous reports on primordial germ cells (PGCs). Embryos from which the cluster area has been removed at the 7-day stage are devoid of PGCs after culture for 48 h, whereas the excised tissue is rich in PGCs. We argue that the cells in the cluster are indeed primordial germ cells, at a stage significantly earlier than any reported previously. This would indicate that the PGC lineage in the mouse is set aside at least as early as 7 dpc, possibly as one of the first ‘mesodermal’ cell types to emerge, and that its differentiation, as expressed by ALP activity, is gradual.

Characterization of protein kinase C in early Xenopus embryogenesis

Recently, we presented evidence that protein kinase C (PKC) is involved in mediating the endogenous signals that induced competent Xenopus ectoderm to differentiate to neural tissue. We report here that PKC is already strongly activated in neural-induced ectoderm from midgastrula embryos and that this activation runs parallel with an increase in the level of inositol phosphates. We further identify several proteins that are phosphorylated, both in natural neural-induced ectoderm and in TPA-treated ectoderm, suggesting that they are phosphorylated through the PKC route. We found no major changes in PKC activity among different pregastrula stages, including the unfertilized egg. However, PKC isolated from animal, ectodermal cells is highly sensitive to Ca2+ and can be activated by low concentrations, (6–25 microM) of arachidonic acid, while PKC isolated from vegetal, endodermal cells is more insensitive to Ca2+ and cannot be activated by arachidonic acid. These results suggest that different PKC isozymes are present in animal and vegetal cells.

Analysis of cell surface galactosyltransferase activity during mouse trophectodermal differentiation

The ectoplacental cone (EPC) of the Day 7.5 mouse embryo consists of a core of adhesive, proliferating trophoblast cells which transform to invasive trophoblast giant cells during implantation. Adhesive trophoblast cell types express monoclonally defined lactosaminoglycans (LAGs) at the cell surface; transformation to giant cells results in a loss of LAG cell surface expression (H. J. Hathaway and B. S. Babiarz, 1988, Cell Differ. 24, 55-66). LAGs can serve as substrates for cell surface galactosyltransferase (GalTase), providing an adhesive mechanism between a number of different cell types (B. D. Shur, 1984, Mol. Cell. Biochem. 61, 143-158). It was hypothesized that the LAGs in the EPC represented a substrate for a similar GalTase-mediated cell:cell adhesion system. Cell surface GalTase activity was demonstrated on EPC trophoblast on Day 7.5 of development by the incorporation of galactose from exogenous radiolabeled substrate. In 24- to 48-hr EPC trophoblast cultures the enzyme was localized by immunofluorescence to areas of cell:cell contact. Monolayers of differentiated trophoblast giant cells lacked this labeling pattern. The cell surface glycopeptide substrate for GalTase eluted as a single peak with an apparent molecular mass of 15,000 Da. A portion of this material was sensitive to endo-beta-galactosidase digestion, indicating that it contained a LAG structure. Perturbation of the enzyme:substrate complex in 24- to 48-hr EPC outgrowths, with alpha-lactalbumin, uridine 5'-diphosphogalactose, or anti-GalTase antibody, resulted in the disruption of cell:cell contacts. Differentiation to trophoblast giant cells resulted in a loss of sensitivity to surface GalTase perturbation. The results suggest that adhesive EPC trophoblast cells possess a GalTase-mediated cell:cell adhesion system which is downregulated upon differentiation to invasive trophoblast giant cells.

Temporal and spatial analysis of hyaluronidase activity during development of the embryonic chick limb bud

The glycosaminoglycan hyaluronate (HA) appears to play an important role in limb cartilage differentiation. The large amount of extracellular HA accumulated by prechondrogenic mesenchymal cells may prevent the cell-cell and/or cell-matrix interactions necessary to trigger chondrogenesis, and the removal of extracellular HA may be essential to initiate the crucial cellular condensation process that triggers cartilage differentiation. It has generally been assumed that HA turnover during chondrogenesis is controlled by the activity of the enzyme hyaluronidase (HAase). In the present study we have performed a temporal and spatial analysis of HAase activity during the progression of limb development and cartilage differentiation in vivo. We have separated embryonic chick wing buds at several stages of development into well-defined regions along the proximodistal axis in which cells are in different phases of differentiation, and we have examined HAase activity in each region. We have found that HAase activity is clearly detectable in undifferentiated wing buds at stage 18/19, which is shortly following the formation of a morphologically distinct limb bud rudiment, and remains relatively constant throughout subsequent stages of development through stage 27/28, at which time well-differentiated cartilage rudiments are present. Moreover, HAase activity in the prechondrogenic distal subridge regions of the limb at stages 22/23 and 25 is just as high as, or even slightly higher than, it is in proximal central core regions where condensation and cartilage differentiation are progressing. We have also found that limb bud HAase is active between pH 2.2 and 4.5 and is inactive above pH 5.0. This suggests that limb HAase is a lysosomal enzyme and that extracellular HA would have to be internalized to be degraded. These results indicate that the onset of chondrogenesis is not associated with the appearance or increase in activity of HAase. We suggest that possibility that HA turnover may be regulated by the binding and endocytosis of extracellular HA in preparation for its intracellular degradation by lysosomal HAase. Finally, we have found that the apical ectodermal ridge (AER)-containing distal limb bud ectoderm possesses a relatively high HAase activity. We suggest the possibility that a high HAase activity in the AER may ensure a rapid turnover and remodeling of the disorganized HA-rich basal lamina of the AER that might be essential for limb outgrowth.

An early developmental phase of pp60c-src expression in the neural ectoderm

The expression of the normal cellular src protein (pp60c-src) was investigated in the early chick embryo during gastrulation and neurulation by immunoperoxidase staining using antisera, raised against bacterially expressed pp60v-src, that recognizes pp60c-src specifically in normal cells. During gastrulation pp60c-src immunoreactivity appeared primarily in the neural ectoderm and was much less prominent in the mesoderm, endoderm, and nonneural ectoderm. During neurulation pp60c-src immunoreactivity began to disappear from the wall of the closing neural tube so that by the completion of neural tube closure no specific pp60c-src immunoreactivity appeared in any of the neuroepithelial cells composing the neural tube. These studies reveal a developmental phase of pp60c-src expression even earlier than reported previously, when neuroepithelial cells of later embryos undergo terminal neuronal differentiation. These findings raise the possibility that pp60c-src may mediate two different differentiation signals in the neuronal lineage.

Ultrastructural localization of cholinesterase during chondrogenesis and myogenesis in the chick limb bud

Cholinesterase (ChE) is transiently expressed in undifferentiated embryonic cells. In the chick limb bud ChE-activity was found in the apical ectodermal ridge and in the subridge mesenchyme. The reaction was localized in the perinuclear cisterna, in an extensive network of narrow profiles of endoplasmic reticulum (ER), and in the Golgi complex. The chondroblasts emerging from the subridge mesenchyme, also showed strong ChE-activity. During differentiation the enzyme first disappeared from the Golgi zone. Then, the narrow ChE-positive ER was successively replaced by ChE-negative extended rough ER characteristic for the differentiated chondrocyte. The myoblasts showed weak ChE-activity with the same ultrastructural localization as in other mesenchymal cells. After fusion the myotubes exhibited strong ChE-activity in the perinuclear cisterna and the developing sarcoplasmic reticulum. In later stages of myogenesis the myoblasts were closely attached to the myotubes and had lost their ChE-activity. During mitosis of ChE-positive cells, ChE-activity was retained in fragments of perinuclear cisterna and ER. In ChE-active mesenchymal cells and chondroblasts we observed specialized contact zones between ER and plasma membrane. ChE-active cisternae of ER run parallel to the plasma membrane with a gap of approximately 10-15 nm. We discuss a possible function of a cholinergic system during morphogenesis.

Acetylcholinesterase (AChE) and pseudocholinesterase (BuChE) activity distribution pattern in early developing chick limbs

The distribution of acetylcholinesterase (AChE) and pseudocholinesterase (BuChE) activities was studied by histochemical, quantitative and electrophoretical methods during the early development of chick limbs, from stage 16 to stage 32 H.H. (Hamburger & Hamilton, 1951). By quantitative methods, true AChE activity was found, and increased about threefold during the developmental period, together with a smaller amount of BuChE which increased more rapidly in comparison with the AChE activity from stage 25 to 32 H.H. Cholinesterase activity was histochemically localized mainly in interacting tissues, such as the ectoderm (including the apical ectodermal ridge) and the underlying mesenchyme. True AChE was histochemically localized around the nuclei and on the plasma membrane of ectodermal (including AER) and mesenchymal cells, and at the plasma membrane of mesenchymal cell processes reaching the basal lamina between the ectoderm and the mesenchyme. AChE together with BuChE activity was found in the basal lamina between the ectoderm and the mesenchyme, in underlying mesenchymal cells and in deeper mesenchymal cells, especially during their transformation into unexpressed chondrocytes. During limb morphogenesis, the cellular and regional localization of the enzyme activities showed variations depending on the stage of development and on the occurrence of interactions. The possibility of morphogenetic functions of the enzyme id discussed.

Localization of Mg++-dependent adenosine triphosphatase and alkaline phosphatase activities in the postimplantation mouse embryos in day 5 and 6

Mg++-dependent adenosine triphosphatase (Mg-ATPase) and alkaline phosphatase (ALPase) activities were histo- and cytochemically investigated in postimplantation mouse embryos from day 5 to day 6. In day 5 postimplantation embryos, Mg-ATPase activity was detected in the embryonic ectoderm and weakly in the visceral endoderm. Weak ALPase activity was found in the embryonic ectoderm and visceral endoderm. Parietal endoderm, both in day 5 and in day 6 embryos, had very weak or no Mg-ATPase and ALPase activities. Mg-ATPase activity in day 6 embryos was found with the same localization as that in day 5 embryos. No ALPase activity was observed in their embryonic ectoderm. Extraembryonic ectodermal cell mass had the strongest Mg-ATPase activity in these stage embryos. These results suggest that the localization of both enzyme activities in postimplantation mouse embryos is closely related to the morphogenesis. As regards the proamniotic cavity formation, the fact that Mg-ATPase activity was still observed in the embryonic ectoderm in these stages suggests the involvement of active transport system on the production of nascent proamniotic cavity fluid.

Choline acetyltransferase in the chick limb bud

In embryonic tissues a primitive cholinergic system is transiently expressed during morphogenesis. In the chick limb bud expression of the primitive cholinergic system in mesenchyme and central chondrogenic core precedes the appearance of the definitive cholinergic system in nerve and muscle. Here we show that, parallel to the expression of cholinesterase in mesenchyme and chondroblasts, embryonic cells are capable of acetylcholine synthesis. Choline acetyltransferase (ChAT) activity was measured by the radiometric assay of Fonnum (1975).

Preferential paternal X inactivation in extraembryonic tissues of early mouse embryos

The preferential expression of the maternal X chromosome seen in certain extraembryonic membranes of the mouse was studied by investigating the tissues from which these membranes are derived during early development. The electrophoretic variant of the X-coded enzyme PGK-1 (phosphoglycerate kinase) was used to distinguish the expression of the maternal from the paternal X chromosome in heterozygous females. Both the extraembryonic ectoderm and primary endoderm of 6 1/2-day female egg cylinders gave almost exclusive expression of the maternal form of the enzyme whereas the epiblast gave near equal expression of the two parental alleles. No paternal PGK-1 band could be detected in samples of pooled 3 1/2-day blastocysts, but after 3 or 4 days of culture in vitro a faint paternal band was seen in the resultant outgrowths. The activity of the maternal band in these latter samples had increased greatly from that of the blastocysts, consistent with preferential expression of the maternal Pgk-1 allele in the trophoblastic cells of the outgrowths, while both alleles are expressed in inner-cell-mass cells. The results strongly support the idea that non-random X-chromosome expression is due to preferential paternal X inactivation in trophectoderm (from which extraembryonic ectoderm is derived) and in primary endoderm, and not to cell selection.

Ultrastructural localization of carbonic anhydrase in the chorioallantoic membrane by immunocytochemistry

Carbonic anhydrase was localized in the chick embryo chorionic ectoderm at the ultrastructural level by immuno-cytochemistry. Preembedding staining of whole tissue was performed. The enzyme was present in the cytoplasm, on the membranes of apical vesicles, and on the membranes of microvilli in villus cavity cells, cells that may be involved in acid secretion and subsequent dissolution of the egg shell. In sinus covering cells, the enzyme is solely in the cytoplasm. The location of the enzyme in the thin cytoplasmic arms of the sinus covering cells is consistent with the role in nonrespiratory CO2 release.

Histochemical features of hind limb development in Xenopus laevis

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Histochemical observations on developing rat skin

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