Spatial-temporal characteristics of intercellular junctions in early zebrafish and loach embryos before and during gastrulation

 Injections of lucifer yellow and fluorescein dyes into loach (Misgurnus fossilis) and zebrafish (Danio rerio) embryos were used to analyse the intercellular communication via gap junctions (GJs) and their role in morphogenetic processes during the period from early blastula to late gastrula. It is shown that the efficiency of dye transfer between the superficial blastomeres increases by the late blastula stage. Blastomeres of the basal layer, on the other hand, become gradually uncoupled from the yolk cell (YC). This process is spatially uneven and finishes by the late gastrula stage. Prior to it, at the early epiboly stage, a local increase in dye transfer is observed in the circular zone of the blastoderm margin. During gastrulation, GJ communication between blastomeres and the YC in this zone and also in the newly-formed germ ring region (the prospective mesoderm domain) persists for a longer period of time (up to the stage of 60–70% epiboly) than in the remaining part of the basal layer (the prospective ectoderm domain). Taking into account the data on changes in the adhesive properties of blastomeres during normal development and observations on embryos with retarded epiboly, we hypothesize that changes in GJ communication between superficial blastomeres, on one hand, and between basal blastomeres and the YC, on the other, are the consequences of the same, more general morphogenetic process of compaction occurring within the blastoderm, which supports epiboly and is probably responsible for the distinction between mesodermal and ectodermal fates of cells differently located within the forming epithelioid sheet. Received: 18 October 1996 / Accepted: 4 April 1997     

Electrophysiological evidence for low-resistance intercellular junctions in the early chick embryo

Electrophysiological evidence is presented for the exchange of small ions directly between cells interiors, i.e. "electrical coupling," in the early chick embryo. Experiments with intracellular marking show that coupling is widespread, occurring between cells in the same tissue, e.g. ectoderm, notochord, neural plate, mesoderm, and Hensen's node, and between cells in different tissues, e.g. notochord to neural plate, notochord to neural tube, notochord to mesoderm. The coupling demonstrates the presence of specialized low-resistance intercellular junctions as found in other embryos and numerous adult tissues. The results are discussed in relation to recent electron microscopical studies of intercellular junctions in the early chick embryo. The function of the electrical coupling in embryogenesis remains unknown, but some possibilities are considered.     

Induced chromosome aberrations in early embryogenesis of mice

Summary A 28-year-old man, whose infant son died of multiple malformations, was shown to have a balanced 13q-/18q+ translocation. He was phenotypically and mentally normal. Studies of the pedigree revealed the presence of bilateral microtia on the side of the spouse of the proband, transmitted in a dominant mode through four generations. Occasional cells from the proband and his mother exhibited an elongated long arm of a chromosome 16.This work was supported by a grant from the National Swiss Foundation for Scientific Research (Credit No. 3.211.69).Supported by Grant 64-411A from the Ford Foundation Population Program.     

PSF1 is essential for early embryogenesis in mice

Psf1 (partner of sld five 1) forms a novel heterotetramer complex, GINS (Go, Ichi, Nii, and San; five, one, two, and three, respectively, in Japanese), with Sld5, Psf2, and Psf3. The formation of this complex is essential for the initiation of DNA replication in yeast and Xenopus laevis egg extracts. Although all of the components are well conserved in higher eukaryotes, the biological function in vivo is largely unknown. We originally cloned the mouse ortholog of PSF1 from a hematopoietic stem cell cDNA library and found that PSF1 is expressed in blastocysts, adult bone marrow, and testis, in which the stem cell system is active. Here we used the gene-targeting technique to determine the physiological function of PSF1 in vivo. Mice homozygous for a nonfunctional mutant of PSF1 died in utero around the time of implantation. PSF1-/- blastocysts failed to show outgrowth in culture and exhibited a cell proliferation defect. Our data clearly indicate that PSF1 is required for early embryogenesis.     

Mesothelial intercellular junctions and pathways

Summary Freeze-etch preparations of mesothelial cells taken from the peritoneum of mouse reveal the presence of vesicles invaginating the apical and the basal cell surfaces. These vesicles are scarcely seen within the cytoplasm. Long tortuous tubular profiles extend for considerable distance within the cytoplasm and are frequently associated with the vesicles. The possible nature and role of the vesicles and the tubules in transport phenomena across the mesothelial barrier, are discussed in relation to the pore theory advanced by physiologists and the stomata concept observed by early German and contemporary anatomists. Occludens junctions of the leaky type are seen though their macular or zonular nature is yet to be established.     

Cell junctions and intercellular communication

Summary We have compared intercellular communication in normal and regenerating rat liver. Gap junctions are greatly reduced in size and numbers 29 to 35 hr after hepatectomy, but we still find some 90% of hepatocytes coupled by electrophysiological criteria. The spread of dyes such as carboxyfluorescein however is very limited in the regenerating organs as compared to the situation in the controls. We show how the apparent discrepancies between morphological and physiological data can be reconciled. We also present a summary of preliminary findings on the biosynthesis of gap junction protein and some of the conclusions one can draw from the sequence of 58 amino acids at the amino terminal of the protein. Presented in the symposium on Molecular and Morphological Aspects of Cell-Cell Communication at the 31st Annual Meeting of the Tissue Culture Association, St. Louis, Missouri, June 1–5, 1980. The original research described was supported by Grants GM 06965 and RR 07003 from the National Institute of Health, and funds from the North-west Area Foundation. David Meyer and Barbara Yancey were the recipients of NIH postdoctoral fellowships (NS 06240 and AM05700). This symposium was supported in part by Contract 263-MD-025754 from the National Cancer Institute and the Fogarty International Center.     

The presence of gap junctions during early Patella embryogenesis: An electron microscopical study

The presence of gap junctions has been examined up to the sixth cleavage in the early Patella embryo. Gap junctions are located all over the blastomere borders. In 2-, 4-, and 8-cell embryos they were also observed at peripheral contacts. The frequency and size of the gap junctions increase at the 32-cell stage. The structure of gap junctions is similar in all stages investigated with hexagonally arranged equal-sized particles (11 nm) having a constant center-to-center spacing (13.0 nm). At the 32-cell stage formation plaques were observed, indicating an increase of gap junctions.     

Elimination of spontaneous and chemically induced chromosome aberrations in mice during early embryogenesis

Summary NMRI mice () were treated with 0.25 mg/kg body weight Trenimon (2,3,5-triethyleneiminobenzoquinone-1,4) in the preovulatory phase just before ovulation. Then they were mated with untreated males.The female mice were dissected 45 h after application of this mutagen. The preimplantation embryos, being in a 2-cell stage, were flushed out of the oviduct and cultured in vitro for 60 h. Of the cultured embryos 87.7% reached the blastocysts stage in the control series, whereas only 49.7% did so in the experiments.Some of the females were dissected on the 14th day post conception (p.c.) and the number of dead and living implants was determined.Furthermore, the 9.5- and 13.5-day-old embryos were cytologically investigated, to determine the frequency of chromosomal aberrations.Of the unfertilized oocytes 76.2% deriving from mice treated with 0.25 mg/kg Trenimon, were aberrant in the stage of metaphase II (Röhrborn and Hansmann, 1971).Comparing Röhrborn's and Hansmann's results (1971) to our own findings a continous elimination of chromosome aberration is clearly to be seen during early embryogenesis. The biological selection takes place in the pre- as well as in the early and late postimplantative phase.     

Unusual features of intercellular junctions in the larvacean Oikopleura dioica

Summary In the pelagic larvacean Oikopleura dioica, the epithelium lining the alimentary tract consists of ciliated and unciliated cell types. The ciliated cells also exhibit an apical border of long microvilli. Between the microvilli, the cellular membrane often projects deeply down into the cytoplasm; the membranes of these invaginations and those of apicolateral interdigitations may be associated with one another by tight junctions. Some of these junctions may be autocellular. The tight junctions are seen by freeze-fracture to be very simple in construction, composed of a single row of intramembranous particles, which may be fused into a P-face ridge. There is a dense cytoplasmic fuzz associated with these tight junctions which may extend into adjoining zonula adhaerens-like regions. The invaginations of the apical membranes are, in addition, associated by gap junctions which may also be autocellular. More conventional homocellular and heterocellular tight and gap junctions occur along the lateral borders of ciliated cells and between ciliated and unciliated cells. These gap junctions possess a reduced intercellular cleft and typical P-face connexons arranged in macular plaques, with complementary E-face pits. Both cell types exhibit extensive stacks of basal and lateral interdigitations. The tight junctions found here are unusual in that they are associated with a dense cytoplasmic fuzz which is normally more characteristic of zonulae adhaerentes.