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PubMedDate not supplied

[Characteristics of the fine structure of embryonic membranes in the spiny-headed worms of the class Eoacanthocephala, by an example of the spiny-headed worm species Neoechinorhynchus crassus].

Five embryonic membranes are found in the spiny-headed worm species Neoechinorhynchus crassus. Four embryonic membranes are analogous to the membranes in all other spiny-headed worms studied, and one membrane is additional. The last is situated between the external and second membranes and is characteristic only for some species of the class Eoacanthocephala. Terminology of the embryonic membranes in connection with their origin and possible functional significance is discussed.

Acanthocephala↗
PubMedDate not supplied

The fine structure of human embryonic stem cells.

The fine structure of human embryonic stem (ES) cell colonies was analysed by transmission electron microscopy (TEM) after 35 passages of in-vitro culture. Most cells formed compact, saucer-shaped colonies with epithelioid cells on the periphery and polygonal cells within the colony. Three morphological types of cells were identified based on their fine structure: undifferentiated cells resembling inner cell mass (ICM) cells of blastocysts; protein-synthesizing cells at the onset of cellular differentiation; and compact masses of secretory cells resembling unicellular goblet cells of the intestine. The predominant cell type was the undifferentiated ES cells resembling ICM cells of blastocysts. These cells had large nuclei containing reticulated nucleoli, well-developed rough endoplasmic reticulum (RER), Golgi complexes, elongated tubular mitochondria, lysosomes and typical centrosomes with centrioles associated with microtubules and microfilaments, organizing the cytoskeleton. Some ES cells have very large nuclei and scanty cytoplasms with fewer organelles. The isolated or attached protein-synthesizing cells at the onset of differentiation had extensive RER and large Golgi complexes. The morphologically differentiated cells formed compact colonies and resembled goblet-like cells in microstructure. They had RER and large Golgi complexes associated with secretory vesicles. The epithelioid cells at the periphery were columnar and largely polarized by centrosomes associated with Golgi complexes. Epithelioid cells in all three categories had specialized cell junctions (desmosomes), anchored by tonofilaments, and surface blebs. Isolated cells were seen on the surface, towards the centre of the colony, and their free surfaces had microvilli and larger blebs. Approximately 3-5% of all cells were mitotic, with typical bipolar spindles organized by centrosomes, pivotally located at the poles, and appeared to resemble typical somatic cells.

Blastocyst↗
PubMed1994

Estimation of gestational age by transvaginal sonographic measurement of greatest embryonic length in dated human embryos.

A prospective descriptive study was carried out to establish reference values for gestational age assessment in the first trimester by measuring embryonic length in dated human embryos, by using transvaginal ultrasound. In 160 pregnant women who had undergone assisted reproductive procedures, 139 singleton embryos and 46 embryos from 21 multiple pregnancies were studied between the 35th and 98th day after the last menstrual period. Transvaginal ultrasound examination, including inspection of embryonic structures and measurement of greatest embryonic length (L), was performed in these women. Estimation of gestational age (t) by measurement of L in singletons is best described by the equation t = 35.72 + 1.082L(1)/(2) + 1.472L - 0.09749L(3)/(2). Mean 95% confidence interval and 95% prediction interval were 4.3 and 9.3 days, respectively. There was no significant change in the estimation curve when multiple measurements in singletons were taken nor when embryos from multiple pregnancies were measured. Accuracy of embryonic age estimation from a single measurement of greatest embryonic length was evaluated.

Journal Article↗
PubMed1981

Hymenolepis nana: the fine structure of the embryonic envelopes.

The fine structure of the envelopes surrounding hatched and unhatched oncospheres of Hymenolepis nana has been investigated by transmission and scanning electron microscopy (SEM), together with light microscope histochemical observations of JB-4 embedded material. The oncosphere is surrounded by 3 layers--the capsule, the outer envelope and the inner envelope, the latter giving rise to the embryophore and the 'oncospheral membrane'. An additional layer--the polar filament layer--lies between the 'oncospheral membrane' and the oncosphere. Shell material is deposited on the capsule as a thin layer. It is secreted by the outer envelope, which degenerates once shell formation is complete. The uterus may also contribute to shell formation. The embryophore forms a thin incomplete and peripheral layer within the inner envelope. In the basal region of this envelope, partial development of an 'oncospheral membrane' takes place, but it does not become detached as a separate layer. The polar filaments, which are characteristic of the oncosphere of H. nana, are derived from the epithelial covering of the oncosphere itself, which delaminates to form a separate polar filament layer. The filaments arise from knob-like projections at opposite poles of this layer. The design of the embryonic envelopes in H. nana show a number of modifications from the basic cyclophyllidean pattern, and these can be related to the demands of its 'direct' life-cycle.

Animals↗
PubMed2003

Zebrafish foxi1 mediates otic placode formation and jaw development.

The otic placode is a transient embryonic structure that gives rise to the inner ear. Although inductive signals for otic placode formation have been characterized, less is known about the molecules that respond to these signals within otic primordia. Here, we identify a mutation in zebrafish, hearsay, which disrupts the initiation of placode formation. We show that hearsay disrupts foxi1, a forkhead domain-containing gene, which is expressed in otic precursor cells before placodes become visible; foxi1 appears to be the earliest marker known for the otic anlage. We provide evidence that foxi1 regulates expression of pax8, indicating a very early role for this gene in placode formation. In addition, foxi1 is expressed in the developing branchial arches, and jaw formation is disrupted in hearsay mutant embryos.

Amino Acid Sequence↗
PubMed2004

Spatial expression of a sunflower SERK gene during induction of somatic embryogenesis and shoot organogenesis.

Organogenesis or somatic embryogenesis can be induced on immature zygotic embryos (IZE) of sunflower depending on the culture conditions. Both morphogenic processes originate from the same group of cells and show identical kinetics. Using real-time PCR and in situ hybridisation, we showed that somatic embryogenesis receptor-like kinase (SERK) transcripts accumulate early after the beginning of the culture in the morphogenic zone of IZE explants whatever the induction conditions used, i.e. organogenic, embryogenic or highly embryogenic conditions. Quantitative analyses failed to show any correlation between the SERK expression level during the period decisive for the orientation of the morphogenic pathway, i.e. the first 2 days of culture, and the type of morphogenesis induced. However, after 2 days of culture on the organogenic medium, the SERK gene expression level was severely down-regulated in the IZE explants. At 4 days of culture, SERK transcripts were no longer detectable by in situ hybridisation in the developing shoot structures whereas they still continued to accumulate in the embryonic structures induced on both embryogenic and highly embryogenic culture media. The significance of these expression analyses was addressed by transfer medium experiments. Results revealed that IZE cultured on the organogenic medium were able to form somatic embryos when transferred on the highly embryogenic medium as long as the SERK transcripts accumulated at a high level in their morphogenic zone, i.e. first 2 days of culture. Passt this delay, explants rapidly lost their embryogenic competence. Indeed, after 4 days of culture on the organogenic medium, IZE were definitely oriented towards shoot organogenesis. Taken together, these data suggest that reactive cells of IZE develop the competence to somatic embryogenesis during the first day of culture whatever the morphogenic induction conditions used.

Culture Media↗