Characterisation of cholinesterase expression during murine embryonic stem cell differentiation.

It is already established that cholinesterases (ChEs) appear in every embryonic blastema at a very early stage of development, independently from innervation. Embryonic butyrylcholinesterase (BChE) is typically found in cells engaged in proliferation processes, while acetylcholinesterase (AChE) is expressed by cells undergoing morphogenetic processes. In order to better define the regulation of cholinesterases during development, we examined their expressions during in vitro differentiation of two murine embryonic stem cell lines by reverse transcription polymerase chain reaction, histochemistry and enzyme activity measurements. AChE and BChE activity and mRNA were present in the undifferentiated stem cells. To test whether the ChEs expression is regulated during differentiation, we employed the embryoid bodies (EBs) culture method, allowing the cells to differentiate, to then collect them at various stages in culture. Interestingly, phases of differentiation were accompanied by increased AChE transcripts; BChE expression was constant, decreasing at later differentiation stages. Cholinesterase activities showed corresponding patterns, with AChE activity increasing at later stages in culture and BChE slightly decreasing. Histochemistry revealed that AChE and BChE activities were mutually exclusive, being expressed by different cell subpopulations. Thus, we have demonstrated that mouse embryonic stem cells express cholinesterases, the enzymes are functional and their expression is regulated during differentiation. Therefore, it appears that their functions under these conditions are not related to synaptic transmission, but for the developmental processes.

Localization by situ hybridization of amplified ribosomal DNA during Xenopus laevis oocyte maturation (a light and electron microscopy study).

The presence of ribosomal DNA has been demonstrated, by light and electron microscopy study of in situ hybridization with 125I-labeled ribosomal RNA, in the Feulgen-positive bodies which appear during maturation in the cytoplasm of Xenopus laevis oocytes. The ultrastructure of these bodies is described.

Amplified ribosomal DNA in meiotic prophase oocyte nuclei of acipenserid fishes.

In situ hybridization has been performed in sections through ovaries ofAcipenser ruthenus andAcipenser güldenstädti in order to detect the rDNA sequences. Hybridization resulted in specific labelling of the "caps" of extrachromosomal DNA present in pachytene oocyte nuclei and of the chromatin granules distributed beneath the nuclear envelope in early diplotene nuclei. In the same sections, the nuclei of all ovarian cells in both species (oogonia, leptotene, and zygotene stage oocytes, follicular cells, connective tissue cells) showed a very low, but similar labelling.Amplification of genes for rRNA thus occurs at the pachytene stage in early oogenesis ofAcipenseridae. No rDNA amplification could be detected in the previous stages.

Presence of rRNA in the heavy bodies of sea urchin eggs. An in situ hybridization study with the electron microscope.

Experimental conditions have been found, in which the presence of rRNA can be demonstrated by in situ hybridization at the electron microscope level in the heavy bodies of sea urchin eggs. The specificity of hybridization has been controlled by ribonuclease digestion and by competition experiments with unlabelled rRNA.

Characterization of yolk DNA from Xenopus laevis oocytes ovulated in vitro.

High molecular weight DNA was isolated from the yolk platelets of Xenopus laevis oocytes ovulated in vitro. Yolk DNA has the same buoyant density in CsCl gradients as mitochondrial and nuclear DNAs, and, like them, it is double-stranded. Yolk DNA behaves like nuclear DNA, and not like mitochondrial DNA, upon renaturation after denaturation. The molecules are always linear. Cytochemical and biochemical controls preclude the possibility that the yolk DNA might be contaminated by nuclear or mitochondrial DNA. We conclude that the yolk DNA is an endogenous component of the yolk platelets.

Induction of maturation (meiosis) in Xenopus laevis oocytes by three organomercurials.

Three organomercurials, p-hydroxymercuribenzoate, p-hydroxymercuriphenylsulfonate, and mersalyl, induce maturation (meiosis) in a large percentage (20-100 percent) of Xenopus laevis oocytes. Maturation takes place even when the follicle cells which surround the oocytes have been withdrawn. Organomercurial- and progesterone-induced maturations have many features in common: they do not occur when the inducer is injected into the oocytes, they require the presence of Ca++ in the medium, they are inhibited by cycloheximide but not by actinomycin D. In both cases, the maturation producing factor and the pseudomaturation inducing factor are produced. Organomercurial-treated oocytes react normally to activating stimuli; their protein synthesis increases, but uptake of amino acids is strongly inhibited. Progesterone and p-hydroxymercuriphenyl-sulfonate act synergically in inducing maturation. The main difference between the two agents is that p-hydroxymercuriphenylsulfonate must act for several hours, whereas, short contact with progesterone is sufficient to induce maturation.