Primordial cell

Do these prokaryotic organisms display a primitive iron metabolism, in the sense that they form a relatively limited number of iron compounds, and are they accordingly good candidates to suspect as direct descendants of the primordial cell ... 

Jay, D. and Gilbert, W. (1987). Basic protein enhances the encapsulation of DNA into lipid vesicles model for the formation of primordial cells. Proc. Natl. Acad. Sci. 

J. R. Merriam, Estimating primordial cell numbers in Drosophila imaginal discs and histoblasts. In Genetic Mosaics and Cell Differentiation, W. Gehring, ed., Springer-Verlag, New York, 1978, pp. 71-96. 

Hyaluronan is prominent in the very earliest stage of embryogenesis, in maintenance of the undifferentiated state, with its removal required prior to the onset of differentiation.85 The presence of HA inhibits the process of differentiation, permitting expansion of primordial cell masses. In organotypic cultures of rat keratinocytes, HA suppresses epidermal differentiation,86 must be removed before the program of differentiation can be initiated. 

Despite their immense diversity of sizes, shapes, and capacities, living cells are also remarkably similar. In fact, all modem cells are believed to have evolved from primordial cells over three billion years ago (see Special Interest Box 2.2). The common features of prokaryotic and eukaryotic cells include their similar chemical composition and the universal use of DNA as genetic material. The objective of this chapter is to provide an overview of cell structure. This review is a valuable exercise because biochemical reactions do not occur in isolation. It is becoming increasingly obvious that our understanding of living processes is incomplete without knowledge of their cellular context. After a brief discussion of some basic themes in cellular structure and function, the essential structural features of prokaryotic and eukaryotic cells will be described in relation to their biochemical roles. 

Comment. In the primordial cells, and in the early multicellular eukaryotes, the RNA/DNA complex raled the intron-rich primordial cells (LECA/LUCA of Csuros et al). In multicellular eukaryotes, the single stem cells retain the ancient mler, the RNA/DNA complex. So are the zygote-derived early embryonic cells. The dominant somatic cell mass in the advanced multicellular hosts is under the strict rule of a DNA/RNA complex. Once transformed, in these cells the RNA/DNA complex regains its primordial vitality manifested by the expression of introns and their derivative multiple RNAs. The presumably intron-rich transformed cell re-gained the immortality, independence and persistence endowed to the original unicellular eukaryotes, which survived the most severe conflicts in the environment of the... 

Comment. It must have been the adaptability of the genomes of the survivors, due to pre-inserted SINE and other retrotransposons, in the post-cataclysmic environment, that supported the newer generations, while the lack of these faculties doomed the prior inhabitants, which flourished in a different antecedent environment. The power of the RNA/DNA complex once installed in the primordial cells is to generate just about any biological change either in advance (but without precise foresight), or in response to demand, and remain just about inexhaustible. 

Comment. It was a response to physico-chemical inducers,that the ancient cells managed to survive by activating their cell survival pathways. Antiviral self-defense mechanisms were installed. In the end, the descendants of the single cells, and their viruses both remain in existence, forming the largest biomass on Earth. The primordial cell survival pathways remained conserved in the form of much more elaborate, and interrelated sequences In the stem and somatic cells of multicellular hosts. In addition to physico-chemical inducers, it is an armada of biological agents... 

Nesbitt and Gartler (1971) have shown that female mice heterozygous for Cattanach s translocation (Cattanach, 1962) have an inactive normal X chromosome which can be distinguished from cells containing an inactive translocated X chromosome. They interpreted their results to mean that X chromosome activation occurs around the time of implantation but before the determination of the primordial cell pools for the various tissues, within the inner cell embryonic mass. Comparisons of allophenic and X inactivation mosaic mice indicate a tendency for a coherent clonal growth of the inner ceU mass in the development of the mammalian blastocyst (Nesbitt and Gattler, 1971). 

Metcalfe, W. (1985) Sensory neuronal growth cones comigrate with posterior lateral line primordial cells in the zebrafish. J. Comp Neurol. 238,218-224. 

Chalonas antitemplate substances tissue-spedfic, endogenous mitosis inhibitors. C. are allegedly produced by mature or differentiated cells, and it is claimed that they irrhibit division of primordial cells by a type of negative feedback. The effect of C. is re-verdble and not spedes-spedfic. Urey have been iso-... 

The corresponding mutations are not expressed phenotypically in the primordial cells in individuals with the position effect of the mosaic type ... 

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