Asymmetric cell division and differentiation; fern spore germination as a model. I. Physiological aspects

1985 ◽  
Vol 86 ◽  
pp. 213-226
Author(s):  
John H. Miller
Keyword(s):  
Cell Division ◽  
Spore Germination ◽  
Metal Binding ◽  
Asymmetric Cell Division ◽  
Red Light ◽  
Metal Binding Sites ◽  
Sequence Of Events ◽  
Cytoplasmic Microtubules ◽  
External Stimuli ◽  
The Relationship

SynopsisDuring germination of Onoclea sensibilis spores, the spore nucleus moves from a central location to one end. Cell division partitions the spore into a small cell which differentiates into a rhizoid, and a larger cell which gives rise, by continued division, to the prothallus. Spore germination is a valuable system in which to study the relationship between asymmetric cell division and the initiation of cell differentiation. It appears that cytoplasmic microtubules and some lipophilic site in the spore are both involved in premitotic nuclear migration. Asymmetric cell division is an obligate step in the initiation of rhizoid differentiation. One hypothesis is that the nucleus must be confined to a small, localised region of the spore for a sufficient time before differentiation can occur, and the confinement is accomplished by the asymmetric cell division. Metal-binding sites are present in the spore coat, specifically on the proximal face. Several types of evidence suggest that the metal-binding region is involved in spore polarity. The sequence of events during germination appears to involve both polarity which is inherent in the spore and polarity which may be imposed by external stimuli. Experiments in which spores are treated with colchicine and polarised red light reveal both types of polarity.

Asymmetric cell division and differentiation; fern spore germination as a model. II. Ultrastructural studies

1985 ◽  
Vol 86 ◽  
pp. 227-230
Author(s):  
Alix R. Bassel
Keyword(s):  
Cell Division ◽  
Metal Binding ◽  
Asymmetric Cell Division ◽  
Red Light ◽  
Nuclear Migration ◽  
Silver Stain ◽  
Metal Binding Sites ◽  
Ultrastructural Studies ◽  
Fern Spore Germination

SynopsisThe germination of Onoclea spores is a model system with many advantages for the study of asymmetric cell division and cellular differentiation. Our results suggest that both microtubules and a lipophilic site are important in the nuclear migration to one end of the spore prior to asymmetric cell division. A metalbinding region containing pore-like structures in the proximal face of the spore coat may be a source of the inherent polarity of the spore. The pattern of endogenous metal binding during germination has been characterised using a sulphide-silver stain. Metal-binding sites are described in a differentiating system in which polarity is imposed externally using polarised red light. The possibility of a role of ion gradients in determining the direction of nuclear migration is discussed.

Nitrogen- and sulfur-containing models for metallo-enzymes. Part I. Synthesis and physical studies of 2(2-pyridyl)-1,3-dithioalkyl-2-propanols, 2(2-pyridyl)- and 2(2-imidazolyl)-1,3-dimercapto-2-propanols

1981 ◽  
Vol 59 (1) ◽  
pp. 65-75 ◽  
Author(s):  
N. J. Curtis ◽  
R. S. Brown
Keyword(s):  
Small Molecule ◽  
Metal Binding ◽  
Binding Sites ◽  
Divalent Metals ◽  
Metal Binding Sites ◽  
Ph Values ◽  
Biochemical Systems ◽  
Relationship Of ◽  
The Relationship ◽  
Sulfur Containing

Several compounds of the title class have been synthesized as small-molecule analogues for the metal-binding sites in such biochemical systems as ADH. The ligands containing pyridine and two thioethers do not bind divalent metals (Co2+, Zn2+, Cu2+, Ni2+), strongly suggesting that thioethers are poorly chelated. However, the analogues containing free SH groups bind divalent metals very strongly, producing complexes with limited solubility at pH values in excess of 6. Titration of the latter ligands in the presence of 1 equiv. Zn2+ indicates the consumption of 3 equiv. OH− by pH 6, one for the [Formula: see text] ionization, and one for each S—H bound to Zn2+. On the basis of these data the resulting complexes are considered to neutral bis-thiolates. The relationship of these data to the state of ionization of the Zn2+-cysteine SH's in ADH is discussed.

Centromere assembly and non-random sister chromatid segregation in stem cells

2020 ◽  
Vol 64 (2) ◽  
pp. 223-232 ◽  
Author(s):  
Ben L. Carty ◽  
Elaine M. Dunleavy
Keyword(s):  
Stem Cells ◽  
Cell Division ◽  
Cell Fate ◽  
Sister Chromatid ◽  
Asymmetric Cell Division ◽  
Protein A ◽  
Germline Stem Cells ◽  
Sister Chromatids ◽  
Centromere Protein A ◽  
Oocyte Meiosis

Abstract Asymmetric cell division (ACD) produces daughter cells with separate distinct cell fates and is critical for the development and regulation of multicellular organisms. Epigenetic mechanisms are key players in cell fate determination. Centromeres, epigenetically specified loci defined by the presence of the histone H3-variant, centromere protein A (CENP-A), are essential for chromosome segregation at cell division. ACDs in stem cells and in oocyte meiosis have been proposed to be reliant on centromere integrity for the regulation of the non-random segregation of chromosomes. It has recently been shown that CENP-A is asymmetrically distributed between the centromeres of sister chromatids in male and female Drosophila germline stem cells (GSCs), with more CENP-A on sister chromatids to be segregated to the GSC. This imbalance in centromere strength correlates with the temporal and asymmetric assembly of the mitotic spindle and potentially orientates the cell to allow for biased sister chromatid retention in stem cells. In this essay, we discuss the recent evidence for asymmetric sister centromeres in stem cells. Thereafter, we discuss mechanistic avenues to establish this sister centromere asymmetry and how it ultimately might influence cell fate.

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