scholarly journals Two UV-sensitive targets in dorsoanterior specification of frog embryos

Development ◽  
1989 ◽  
Vol 106 (3) ◽  
pp. 511-518 ◽  
Author(s):  
R.P. Elinson ◽  
P. Pasceri
Keyword(s):  
Uv Irradiation ◽  
Normal Development ◽  
Lithium Treatment ◽  
Dorsoventral Polarity ◽  
Prophase I ◽  
Uv Dose ◽  
Metaphase I

Previous work has shown that ultraviolet (UV) irradiation of fertilized frog eggs yields embryos that lack dorsal and anterior structures. The eggs fail to undergo the cortical/cytoplasmic rotation that specifies dorsoventral polarity, and they lack an array of parallel microtubules associated with the rotation. These eggs can be rescued by tilting with respect to gravity, and normal dorsoanterior development occurs. We find here that UV irradiation of Xenopus prophase I oocytes or Rana metaphase I oocytes also causes the dorsoanterior deficient syndrome, but the UV target is different from that in fertilized eggs. Tilting eggs, irradiated as oocytes, with respect to gravity, does not rescue dorsoanterior development, although lithium treatment does. The UV dose required to produce dorsoanterior deficiency for Rana metaphase I oocytes is much less than that for fertilized eggs, and the oocytes can form the array of parallel microtubules and undergo the cortical/cytoplasmic rotation after fertilization. Despite these features of normal development, no dorsoanterior structures form. While the UV target in fertilized eggs is thought to be the parallel microtubules (Elinson & Rowning, 1988; Devl Biol. 128, 185–197), the UV target in the oocytes may be a dorsal determinant.

A gastrulation center in the ascidian egg

Development ◽  
1992 ◽  
Vol 116 (Supplement) ◽  
pp. 53-63 ◽  
Author(s):  
William R. Jeffery
Keyword(s):  
Nervous System ◽  
Uv Irradiation ◽  
Second Phase ◽  
Uv Sensitivity ◽  
Maternal Mrna ◽  
Free Translation ◽  
Vegetal Pole ◽  
Cell Embryo ◽  
Ooplasmic Segregation ◽  
Uv Dose

A gastrulation center is described in ascidian eggs. Extensive cytoplasmic rearrangements occur in ascidian eggs between fertilization and first cleavage. During ooplasmic segregation, a specific cytoskeletal domain (the myoplasm) is translocated first to the vegetal pole (VP) and then to the posterior region of the zygote. A few hours later, gastrulation is initiated by invagination of endoderm cells in the VP region of the 110-cell embryo. After the completion of gastrulation, the embryonic axis is formed, which includes induction of the nervous system, morphogenesis of the larval tail and differentiation of tail muscle cells. Microsurgical deletion or ultraviolet (UV) irradiation of the VP region during the first phase of myoplasmic segregation prevents gastrulation, nervous system induction and tail formation, without affecting muscle cell differentiation. Similar manipulations of unfertilized eggs or uncleaved zygotes after the second phase of segregation have no effect on development, suggesting that a gastrulation center is established by transient localization of myoplasm in the VP region. The function of the gastrulation center was investigated by comparing protein synthesis in normal and UV-irradiated embryos. About 5% of 433 labelled polypeptides detected in 2D gels were affected by UV irradiation. The most prominent protein is a 30 kDa cytoskeletal component (p30), whose synthesis is abolished by UV irradiation. p30 synthesis peaks during gastrulation, is affected by the same UV dose and has the same UV-sensitivity period as gastrulation. However, p30 is not a UV-sensitive target because it is absent during ooplasmic segregation, the UV-sensitivity period. Moreover, the UV target has the absorption maximum of a nucleic acid rather than a protein. Cell-free translation studies indicate that p30 is encoded by a maternal mRNA. UV irradiation inhibits the ability of this transcript to direct p30 synthesis, indicating that p30 mRNA is a UV-sensitive target The gastrulation center may function by sequestration or activation of maternal mRNAs encoding proteins that function during embryogenesis.

Chromosome pairing and potential for intergeneric recombination in some hypotetraploid somatic hybrids of Lycopersicon esculentum (+) Solanum tuberosum

Genome ◽  
1993 ◽  
Vol 36 (6) ◽  
pp. 1032-1041 ◽  
Author(s):  
J. H. de Jong ◽  
A. M. A. Wolters ◽  
J. M. Kok ◽  
H. Verhaar ◽  
J. van Eden
Keyword(s):  
Solanum Tuberosum ◽  
Lycopersicon Esculentum ◽  
Synaptonemal Complex ◽  
Chromosome Pairing ◽  
Somatic Hybrids ◽  
Cytogenetic Study ◽  
Unreduced Gametes ◽  
Root Tip ◽  
Prophase I ◽  
Metaphase I

Three somatic hybrids resulting from protoplast fusions of a diploid kanamycin-resistant line of tomato (Lycopersicon esculentum) and a dihaploid hygromycin-resistant transformant of a monohaploid potato (Solanum tuberosum) line were used for a cytogenetic study on chromosome pairing and meiotic recombination. Chromosome counts in root-tip meristem cells revealed two hypotetraploids with chromosome complements of 2n = 46 and one with 2n = 47. Electron microscope analyses of synaptonemal complex spreads of hypotonically burst protoplasts at mid prophase I showed abundant exchanges of pairing partners in multivalents involving as many as eight chromosomes. In the cells at late pachytene recombination nodules were found in multivalents on both sides of pairing partner exchanges, indicating recombination at both homologous and homoeologous sites. Light microscope observations of pollen mother cells at late diakinesis and metaphase I also revealed multivalents, though their occurrence in low frequencies betrays the reduction of multivalent number and complexity. Precocious separation of half bivalents at metaphase I and lagging of univalents at anaphase I were observed frequently. Bridges, which may result from an apparent inversion loop found in the synaptonemal complexes of a mid prophase I nucleus, were also quite common at anaphase I, though the expected accompanying fragments could be detected in only a few cells. Most striking were the high frequencies of first division restitution in preparations at metaphase II/anaphase II, giving rise to unreduced gametes. In spite of the expected high numbers of balanced haploid and diploid gametes, male fertility, as revealed by pollen staining, was found to be negligible.Key words: synaptonemal complex, recombination, chromosome pairing, somatic hybrid, Lycopersicon esculentum (+) Solanum tuberosum.

The chromosome numbers of five North American and European leech species

1987 ◽  
Vol 65 (3) ◽  
pp. 681-684 ◽  
Author(s):  
Ronald W. Davies ◽  
R. N. Singhal
Keyword(s):  
Chromosome Number ◽  
North American ◽  
Chromosome Numbers ◽  
Chromosome Evolution ◽  
Chromosome Counts ◽  
Prophase I ◽  
Metaphase I

Chromosome counts were obtained for four glossiphoniid species belonging to three genera (Glossiphonia, Theromyzon, Placobdella) and for one erpobdellid species (Dina lineata) of freshwater leeches. Theromyzon rude, which has a Palaearctic distribution, had seven bivalents at prophase I and metaphase I, while the Holarctic T. tessulatum had eight bivalents, giving diploid chromosome numbers of 14 and 16, respectively. Placobdella papillifera from Alberta had a chromosome number of 2n = 24 and Glossiphonia complanata from Alberta and England had chromosome counts of 2n = 28. At prophase I and metaphase I nine bivalents occurred in the majority of the nuclei of Dina lineata. These findings are discussed in relation to the chromosome evolution and phylogenetic schemes proposed by previous authors.

scholarly journals Functional Properties of Borrelia burgdorferi recA

2004 ◽  
Vol 186 (8) ◽  
pp. 2275-2280 ◽  
Author(s):  
Dionysios Liveris ◽  
Vishwaroop Mulay ◽  
Ira Schwartz
Keyword(s):  
Gene Expression ◽  
Borrelia Burgdorferi ◽  
Uv Irradiation ◽  
Reca Protein ◽  
Primary Role ◽  
Rapid Loss ◽  
E Coli ◽  
Uv Dose ◽  
Null Mutants

ABSTRACT Functions of the Borrelia burgdorferi RecA protein were investigated in Escherichia coli recA null mutants. Complementation with B. burgdorferi recA increased survival of E. coli recA mutants by 3 orders of magnitude at a UV dose of 2,000 μJ/cm2. The viability at this UV dose was about 10% that provided by the homologous recA gene. Expression of B. burgdorferi recA resulted in survival of E. coli at levels of mitomycin C that were lethal to noncomplemented hosts. B. burgdorferi RecA was as effective as E. coli RecA in mediating homologous recombination in E. coli. Furthermore, E. coli λ phage lysogens complemented with B. burgdorferi recA produced phage even in the absence of UV irradiation. The level of phage induction was 55-fold higher than the level in cells complemented with the homologous recA gene, suggesting that B. burgdorferi RecA may possess an enhanced coprotease activity. This study indicates that B. burgdorferi RecA mediates the same functions in E. coli as the homologous E. coli protein mediates. However, the rapid loss of viability and the absence of induction in recA expression after UV irradiation in B. burgdorferi suggest that recA is not involved in the repair of UV-induced damage in B. burgdorferi. The primary role of RecA in B. burgdorferi is likely to be a role in some aspect of recombination.

scholarly journals UV-Induced Formation of Ice XI Observed Using an Ultra-High Vacuum Cryogenic Transmission Electron Microscope and its Implications for Planetary Science

2021 ◽  
Vol 9 ◽  
Author(s):  
Akira Kouchi ◽  
Yuki Kimura ◽  
Kensei Kitajima ◽  
Hiroyasu Katsuno ◽  
Hiroshi Hidaka ◽  
...  
Keyword(s):  
Electron Microscope ◽  
Solar System ◽  
Uv Irradiation ◽  
Transmission Electron Microscope ◽  
High Vacuum ◽  
Planetary Science ◽  
Ultra High Vacuum ◽  
Outer Solar System ◽  
Transmission Electron ◽  
Uv Dose

The occurrence of hydrogen atom-ordered form of ice Ih, ice XI, in the outer Solar System has been discussed based on laboratory experiments because its ferroelectricity influences the physical processes in the outer Solar System. However, the formation of ice XI in that region is still unknown due to a lack of formation conditions at temperatures higher than 72 K and the effect of UV-rays on the phase transition from ice I to ice XI. As a result, we observed the UV-irradiation process on ice Ih and ice Ic using a newly developed ultra-high vacuum cryogenic transmission electron microscope. We found that ice Ih transformed to ice XI at temperatures between 75 and 140 K with a relatively small UV dose. Although ice Ic partially transformed to ice XI at 83 K, the rate of transformation was slower than for ice Ih. These findings point to the formation of ice XI at temperatures greater than 72 K via UV irradiation of ice I crystals in the Solar System; icy grains and the surfaces of icy satellites in the Jovian and Saturnian regions.

UV disinfection of wastewater effluents for unrestricted irrigation

2006 ◽  
Vol 54 (3) ◽  
pp. 83-88 ◽  
Author(s):  
A.M. Nasser ◽  
H. Paulman ◽  
O. Sela ◽  
T. Ktaitzer ◽  
H. Cikurel ◽  
...  
Keyword(s):  
Uv Irradiation ◽  
Wastewater Reuse ◽  
High Rate ◽  
Uv Disinfection ◽  
Secondary Effluent ◽  
E Coli ◽  
Uv Dose ◽  
Inactivation Efficiency ◽  
Transmission Of Disease

Wastewater reuse in arid regions is important for the production of a water resource to be utilised for non-potable purposes and to prevent the environmental transmission of disease-causing agents. This study was conducted to evaluate the effect of water quality on the comparative disinfection efficiency of viruses, bacteria and spores by UV irradiation. Furthermore, the microbial quality of effluent produced by coagulation, high rate filtration (HRF) and either UV irradiation or chlorination was determined. Using low pressure collimated beam, a UV dose of 80 mWs/cm2 was needed to achieve a 3-log10 inactivation of either rotavirus SA-11 or coliphage MS2, whereas over 5-log10 inactivation of E. coli was reached with a dose of only 20 mWs/cm2. B. subtilis inactivation was found to be linear up to a dose of 40 mWs/cm2 and then a tailing up to a UV dose of 120 mWs/cm2 was observed. It is worth noting that effluent turbidity of <5 NTU did not influence the inactivation efficiency of UV irradiation. Operation of a pilot plant to treat secondary effluent by coagulation, HRF and UV disinfection at a UV dose of 80 mWs/cm2 resulted in the production of high quality effluent in compliance with the Israel standards for unrestricted irrigation (<10 CFU/100 mL faecal coliform and turbidity of <5 NTU). Sulphite reducing clostridia (SRC) were found to be more resistant than coliphages and F coliform for UV irradiation. The results of this study indicated that UV disinfection is suitable for the production of effluents for unrestricted irrigation of food crops.

scholarly journals SKP1 drives the prophase I to metaphase I transition during male meiosis

2020 ◽  
Vol 6 (13) ◽  
pp. eaaz2129 ◽  
Author(s):  
Yongjuan Guan ◽  
N. Adrian Leu ◽  
Jun Ma ◽  
Lukáš Chmátal ◽  
Gordon Ruthel ◽  
...  
Keyword(s):  
Okadaic Acid ◽  
Meiotic Prophase ◽  
Essential Role ◽  
Male Meiosis ◽  
Prophase I ◽  
Ubiquitin E3 Ligase ◽  
Competence Factor ◽  
Competence Acquisition ◽  
Mi Transition ◽  
Metaphase I

The meiotic prophase I to metaphase I (PI/MI) transition requires chromosome desynapsis and metaphase competence acquisition. However, control of these major meiotic events is poorly understood. Here, we identify an essential role for SKP1, a core subunit of the SKP1–Cullin–F-box (SCF) ubiquitin E3 ligase, in the PI/MI transition. SKP1 localizes to synapsed chromosome axes and evicts HORMAD proteins from these regions in meiotic spermatocytes. SKP1-deficient spermatocytes display premature desynapsis, precocious pachytene exit, loss of PLK1 and BUB1 at centromeres, but persistence of HORMAD, γH2AX, RPA2, and MLH1 in diplonema. Strikingly, SKP1-deficient spermatocytes show sharply reduced MPF activity and fail to enter MI despite treatment with okadaic acid. SKP1-deficient oocytes exhibit desynapsis, chromosome misalignment, and progressive postnatal loss. Therefore, SKP1 maintains synapsis in meiosis of both sexes. Furthermore, our results support a model where SKP1 functions as the long-sought intrinsic metaphase competence factor to orchestrate MI entry during male meiosis.

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