Cytological mechanisms of gynogenesis and sperm incorporation in unreduced diploid eggs of the clonal loach, Misgurnus anguillicaudatus (Teleostei: Cobitidae)

The loach Misgurnus anguillicaudatus comprises diploid clonal, triploid and diploid-triploid mosaic individuals in a wild population on Hokkaido island, Japan. When diploid eggs of clonal loaches are fertilized by haploid sperm of normal bisexual loaches, both diploid clonal and non-diploid aclonal individuals occur in the progeny. Flow cytometry and microsatellite analyses revealed that the occurrence of triploid, diploid-triploid and other progeny was essentially due to the genetic incorporation of sperm to diploid clonal genomes of unreduced eggs. In this study, we examined the influence of water temperature from fertilization to early embryogenesis on frequencies of diploid clonal and other progeny and observed that progeny of three out of four clonal females examined exhibited approximately constant rates of diploid clonal individuals (54.2-68.9%) at hatching stage. Thus, no drastic increase of non-diploid progeny was detected. However, the 28 degrees C group of the fourth clonal female gave significantly lower rate (28.1%) of diploid clonal progeny, suggesting that this temperature might be a critical or a borderline temperature inducing sperm incorporation. We also examined the cytological process by which diploid clonal and other aclonal progeny develop after fertilization. In some fertilized eggs, the sperm nucleus remained condensed throughout fertilization and early embryogenesis and never fused with the female pronucleus. This cytological observation concludes that clonal eggs develop by the mechanism of gynogenesis. However, some other eggs showed the cytological process of syngamy between the female pronucleus and an accidentally formed male nucleus, suggesting the formation of triploid progeny. The syngamy between an accidentally activated sperm nucleus with a male pronucleus-like structure and nucleus of a blastomere of gynogenetically developing clonal diploid embryo might produce a diploid-triploid mosaic individual.     

Occurrence of aneuploidy in radiation gynogenesis of carp, Cyprinus carpio L.

DNA content and chromosome numbers were studied in gynogenetic and normal carp embryos. Gynogenetic embryos showed the haploid chromosome number; the occurrence of spontaneous diploidization was rare. Early cold shock treatment of the gynogenetic zygotes resulted in the retention of the second polar body producing a much higher proportion of normally developing viable larvae. The appearance of large numbers of aneuploid embryos in the cold-treated gynogenetic group is explained by the loss or breakdown of chromosomes that are caused in their turn by the absorbtion of the second polar body through the cold treatment.     

Immunocorrective action of tuftsin during exposure to ionizing radiation

The effect of the tetrapeptide tuftcin (Thr-Lys-Pro-Arg) on the humoral immune response in CBA mice exposed to sublethal irradiation in a dose of 450 sGy was studied. The drug was injected intraperitoneally for 5 days before (series I) or after (series II) radiation exposure. It has been shown that taftcin has no protective action but decreases considerably the immune response lowering due to radiation.     

Abiogenic synthesis of oligonucleotides on kaolinite under the action of ultraviolet radiation

Summary The present work deals with the processes involved in the abiogenic polycondensation of nucleotides adsorbed on the clay mineral kaolinite under the action of ultraviolet (UV) radiation. The dependence of the yield of synthesis products on irradiation dose was studied. The maximum yield corresponds to a 6-h exposure. The newly synthesized substances were analyzed by ion-exchange chromatography. Some fractions were studied for the type of bonds they contained by venom phosphodiesterase and RNase T₂ enzymatic hydrolysis. It was determined that some of the products synthesized by exposure of AMP adsorbed on the surface of clay particles to UV radiation may be looked upon as oligonucleotides in which some fragments have 2–5-bonded and others 3–5-bonded nucleotides     

Analysis of shivering in nonperiheral cooling during pyrogen fever

The shivering reaction to nonperipheral cooling was monitored in goats. No difference in reaction between normothermic and fevered animals was found. It is concluded that fever is not caused by a change of gain in thermosensors.     

Changes in mitochondria density during oogenesis of loach]

The growth of loach oocytes is accompanied by an increase in the density of mitochondria. Simultaneously with the increase in density an acceleration of 14C-valine incorporation into mitochondrial proteins takes place. It is assumed that the increase in mitochondria density during oogenesis is due to an increase in the amount of membrane material per unit of mitochondria weight.     

Helicase action of dnaB protein during replication from the Escherichia coli chromosomal origin in vitro

Initiation of bidirectional replication from the origin of the Escherichia coli chromosome (oriC) proceeds through stages in which the components of the two replication forks are assembled. From a complex containing proteins dnaA, dnaB, and dnaC bound at oriC, the dnaB helicase moves in both directions to unwind the duplex. In the absence of replication, this unwinding generates a bubble at oriC coated by single strand binding protein. Addition of gyrase allows unwinding to proceed extensively in both directions from oriC at 60 base pairs/s/fork at 37 degrees C. This rate is sharply dependent on temperature and also stimulated by both primase and DNA polymerase III holoenzyme, even in the absence of DNA synthesis. Primer and DNA synthesis are efficient when coupled to template unwinding. DNA synthesis proceeds bidirectionally from oriC at a rate limited by unwinding. With extensive unwinding preceding DNA synthesis, initiations are not limited to oriC.     

Activation of mitochondrial DNA synthesis during loach embryogenesis

Mitochondria isolated from unfertilized loach (Misgurnus fossilis) eggs incorporate 3H-dTTP at a low rate (0,01 pmoles 3H-dTTP-mg of mitochondrial protein/1 hr incubation). After fertilization the rate of 3H-dTTP incorporation into DNA of mitochondria isolated from embryos of different developmental stages increases exponentially, doubling each 7 hours, and attains the maximum to 35 hour of development. This stage corresponds to the beginning of movement. DNA synthesis in mitochondria from unfertilized eggs resembles repair; as early as 6 hours after fertilization the labeling pattern of mt-DNA is of replicative type. This replicative type of labeling is observed throughout all early development. Activation of mt-DNA biosynthesis in the course of early development is not accompanied by any changes of DNA polymerase activity in mitochondrial extracts or in mitochondrial lysates.     

Features of the ultrastructure of loach embryos under the influence of norfloxacin

Results from a study of the ultrastructure of embryos of loach, Misgurnus fossilis L., on the stages of the first and tenth blastomere division under the control and in the presence of the fluoroquinolone series antibiotic norfloxacin (5 and 25 μg/ml) in the incubation medium are presented. The action of norfloxacin leads to ultrastructural changes in the cell organelles, such as hypertrophy of the rough and smooth endoplasmic reticulum and disorganization of the mitochondria and the plasma membranes of the embryos. It is established that fluoroquinolone inhibits biosynthesis processes that directly influence the biosynthesis structure of the blastomeres. Destructive changes in the organelles are a consequence of disturbances in assimilation processes that ultimately lead to death of the embryos. Thus, the results that have been obtained indicate that high embryotoxicity is characteristic of norfloxacin.