INTERRELATIONSHIPS BETWEEN POLYAMINES AND NUCLEIC ACIDS. CHANGES OF POLYAMINE AND NUCLEIC ACID CONCENTRATIONS IN THE GROWING FISH BRAIN (SALMO IRIDEUS GIBB.)

Abstract— In contrast to mouse brain, the content of putrescine in fish brain considerably exceeds that of spermine and spermidine. While we observed constant protein, RNA and spermidine concentrations in fish brains of weights between 60 and 800 mg, DNA and spermine concentrations diminished with increasing brain weight, the content of spermine per cell being constant throughout life. It can be concluded from our results that growth of fish brain results both from cell enlargement and cell proliferation. The concomitant changes of spermine and DNA concentrations in the growing fish brain are the first example of a direct quantitative relationship between these cell constituents and provides evidence on their possible functional relationship in the cell nucleus.     

Mysterious bio-duck sound attributed to the Antarctic minke whale (Balaenoptera bonaerensis)

For decades, the bio-duck sound has been recorded in the Southern Ocean, but the animal producing it has remained a mystery. Heard mainly during austral winter in the Southern Ocean, this ubiquitous sound has been recorded in Antarctic waters and contemporaneously off the Australian west coast. Here, we present conclusive evidence that the bio-duck sound is produced by Antarctic minke whales (Balaenoptera bonaerensis). We analysed data from multi-sensor acoustic recording tags that included intense bio-duck sounds as well as singular downsweeps that have previously been attributed to this species. This finding allows the interpretation of a wealth of long-term acoustic recordings for this previously acoustically concealed species, which will improve our understanding of the distribution, abundance and behaviour of Antarctic minke whales. This is critical information for a species that inhabits a difficult to access sea-ice environment that is changing rapidly in some regions and has been the subject of contentious lethal sampling efforts and ongoing international legal action.     

A DNA Damage Checkpoint Pathway Coordinates the Division of Dikaryotic Cells in the Ink Cap Mushroom Coprinopsis cinerea

The fungal fruiting body or mushroom is a multicellular structure essential for sexual reproduction. It is composed of dikaryotic cells that contain one haploid nucleus from each mating partner sharing the same cytoplasm without undergoing nuclear fusion. In the mushroom, the pileus bears the hymenium, a layer of cells that includes the specialized basidia in which nuclear fusion, meiosis, and sporulation occur. Coprinopsis cinerea is a well-known model fungus used to study developmental processes associated with the formation of the fruiting body. Here we describe that knocking down the expression of Atr1 and Chk1, two kinases shown to be involved in the response to DNA damage in a number of eukaryotic organisms, dramatically impairs the ability to develop fruiting bodies in C. cinerea, as well as other developmental decisions such as sclerotia formation. These developmental defects correlated with the impairment in silenced strains to sustain an appropriated dikaryotic cell cycle. Dikaryotic cells in which chk1 or atr1 genes were silenced displayed a higher level of asynchronous mitosis and as a consequence aberrant cells carrying an unbalanced dose of nuclei. Since fruiting body initiation is dependent on the balanced mating-type regulator doses present in the dikaryon, we believe that the observed developmental defects were a consequence of the impaired cell cycle in the dikaryon. Our results suggest a connection between the DNA damage response cascade, cell cycle regulation, and developmental processes in this fungus.     

Mechanism of systemic immune suppression by UV irradiation in vivo. II. The UV effects on number and morphology of epidermal Langerhans cells and the UV-induced suppression of contact hypersensitivity have different wavelength dependencies

We previously reported that broad band UV radiation or narrow bands of UV (Hbw 3 nm) of wavelengths 250 to 320 nm cause a systemic suppression of contact hypersensitivity (CHS) in mice, observed when the contact sensitizer is applied to a nonirradiated site. To determine if this effect is associated with UV-induced alterations in epidermal Langerhans cell (LC) numbers and morphology, we performed the following study. LC were identified by ATPase staining of EDTA-separated epidermal sheets. Electron microscope studies confirmed that this method was a satisfactory indicator of the presence of LC; we found no evidence for LC which did not stain for ATPase in either irradiated or unirradiated epidermis. Mice were irradiated on the back with narrow band UV of peak wavelength 270, 290, or 320 nm. The irradiated skin was excised 24 hr later and was stained as described. The number of LC with ATPase staining dendrites and the number of nondendritic LC were enumerated. We found that UV radiation of 270 or 290 nm caused 1) an alteration in LC morphology (loss of dendrites) and 2) a decrease in the total number of epidermal LC. Both effects occurred in a dose-dependent fashion. Previously, these same wavelengths of narrow band UV, but at higher doses, had been shown to cause systemic suppression of CHS. In this study, the doses of 270 or 290 nm UV that resulted in the decreased LC numbers and alterations in LC morphology described above were insufficient to cause systemic suppression of CHS. The converse was found if the irradiating waveband of UV had a peak at 320 nm. A dose of 320 nm UV that caused 50% systemic suppression of CHS had no effect on either the number or the morphology of LC at the site of irradiation. In addition, the number and morphology of LC were unaffected in the ventral epidermis (site of contact sensitization) of mice that had been previously irradiated on the back with a systemically suppressive dose of UV. We conclude: (a) UV-induced alterations in the number and morphology of LC at the site of irradiation are not necessary for the generation of systemic suppression of CHS by UV radiation; this indicates that the initial UV-absorbing event triggering systemic suppression is neither a loss of, nor morphologic alterations to, LC at the irradiation site. (b) A systemic effect of UV radiation on the number and morphology of LC at the unirradiated site of contact sensitization does not occur, and thus is not responsible for the UV-induced systemic suppression of CHS by UV radiation.