Dimethylformamide-induced changes in the radiation survival of low- and high-passage intestinal epithelial cells (IEC-17) in vitro

The effects of dimethylformamide (DMF) on the radiation response of low- and high-passage intestinal epithelial cells (IEC-17) were examined. The IEC-17 cell line, a rat intestinal epithelial cell line, exhibited a bimodal response to X radiation. The sensitive fraction, which was attributed to a stem cell-like component, had a D0 of 0.90 Gy. The resistant fraction, thought to be the expression of a more mature component, exhibited a D0 of 2.00 Gy. Treatment using a putative cell differentiating agent, N,N-dimethylformamide, increased the resistant fraction of the population from 35 to 80%, suggesting that DMF treatment (100 mM) increased the proportion of mature cells in the IEC-17 cell population. In addition, extended age in culture (greater than 100 passages) resulted in altered morphology, decreased doubling time, increased chromosome number, and loss of anchorage dependence, all features characterizing spontaneously transformed high-passage IEC-17 cells. These high-passage cells also exhibited a bimodal response to X radiation; the sensitive fraction had a D0 of 0.80 Gy while the resistant fraction D0 was 1.50 Gy. DMF increased the resistant fraction from 35 to 55% of the population. Results suggested that the different radiosensitivities of the subpopulations remained throughout the spontaneous transformation of high-passage IEC-17 cells.     

Craniofacial ontogeny in centrosaurine dinosaurs (Ornithischia: Geratopsidae): taxonomic and behavioral implications

Centrosaurine ceratopsians are characterized by well developed nasal horncores or bosses, relatively abbreviated supraorbital horncores or bosses, and adorned parietosquamosal frills. Recent study of several paucispecific (low diversity) bonebed assemblages in Alberta and Montana has contributed greatly to our understanding of ontogenetic and taxonomic variation in the skulls of centrosaurines. Relative age determination of centrosaurines is now possible through examination of ontogenetic change in several characters, including the surface bone morphology of specific skeletal elements. The within-group taxonomy of centrosaurines is based almost entirely on characters of the skull roof, relating particularly to horns and frills. Juvenile and sub-adult centrosaurines are characterized by relatively simple, unadorned skulls compared to their adult counterparts. As in numerous living taxa, the cranial ornaments of centrosaurines developed late in ontogeny, as individuals approached or attained adult size. An important implication arising directly from this study is that juvenile and sub-adult centrosaurines are difficult to distinguish taxonomically at the specific level. Two monospecific genera represented only by immature materials, Brachyceratops montanensis and Monoclonius crassus , cannot be defended and should be considered nomina dubia . The late ontogenetic development and diverse taxonomic variation of horn and frill morphologies support the contention diat these structures are best interpreted as reproductive characters employed in mate competition.     

Diploicia africana comb. nov. (lichenized Ascomycetes, Physciaceae), an endemic species from the Cape Province (South Africa)

The saxicolous lichenized ascomycete Diploicia africana comb. nov. (Physciaceae) is endemic in the Cape Floral Kingdom (South Africa). Its taxonomy, morphology, chemistry, biogeography, and ecology is discussed. The most important characters of the genus Diploicia and the better known species of the genus are outlined.     

The wrong way to think about gene conversion?

Summary The sex circle model for crossing over and gene conversion proposed by Stahl has a number of properties which are in conflict with a considerable body of recombination data in fungi. The model is unable to explain the observed frequencies of gene conversion and postmeiotic segregation for particular mutants in several species. It does not provide an explanation for fine structure map expansion, nor does it account satisfactorily for the polarised distribution of outside markers amongst allelic recombinants.