Morphological variation in intergrade pupfish populations from the Pecos River, Texas, U.S.A.

In the early 1980s, sheepshead minnow Cyprinodon variegates was introduced into the Pecos River, Texas, U.S.A. where it hybridized with the endemic Pecos pupfish C. pecosensis . By 1985, pupfish populations throughout approximately 300 km of the river consisted exclusively of individuals of hybrid origin (intergrades). There was significant ( P <0·05) geographic variation in most morphological characters; the general pattern of variation was of a bidirectional cline centred near Pecos, Texas. At that site, morphology of intergrade populations resembled mostly that of the introduced species. Upstream and downstream from Pecos, morphology shifted progressively toward that typical of the native form. Intergrade populations were morphologically intermediate to the parental forms, showed a rapid approach to random assortment of characters, and generally exhibited greater morphological variability than occurred in either parent species. These observations and the consistent lack of bimodality in frequency distributions of a morphological hybrid index support the contention that intergrade populations comprise panmictic admixtures of C. variegates and C. pecosensis .     

The effects of cervical dilation on plasma PGFM, progesterone and the duration of luteal function in diestrous mares

Transcervical diagnostic techniques may alter the length of the equine estrous cycle and affect subsequent luteal function. Therefore, nine mares were used to determine the effect of cervical dilation on plasma 13, 14-dihydro, 15-keto-prostaglandin F(2) (PGFM), progesterone (P(4)) and posttreatment duration of luteal function. Mares were given a daily score of 0 to 4 based on sexual receptivity. Five days following the end of receptivity, mares were randomly assigned to one of three, 3 x 3 latin squares. Control mares received no cervical dilation. Cervically stimulated mares recieved cervical dilation for 60 sec. Cervically stimulated plus inhibitor mares were dilated similarly to cervically stimulated mares, but received a prostaglandin synthetase inhibitor 30 min prior to treatment. Each mare completed all three treatments in three consecutive estrous cycles. Plasma PGFM and P(4) were determined by RIA. Plasma PGFM was lower (P<0.05) in cervically stimulated plus inhibitor than control and cervically stimulated mares. In addition, plasma P(4) was lower (P<0.10) in cervically stimulated plus inhibitor than in control and cervically stimulated mares. Luteal function following treatments did not differ. These data indicate that neither plasma PGFM and P(4) nor the duration of luteal function were affected by cervical dilation. However, administration of a prostaglandin synthetase inhibitor prior to cervical dilation decreased plasma PGFM and P(4) concentrations.     

Identification of a conserved sequence in the non-coding regions of many human genes.

We have analyzed a sequence of approximately 70 base pairs (bp) that shows a high degree of similarity to sequences present in the non-coding regions of a number of human and other mammalian genes. The sequence was discovered in a fragment of human genomic DNA adjacent to an integrated hepatitis B virus genome in cells derived from human hepatocellular carcinoma tissue. When one of the viral flanking sequences was compared to nucleotide sequences in GenBank, more than thirty human genes were identified that contained a similar sequence in their non-coding regions. The sequence element was usually found once or twice in a gene, either in an intron or in the 5' or 3' flanking regions. It did not share any similarities with known short interspersed nucleotide elements (SINEs) or presently known gene regulatory elements. This element was highly conserved at the same position within the corresponding human and mouse genes for myoglobin and N-myc, indicating evolutionary conservation and possible functional importance. Preliminary DNase I footprinting data suggested that the element or its adjacent sequences may bind nuclear factors to generate specific DNase I hypersensitive sites. The size, structure, and evolutionary conservation of this sequence indicates that it is distinct from other types of short interspersed repetitive elements. It is possible that the element may have a cis-acting functional role in the genome.     

Molecular orbital studies of oxygen activation and mechanisms of cytochromes P-450-mediated oxidative metabolism of xenobiotics

Molecular dimensions and molecular orbital calculations of the electronic structures of 56 substrates, inhibitors and inducers of the cytochromes P-448 and other families of the cytochromes P-450 are reported. Substrates of the cytochromes P-448 are shown to be planar molecules with relatively large values of area/depth², and to have electronic structures with relatively low values for ΔE, the difference in energy between the frontier orbitals (E(LEMO) − E(HOMO)). Substrates of other families of the cytochromes P-450 are globular molecules, with relatively low values of area/depth² and relatively high values of ΔE. Molecular orbital calculations of the active oxygen species, singlet oxygen and superoxy anion, have also been made. Singlet oxygen is a poor electron donor (low values of E(HOMO)) but a good electron acceptor (low values of E(LEMO)), whereas superoxy anion is a good electron donor and a poor electron acceptor. Cytochrome P-448 substrates, which are good electron donors, would preferentially accept singlet oxygen, a good electron acceptor; substrates of the other families of cytochrome P-450, which are less effective electron donors, would preferentially accept superoxy anion, a good electron donor, although substrates of both cytochromes P-448 and other P-450s may accept both species of active oxygen. Together with recent published evidence, these data provide a greater understanding of the mode of activation of oxygen by the various families of the cytochromes P-450, and to the insertion of active oxygen into the substrates. Mechanisms are proposed for the oxygenation of substrates, namely, epoxidation involving singlet oxygen and hydroxylation by superoxy anion. Finally, a detailed explanation of the cytochrome P-450 cycle is discussed, and mechanisms of the different types of oxidative metabolism are presented.     

Transferrin receptor activity in rat mammary epithelial cells

The binding of 125I-transferrin to rat mammary cells isolated by collagenase and hyaluronidase digestion has been investigated. Surface binding was determined at 4 degrees C and total binding also at 4 degrees C but in the presence of 0.1% w/v saponin. KD values between 20 and 25 nM were obtained. Binding assays at 37 degrees C showed the internalisation of the receptor and the bound transferrin was occurring but also provided evidence for an impaired recycling of the receptors to the cell surface in the freshly isolated cells. No differences in total binding were observed in cells prepared at different stages of lactation with a mean value of 29 fmol transferrin bound/micrograms cellular DNA, equivalent to 180,000 receptors per cell.