Evolution of Alu repeats: dynamics of distribution in genome

A mathematical model of evolutionary dynamics of Alu repeats' number in the human genome has been worked out. The model permitted us to observe the dynamics of propagation of Alu repeats within the genome and to evaluate such important parameters of the process mentioned as the rates of transposition (insertion of new copies into the genome) and excision of repeats. The peculiarities of the control of Alu repeats' number in the genome have been discussed, based on the data obtained.     

Redescription of Diaphanosoma celebensis Stingelin, 1900 (Crustacea,Cladocera)

A rare species, Diaphanosoma celebensis (Stingelin, 1900) is redescribed from type material and material from the South of Vietnam. In comparative morphological aspect it is close to D. volzi, but it is relatively less specialized. D. celebensis is known from single locations in Indonesia, Sri Lanka, Vietnam. It probably also occurs in Malaysia. The size frequency and sex structure of a population from Vietnam is described.     

Performance profiles of topical antimicrobials in vitro

The in-vitro efficacy of commercially available topical antimicrobial products against control strains and those from clinical material are compared with an agar diffusion model. The MICs of the constituent antimicrobial compounds have been determined for the same organisms. Plotting the inhibition zone diameters produced by the topical products against the log10 MICs of their constituent antimicrobial compound(s) gives overall product performance profiles for a range of organisms. These profiles confirm that the formulation of a topical product clearly modifies the response obtained with a specific antimicrobial compound.     

Conformations of deoxydinucleoside phosphates containing pyrimidine-pyrimidine photodimers

Conformational analysis of deoxydinucleoside monophosphates with the sequences TpT and CpC have been carried out with the incorporation of both cyclobutane type pyrimidine dimers and 6-4 photoadducts using the methods of molecular mechanics energy minimization. The effect of flexibility with respect to sugar geometries and glycosidic torsions have been studied and the relative energies of a large variety of structures have been compared. The salient features obtained from these calculations have been compared with the crystallographic and spectroscopic data on pyrimidine dimer incorporated deoxydinucleoside monophosphates. Effects of "inserting" the energetically favourable conformations of such structures into B-DNA helices have been discussed in terms of the distortions in helical structures.     

Mathematical model of the simple cells in the visual cortex

A mathematical model for the spatial computations performed by simple cells in the mammalian visual cortex is derived. The construction uses as organizing principles the experimentally observed simple cell linearity and rotational symmetry breaking, together with the constraint that simple cell inputs must effectively be ganglion cell outputs. This leads to a closed form expression for the simple cellkernel in terms of Jacobi-functions. Using a-function identity, it is also shown how Gabor sampling arises as an approximation to this exact kernel for most cells. In addition, the model provides a natural mechanism for introducing the type of nonlinearity observed in some simple cells. The cell's responses to a variety of visual stimuli are calculated using the exact kernel and compared to single cell recordings. In all cases, the model's predictions are in agreement with available experimental data.Work supported by the National Science Foundation, grant PHYS86-20266Work supported by the Department of Energy, contract DE-AC02-76ERO2220     

Astrocyte death in organotypic cultures of fetal spinal cord from rats with unilateral micromelia

Growth and differentiation of neurons and glia in spinal cord explants of 16 days old rat fetuses with teratogen-induced left-sided micromelia were studied. Progressive destruction of astrocytes that differentiate in interstitial zone of cultures was observed in 37% of explants of the left side, while the development was normal in cultures of the right side. Possible mechanisms leading to destruction of astrocytes in cultures of spinal cord regions that innervate anomalous limbs are discussed.     

The transformation of the mammalian genome and the teratogenic activity of chloridin

Susceptibility to the effect of teratogen chloridine of three generations produced from transgenic rats with human growth hormone gene was investigated. The offsprings were shown to reveal elevated teratogenic injury as compared with intact animals.     

Dynamic changes in optic fiber terminal arbors lead to retinotopic map formation: an in vivo confocal microscopic study

Dynamic remodeling of retinal ganglion cell terminal arbors has been proposed to contribute to formation of the topographically ordered retinotectal projection. To test this directly, the growth of individual terminal arbors was observed in live X. laevis tadpoles using a confocal microscope to visualize their complex three-dimensional structure. During initial development, nasal and temporal retinal arbors covered overlapping tectal areas. Despite subsequent remodeling, the dimensions and positions of the temporal arbors remained relatively stable. In contrast, the nasal arbors grew caudally, as they extended caudal branches and retracted rostral branches. These results suggest that differences in the remodeling of the nasal and temporal arbors lead to the emergence of retino-topography along the rostrocaudal axis of the tectum. All the terminal arbors were dynamic, including those with stable dimensions, suggesting that continual remodeling of arbors may be a universal feature of neuronal projections.     

Isolation and characterization of a variant myoblast cell line that is temperature sensitive for differentiation.

A new variant rat myogenic cell line, ts485, was isolated by subcloning the cell line ts3b2 (H. T. Nguyen, R. M. Medford, and B. Nadal-Ginard, Cell 34:281-293, 1983). Unlike the progenitor cell line, ts485 was thermosensitive for differentiation. Experiments with conditioned medium suggested that diffusible extracellular factors were not involved in dictating the differential phenotypes of ts485 cells cultured at the permissive and nonpermissive temperatures. Temperature shift experiments performed on cultures of ts485 cells indicated that the temperature-sensitive lesion was in a factor active during the growth phase and required to trigger a cascade of events leading to terminal differentiation.