Histone synthesis and deposition in the G1 and S phases of hepatoma tissue culture cells

Hepatoma tissue culture cells were synchronized in G1 and in S phase in order to examine the level of synthesis of different histone types and to determine the rate, timing, and location of their deposition onto DNA. We observe a basal level of synthesis in G1 (5% of that seen in S phase) for H2A.1, H2A.2, H3.2, H2B, and H4. The minor histone variants X and Z are synthesized at 30% of the rate observed in S cells. The rate of synthesis of the ubiquinated histones uH2A.1,2 is not as depressed in G1 cells as seen for H2A.1 and H2A.2. Histones synthesized in G1 are not deposited on the DNA of these cells at equivalent rates. Thus, histones H3.2 and H4 are not deposited significantly until S phase begins, at which time deposition occurs selectively on newly synthesized DNA. The deposition of H2A.1, H2A.2, H2B, X, and Z proceeds in G1; however, it occurs to a 2-4-fold lower extent than seen for the deposition of H1, HMG 14, and HMG 17. The deposition of all histones synthesized in S phase occurs rapidly, but there are variations in the sites of deposition. Thus, newly synthesized H3.1, H3.2, and H4 deposit primarily on newly replicated DNA whereas H2A.1, H2A.2, uH2A.1, 2, and H2B deposit only partially on new DNA (30%) and mostly on old. H1, HMG 14, and HMG 17 are deposited in an apparently fully random manner over the chromatin. To interpret these observations, we propose a model which includes a measure of histone exchange on the chromatin fiber. The model emphasizes the dynamics of histone-histone and histone-DNA interactions in regions of active genes and at replication forks.     

The spectral sensitivity of eye movements in response to light flashes inDaphnia magna

Summary The crustaceanDaphnia magna responds to a flash of light with a ventral rotation of its compound eye; this behavior is termed eye flick. We determined the spectral sensitivity for the threshold of eye flick in response to light flashes having three different spatial characteristics: (1) full-field, extending 180° from dorsal to ventral in the animal's field of view; (2) dorsal, 30° wide and located in the dorsal region of the visual field; (3) ventral, same as dorsal but located ventrally. All three stimuli extended 30° to the right and to the left of the animal's midplane. We found that spectral sensitivity varies with the spatial characteristics of the stimulus. For full-field illumination, the relative sensitivity was maximal at 527 nm and between 365 nm and 400 nm, with a significant local minimum at 420 nm. For the dorsal stimulus, the relative sensitivity was greatest at 400 nm, but also showed local maxima at 440 nm and 517 nm. For the ventral stimulus, the relative sensitivity maxima occurred at the same wavelengths as those for the full-field stimulus. At wavelengths of 570 nm and longer, the responses to both dorsal and ventral stimuli showed lower relative sensitivity than the full-field stimulus. No circadian or other periodic changes in threshold spectral sensitivity were observed under our experimental conditions. Animals which had their nauplius eyes removed by means of laser microsurgery had the same spectral sensitivity to full-field illumination as normal animals. Our results are discussed in terms of our current knowledge of the spectral classes of photoreceptors found in theDaphnia compound eye.     

The spread of somatosensory-evoked potentials within the nervous system

Four thalamic and cortical recordings were carried out in 5 patients. The thalamic-evoked potentials were typical and revealed a triphasic complex, but their latencies showed a relatively high standard deviation. They could be divided into two groups according to their latencies, both of which had low SD. These data suggested that there could be two types of latency of thalamic SEP, because the 4 patients' body sizes were very similar. More detailed surface, cortical and depth recordings are needed to resolve these questions.     

Growth inhibitory effects of 5-aza-2'-deoxycytidine in HL-60 promyelocytic leukemia cells resistant to differentiation induction

In the original HL-60 cells (HL-60-S) and an HL-60 subline (HL-60-R) respectively susceptible and resistant to induction of differentiation by retinoic acid or dimethyl sulfoxide, 5-aza-2'-deoxycytidine inhibited growth equally but induced differentiation to a greater extent in HL-60-S. Flow cytometry showed that 5-aza-2'-deoxycytidine produced in both HL-60 lines an increased proportion of cells in G2+M rather than G0/G1 as with retinoic acid. 5-aza-2'-deoxycytidine may have a differentiation-inducing effect in HL-60 provided cells have the competence to differentiate, indicating the importance of an alternate mechanism of action.     

Diagnostic test systems based on the immunoenzyme method in leprosy

Diagnostic test systems for the detection of IgG and IgM to Mycobacterium leprae in the blood sera of leprosy patients and armadillos experimentally infected with M. leprae have been developed on the basis of the indirect immunoperoxidase assay. The possibility has been shown of prognosing the activity of the leprotic process in leprosy patients and the results of the experimental infection of armadillos by the dynamic increase of antibody reactions with the development of the infection.     

Digestion in the cattle-tick Boophilus microplus: light microscope study of the gut cells in nymphs and females

The gut caeca of B. microplus were studied by light microscopy using paraffin and methacrylate embedded material. It has been shown that during feeding of nymphs and adults, the midgut consists of five cell types, stem cell, digest cell, secretory cells (s₁) and (s₂) and basophilic cell. The stem cell differentiates into any of the other cell types. The digest cell matures through a series of stages and has up to three generations during feeding on the host. The final generation has two distinct cell types, the first type is thought to be capable of both phagocytosis and pinocytosis. Cells of the second type are predominant at the end of feeding, and may be specialized to ingest and digest haemoglobin. The final stage of the digest series is the spent digest cell which discharges its content into the gut lumen or is excreted whole. The basophilic cell has structures which suggest that one of its functions is to transport digested materials, water and ions across the gut. Secretory cell (s₁) secretes a glycoprotein which may be a haemolysin and secretory cell (s₂) secretes the gut “colloid” mass, an acid mucopolysaccharide, which may function as an anticoagulant. Intracellular digestion leads to the breakdown of host blood and storage of lipid and glycogen in the digest cells.