On the sufficiency of the velocity field for perception of heading

All models of self-motion from optical flow assume the instantaneous velocity field as input. We tested this assumption for human observers using random-dot displays that simulated translational and circular paths of movement by manipulating the lifetime and displacement of individual dots. For translational movement, observers were equally accurate in judging direction of heading from a velocity field with a two-frame dot life and a direction field in which the magnitudes of displacement were randomized while the radial pattern of directions was preserved, but at chance with a speed field in which the directions were randomized, preserving only magnitude. Accuracy declined with increasing noise in vector directions, but remained below 2.6° with a 90° noise envelope. Thus, the visual system uses the radial morphology of vector directions to determine translational heading and can tolerate large amounts of noise in this pattern. For circular movement, observers were equally accurate with a 2-frame velocity field, 3-frame acceleration displays, and 2-frame and 3-frame direction fields, consistent with the use of the pattern of vector directions to locate the center of rotation. The results indicate that successive independent velocity fields are sufficient for perception of translational and circular heading.     

Lectin binding as a probe of proliferative and differentiative phases in primary monolayer cultures of cutaneous keratinocytes

The surface of cells in the cutaneous epidermis of the newborn rat exhibits a discrete change in lectin-binding specificity from Griffonia simplicifolia I-B4 (GS I-B4), specific for alpha-D-galactosyl residues, to Ulex europeus agglutinin I (UEA), specific for alpha-L-fucose, as the cell leaves the basal layer and differentiates. Primary monolayer cultures of rat keratinocytes maintained in low Ca2+ medium (0.08 mM) exhibited a characteristic unimodal pattern in the ratio of bound UEA to bound GS I-B4 (UEA/B4 ratio) over a 7-day culture period as determined by a quantitative fluorometric assay. The UEA/B4 ratio was initially low between Days 1 and 2 (0.56 +/- 0.05), steadily increased to a maximum of 0.84 +/- 0.09 between Days 2 and 4, and then gradually decreased to 0.41 +/- 0.07 between Days 6 and 7. Estimation of DNA synthesis showed (a) a higher [3H]thymidine incorporation when the UEA/B4 ratio was low and (b) a steady but lower incorporation between Days 3 and 4, coincident with the higher UEA/B4 ratio. Autoradiographic results further showed that cells stained intensely with UEA failed to incorporate [3H]thymidine into their nuclei. Electrophoresis of [3H]fucose-labeled material isolated on UEA-Sepharose 4B revealed that the changes in labeling by [3H]fucose, bound UEA, and the UEA/B4 ratio in the monolayer were related in part to variable expression of "96K-associated UEA-bound" radioactivity corresponding to a major class of lectin-specific cell-surface glycoproteins (GP96 fraction) identified in situ. Overall, the results suggest that (a) the increase in the UEA/B4 ratio between Days 2 and 4 reflects the progression of a proportion of the cells in the monolayer to an early spinous cell stage, the ultimate fate of which is desquamation into the medium and (b) the decrease in the UEA/B4 ratio between Days 5 and 7 reflects a consequent proliferative response to this loss of cells. This system should be useful for studying environmental influences on the homeostasis of cell proliferation and differentiation in the cutaneous epidermis.     

Identification of a cysteine residue as the binding site for the dipyrromethane cofactor at the active site of Escherichia coli porphobilinogen deaminase

The dipyrromethane cofactor of Escherichia coli porphobilinogen deaminase was specifically labelled with 13C by growth of the bacteria in the presence of 5-amino[5-13C]levulinic acid. Using 13C-NMR spectroscopy, the structure of the cofactor was confirmed as a dipyrromethane made up of two linked pyrrole rings each derived from porphobilinogen. The chemical shift data indicate that one of the pyrrole rings of the cofactor is covalently linked to the deaminase enzyme through a cysteine residue. Evidence from protein chemistry studies suggest that cysteine-242 is the covalent binding site for the cofactor.     

Structure and transcription analysis of the gene encoding a cellobiase from Agrobacterium sp. strain ATCC 21400

The DNA sequence was determined for the cloned Agrobacterium sp. strain ATCC 21400 beta-glucosidase gene, abg. High-resolution nuclease S1 protection studies were used to map the abg mRNA 5' and 3' termini. A putative abg promoter was identified whose sequence shows similarities to the consensus promoter of Escherichia coli and with the nif promoter regions of Klebsiella. The abg coding sequence was 1,374 nucleotides long. The molecular weight of the enzyme, based on the predicted amino acid sequence, was 51,000. The observed Mr was 50,000 to 52,000. A region of deduced protein sequence was homologous to a region from two other beta-glucosidase sequences. This region of homology contained a putative active site by analogy with the active site of hen egg white lysozyme.     

The effects of fetal exposure to 1,2-dibromo-3-chloropropane on adult male reproductive function

Several drugs have been shown to cross the placental barrier and affect the fetal testis causing a reduction in testosterone with a resultant impairment of sexual differentiation and an ultimate problem in adult sexual function. In this study, pregnant female rats were treated with 25 mg/kg of the pesticide 1,2-dibromo-3-chloropropane (DBCP). Treatment began on Days 14.5, 16.5, or 18.5 and continued through Day 19.5 of gestation. Some animals were killed on Day 20.5 of intrauterine life and fetal intratesticular testosterone was measured. All other animals were allowed to deliver, and the males were raised to adulthood. At adulthood, body, testis, prostate glands and seminal vesicle weights were recorded. Intratesticular testosterone and luteinizing hormone (LH) receptors were measured. Male and female sexual behavior was quantified and the volume of the sexually dimorphic nucleus of the preoptic area of the hypothalamus was calculated. The histological appearance of the testis was also examined. Treatment for 6 days during fetal life with DBCP decreased intratesticular testosterone by 50% compared to controls at 20.5 days of gestation. At adulthood, all male rats treated during fetal life had a reduced body weight that was correlated with the duration of exposure. Adult testis weight was reduced to 75% of controls as a result of 2 days of fetal exposure to DBCP, whereas 4 and 6 days of exposure during fetal life reduced testis weight by greater than 90%. LH receptors and intratesticular testosterone, in the adults treated during fetal life, were also dramatically reduced.(ABSTRACT TRUNCATED AT 250 WORDS)     

Oligosaccharides from placenta: early diagnosis of feline mannosidosis

High-pressure liquid chromatography analysis of oligosaccharides from placentas allowed the diagnosis of alpha-mannosidosis in three litters of kittens. The chromatography also afforded a detailed comparison of the oligosaccharide pattern and levels in placenta, liver, brain, urine and ocular fluid of the affected animals. In all cases, two series of compounds were observed, with one or two residues of N-acetylglucosamine at the reducing terminus, respectively, and between two and nine mannose residues. This pattern is unlike that of human mannosidosis, and resembles that of ruminants, except that the major oligosaccharide contains three mannose residues instead of two.     

Direct 1H n.m.r. determination of the stereochemical course of hydrolyses catalysed by glucanase components of the cellulase complex

The stereochemical courses of the hydrolyses catalysed by three glycosidases have been determined directly by 1H nmr. The anomeric configuration of the initially formed product was ascertained in each case by observation of the chemical shift and coupling constant of the anomeric proton at the new hemiacetal centre. Two of the enzymes investigated, an endo-glucanase and an exo-glucanase are components of the cellulase complex of Cellulomonas fimi. The third enzyme is the beta-glucosidase from almond emulsin. Two of these enzymes, the exo-glucanase and the almond beta-glucosidase catalysed hydrolysis with retention of anomeric configuration, in agreement with previous observations on the almond enzyme. The endo-glucanase catalysed hydrolysis with inversion of configuration, this result being confirmed by optical rotation measurements. This 1H nmr approach has several advantages over other techniques in that it is applicable to a wide variety of glycosidases and substrates and it is non-destructive, allowing recovery of the enzyme.     

Macrophage growth factor CSF-1 stimulates human monocyte production of interferon, tumor necrosis factor, and colony stimulating activity

CSF-1, a macrophage colony stimulating factor that causes proliferation and differentiation of progenitor cells, may also have effects on mature cells. Human peripheral blood monocytes were used to examine this possibility. Monocytes, separated from normal blood by density centrifugation and adherence, were incubated for 3 days with or without CSF-1 (1,000 U/ml, purified from the MIA PaCa pancreatic carcinoma line). The two groups of cells were then washed and tested for the ability, when induced, to produce several factors. When induced for 2 days with LPS and PMA, the monocytes produced a factor that was cytotoxic to L929 cells, and this factor was completely neutralized by polyclonal antibody to tumor necrosis factor. The cells preincubated with CSF-1 consistently produced an average of 12 times more of this factor than cells not exposed to CSF-1. Monocytes induced with LPS and PMA also produced a colony stimulating activity, as measured by colony formation when using mouse bone marrow. Cells preincubated with CSF-1, washed, and induced with LPS and PMA produced more than three times as much activity compared with control monocytes. When monocytes were induced with poly-I.C, 22-fold higher levels of interferon were produced by the cells exposed to CSF-1. These results show that CSF-1 has direct stimulating effects on mature human monocytes, and suggest that the macrophage growth factor may have clinical application in the treatment of infectious diseases and cancer.     

Studies of comparative infectivity of fifteen strains of Plasmodium vivax to laboratory-reared anopheline mosquitoes, with special reference to Anopheles culicifacies

The Sattoki strain of species A of the taxon Anopheles culicifacies Giles was infected with 15 different strains of Plasmodium vivax from Asia, New Guinea, and Central and South America. A comparison of the relative infectivity indicated a marked variation for the different strains of P. vivax when compared to Anopheles freeborni mosquitoes.