Isolation and primary structure of rat secretin

A major form of rat secretin was purified to homogeneity from small intestine, being detected with a porcine secretin radioimmunoassay throughout 7 chromatographic steps. The sequence of the heptacosapeptide amide H-S-D-G-T-F-T-S-E-L-S-R-L-Q-D-S-A-R-L-Q-R-L-L-Q-G-L-V-NH2 shows that rat secretin has a glutamine residue in position 14 instead of arginine as in pig secretin.     

Endo-exonuclease of Aspergillus nidulans

Endo-exonuclease (EE) has been found in both active and inactive, but trypsin-activatable, forms in Aspergillus nidulans. Active EE was present mainly in nuclei, mitochondria, and vacuoles, while trypsin-activatable EE was mainly in the cytosol. The active form accounts for over 90% of the neutral deoxyribonuclease activity extracted from mycelia. A single strand (ss) DNA-binding EE associated with a 28 kilodalton (kDa) polypeptide was partially purified and characterized. It was found to closely resemble, in size and enzymological properties, the ss-DNA-binding EE previously purified from Neurospora crassa. Aspergillus nidulans EE was also found to be immunochemically related to the N. crassa EE and, like that enzyme, was probably derived from a polypeptide of 90 kDa or larger through proteolysis during extraction and purification. It had divalent metal ion-dependent (Mg2+, Mn2+, or Zn2+) activity on both DNA and RNA, which ultimately produced small 5'-P-terminated oligonucleotides. The nuclease activity was mixed endo- and exo-nucleolytic with ss-DNA as substrate, but largely exonucleolytic with double strand (ds) DNA. Superhelical phi X-174 DNA was nicked by EE to form relaxed circular and then linear ds-DNA, which was rapidly degraded to shorter fragments. Linearized pBR322 DNA was extensively nicked internally under conditions where there was relatively low exonuclease activity, but this nicking required that 5'-P-termini be present on the linear ds-DNA. The levels of active EE found in extracts of two recombination-deficient mutants of A. nidulans, uvsC and uvsE, dit not differ significantly from those in extracts of the wild type.     

Differential methylation of the hypervariable locus DXS255 on active and inactive X chromosomes correlates with the expression of a human X-linked gene

Consistent differences in methylation of particular cytosine residues in the DNA of active and inactive X chromosomes can be used for rapid, direct analysis of X-inactivation patterns in different female tissues. We have studied methylation of the highly polymorphic DXS255 locus in tissues from patients with deficiency of the E1 alpha subunit of the pyruvate dehydrogenase complex in whom the results can be correlated directly with total enzyme activity, levels of immunoreactive protein, and patterns of cell mosaicism. The results confirm that methylation of the DXS255 locus correlates with X-chromosome expression. In patients and normal controls, the pattern of X inactivation varied widely from tissue to tissue and often deviated markedly from a 50:50 proportion. These deviations are likely to reflect small numbers of tissue-specific stem cells at the time of random X inactivation and cannot be taken alone as evidence for selection or "nonrandom" inactivation.     

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.     

Soluble and particulate inositol 1,4,5-trisphosphate 5-phosphatases show common antigenic determinants

Inositol 1,4,5-trisphosphate 5-phosphatase catalyses the dephosphorylation of the phosphate in the 5-position from inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate. One particulate and two soluble enzymes were previously described in bovine brain. In this study, we have obtained a precipitating antiserum against soluble type I inositol 1,4,5-trisphosphate 5-phosphatase. The particulate, but not the soluble type II enzyme, was immunoprecipitated by the serum. Inositol 1,4,5-triphosphate 5-phosphatase activity from crude extracts of rat brain, human platelets and rat liver were immmunoprecipitated by the same antibodies, suggesting the existence of common antigenic determinant among inositol 1,4,5-trisphosphate 5-phosphatases of diverse sources.     

Uptake and degradation of hyaluronan in lymphatic tissue.

Afferent lymph vessels entering popliteal lymph nodes of sheep were infused with [3H]acetyl-labelled hyaluronan of high Mr (4.3 x 10(6)-5.5 x 10(6)) and low Mr (1.5 x 10(5)). Analysis of efferent lymph and of residues in the nodes showed that hyaluronan presented by this route is taken up and degraded by lymphatic tissue. Labelled residues isolated in node extracts by gel chromatography and h.p.l.c. included N-acetylglucosamine, acetate, water and a fraction provisionally identified as N-acetylglucosamine 6-phosphate. Between 48 and 75% of the infused material was unrecovered, and had been presumably eliminated through the bloodstream as diffusible residues. Rates of degradation reached as high as 43 micrograms/h in a node of 2 g wt. infused with 56 micrograms/h. Some HA passed into efferent lymph and some was detected in the nodes, but fractions of Mr greater than 1 x 10(6) were not found in either. It is concluded that the amounts and Mr values of hyaluronan released from the tissues into peripheral lymph can be significantly underestimated by analysis of efferent lymph, i.e. lymph that has passed through lymph nodes. A substantial role in the normal metabolic turnover of at least one major constituent of intercellular matrix and connective tissue may now be added to the established functions of the lymphatic system.