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K Janson

Publications and source records attributed to K Janson.

7 recordsLinked to original sources
PubMed2001

Expression of DWnt6, DWnt10, and DFz4 during Drosophila development.

Members of the Wnt gene family encode secreted proteins that signal through the Frizzled family of receptors to function in many aspects of development. In this study, we have analyzed the expression of two Wnt genes and one Frizzled family member that were recently identified through the Drosophila genome sequencing project. We show that DWnt6 is only weakly expressed in developing embryos, with transcripts faintly detected in the gut. By late third instar however, this gene is expressed in a pattern that is identical to that of wingless (wg) in the imaginal discs. DWnt10 is expressed in the embryonic mesoderm, central nervous system and gut, whereas its expression is below the levels of our detection in third instar imaginal discs. We find that DFz4 is also expressed in a dynamic pattern in the mesoderm, gut, and central nervous system.

Animals↗
PubMed2001

Imaging normal and abnormal brain development: new perspectives for child psychiatry.

OBJECTIVE: The availability of non-invasive brain imaging permits the study of normal and abnormal brain development in childhood and adolescence. This paper summarizes current knowledge of brain abnormalities of two conditions, attention deficit hyperactivity disorder (ADHD) and childhood onset schizophrenia (COS), and illustrates how such findings are bringing clinical and preclinical perspectives closer together. METHOD: A selected review is presented of the pattern and temporal characteristics of anatomic brain magnetic resonance imaging (MRI) studies in ADHD and COS. These results are discussed in terms of candidate mechanisms suggested by studies in developmental neuroscience. RESULTS: There are consistent, diagnostically specific patterns of brain abnormality for ADHD and COS. Attention deficit hyperactivity disorder is characterized by a slightly smaller (4%) total brain volume (both white and grey matter), less-consistent abnormalities of the basal ganglia and a striking (15%) decrease in posterior inferior cerebellar vermal volume. These changes do not progress with age. In contrast, patients with COS have smaller brain volume due to a 10% decrease in cortical grey volume. Moreover, in COS there is a progressive loss of regional grey volume particularly in frontal and temporal regions during adolescence. CONCLUSIONS: In ADHD, the developmental pattern suggests an early non-progressive 'lesion' involving neurotrophic factors controlling overall brain growth and selected dopamine circuits. In contrast, in COS, which shows progressive grey matter loss, various candidate processes influencing later synaptic and dendritic pruning are suggested by human post-mortem and developmental animal studies.

Adolescent↗
PubMed1991

A spectrometric study of the Co(2+)-activated ribulose-1,5-bisphosphate carboxylase reaction during turnover and at different pH.

EPR as well as optical absorption studies of the Co(2+)-activated ribulose-1,5-bisphosphate carboxylase/oxygenase under turnover conditions show that the formation of the two detectable intermediates are pH dependent. The amount of one of them, which earlier has been proposed to be a metal coordinated endiol of ribulose-1,5-bisphosphate (Brändén et al. (1987) Biochim. Biophys. Acta 916, 298-303), increased with increasing pH. Distinct optical absorption bands could be assigned to this intermediate and a pH profile could be made. It is therefore proposed that a base with a pKa value of about 8 is responsible for the enzyme-catalysed abstraction of a proton from ribulose-1,5-bisphosphate in order to form the metal coordinated endiol of ribulose-1,5-bisphosphate.

Cobalt↗
PubMed1989

Studies of the Co2+-activated ribulose-1,5-bisphosphate carboxylase/oxygenase by the use of spectrophotometry.

Transient optical absorption bands are formed upon addition of ribulose-1,5-bisphosphate to the Co2+-activated ribulose-1,5-bisphosphate carboxylase/oxygenase from spinach and parsley. In the visible region, the prominent absorption band during steady state has a maximum at 610 nm. Stopped-flow technique was used to study the increase in absorbance at this wavelength, and two distinct phases in the progress curve for the approach to steady-state absorbance were observed. The rates for these two phases, respectively, were similar to those found earlier for the two enzyme-Co2+-bound intermediates using EPR technique (Brändén et al. (1987) Biochim. Biophys. Acta 916, 298-303). It is therefore proposed that most of the transient optical absorption originates from an enzyme-Co2+-coordinated ribulose-1,5-bisphosphate molecule and an enzyme-Co2+-coordinated enediolate anion of it, where bound ribulose-1,5-bisphosphate appears first. Furthermore, the most rapid phase in the progress curve is a first-order reaction, independent of the ribulose-1,5-bisphosphate concentration. This indicates that the formation of enzyme-Co2+-coordinated ribulose-1,5-bisphosphate is preceeded by another reaction in which ribulose-1,5-bisphosphate binds to the enzyme, probably without metal coordination.

Cobalt↗
PubMed1987

Intermediates formed by the Co2+-activated ribulose-1,5-bisphosphate carboxylase/oxygenase from spinach studied by electron paramagnetic resonance spectroscopy.

Two enzyme-metal-bound intermediates formed by the Co2+-activated ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) have been studied by electron paramagnetic resonance (EPR) spectroscopy. Their rates of approach to a stationary state are different and their relative amounts at steady state are dependent on the concentration of ribulose 1,5-bisphosphate. It is therefore proposed that enzyme-metal-coordinated ribulose 1,5-bisphosphate and an enzyme-metal-coordinated enediolate anion of it, where bound ribulose 1,5-bisphosphate appears first, constitute the two EPR-detectable intermediates, respectively.

Cobalt↗