Regulation of an embryogenic carrot gene (DC 2.15) and identification of its active promoter sites

According to previous studies the expression of the geneDC 2.15 is induced in cultured carrot cells after a transfer to an auxin-free medium, where somatic embryo development occurs. This embryogenic gene encodes a prolinerich protein, which resembles proteins involved in auxin-controlled developmental processes. To understand the mechanism underlying the regulation ofDC 2.15, an experimental approach has been employed which allows the direct identification of theDC 2.15 promoter structure by applying PCR techniques. We demonstrate the presence of five distinct promoter sequences highly similar in structure, but slightly different in a common region of about 15 nucleotides, which contain the binding site for the GATA factor originally found in the human HOX gene. Activity of each promoter structure was assessed in developing somatic embryos containing the specific sequence fused to the -glucuronidase (GUS) reporter gene. For two of the five promoter structures a drastic increase in activity was registered during the torpedo stage while the remaining three were inactive throughout the stages of somatic embryogenesis.     

A modular artificial neural net for controlling a six-legged walking system

 A system that controls the leg movement of an animal or a robot walking over irregular ground has to ensure stable support for the body and at the same time propel it forward. To do so, it has to react adaptively to unpredictable features of the environment. As part of our study of the underlying mechanisms, we present here a model for the control of the leg movement of a 6-legged walking system. The model is based on biological data obtained from the stick insect. It represents a combined treatment of realistic kinematics and biologically motivated, adaptive gait generation. The model extends a previous algorithmic model by substituting simple networks of artificial neurons for the algorithms previously used to control leg state and interleg coordination. Each system controlling an individual leg consists of three subnets. A hierarchically superior net contains two sensory and two ‘premotor’ units; it rhythmically suppresses the output of one or the other of the two subordinate nets. These are continuously active. They might be called the ‘swing module’ and the ‘stance module’ because they are responsible for controlling the swing (return stroke) and the stance (power stroke) movements, respectively. The swing module consists of three motor units and seven sensory units. It can produce appropriate return stroke movements for a broad range of initial and final positions, can cope with mechanical disturbances of the leg movement, and is able to react to an obstacle which hinders the normal performance of the swing movement. The complete model is able to walk at different speeds over irregular surfaces. The control system rapidly reestablishes a stable gait when the movement of the legs is disturbed. Received: 13 July 1994/Accepted in revised form: 15 November 1994     

The arsonomethyl group as an analogue of phosphate. An X-ray investigation.

The X-ray structure analysis of three compounds of interest as enzyme substrates is reported. They are the hydrated forms of (I) DL-2-amino-4-arsonobutanoic acid [HO-AsO2--CH2-CH2-CH(NH3+)-CO2H], (II) DL-2-amino-4-phosphonobutanoic acid [HO-PO2--CH2-CH2-CH(NH3+)-CO2H] and the hydrated barium salt of (III) D-3-phosphoglycerate [HO-PO2--O-CH2-CH(OH)-CO2-]. The structures were fully refined to R factors of 0.033, 0.053 and 0.046. For the compounds (I) and (II) the charge distribution was directly determined by locating all H atoms. The co-ordination around As and P is approximately tetrahedral, with the valency angle between the two charged O atoms enlarged to 112 degrees in compound (I), 166 degrees in compound (II) and 122 degrees in compound (III). The As-X bond distances are increased relative to P-X to accommodate the increased atomic radius. The analysis establishes that the compounds are structural analogues. Tables of co-ordinates for H atoms, anisotropic thermal parameters, bond lengths and bond angles for the three compounds have been deposited as Supplementary Publication SUP 50122 (5 pages) with the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained directly [see Biochem J. (1983) 209, 5].     

Systemanalytische Untersuchung eines aufgeschnittenen Regelkreises,der die Beinstellung der Stabheuschrecke Carausius morosus kontrolliert: Kraftmessungen an den Antagonisten Flexor und Extensor tibiae

In the leg of the stick insect Carausius morosus there exists a feedback loop which controls the position of the femur-tibia joint (Bässler, 1965). This feedback mechanism is broken to investigate the open loop system. As output the forces of the two antagonistic muscles flexor tibiae and extensor tibiae are measured separately. As input the feedback transducer of the control mechanism, a chordotonal organ, is stimulated by different kinds of input functions: sine-, step-, delta-, rectangular-and ramp functions. As a qualitative result one can say, that both the flexor-system and the extensor-system have rectifying and high-pass filter properties. However, the comparison between responses to different input functions show that the quantitative properties of this high-pass filter change very strongly with the shape of the input function. Therefore the existence of different nonlinearities has to be assumed.

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Mit Unterstützung der Deutschen Forschungsgemeinschaft (Nr. Ba 578/1)

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Die Arbeit enthält einen Teil der Dissertation von J. Storrer     

The CD20 homologue MS4A4 directs trafficking of KIT toward clathrin-independent endocytosis pathways and thus regulates receptor signaling and recycling

MS4A family members differentially regulate the cell cycle, and aberrant, or loss of, expression of MS4A family proteins has been observed in colon and lung cancer. However, the precise functions of MS4A family proteins and their mechanistic interactions remain unsolved. Here we report that MS4A4 facilitates trafficking of the receptor tyrosine kinase KIT through endocytic recycling rather than degradation pathways by a mechanism that involves recruitment of KIT to caveolin-1–enriched microdomains. Silencing of MS4A4 in human mast cells altered ligand-induced KIT endocytosis pathways and reduced receptor recycling to the cell surface, thus promoting KIT signaling in the endosomes while reducing that in the plasma membrane, as exemplified by Akt and PLCγ1 phosphorylation, respectively. The altered endocytic trafficking of KIT also resulted in an increase in SCF-induced mast cell proliferation and migration, which may reflect altered signaling in these cells. Our data reveal a novel function for MS4A family proteins in regulating trafficking and signaling, which could have implications in both proliferative and immunological diseases.     

Tight turns in stick insects

We investigated insects Carausius morosus walking whilst hanging upside down along a narrow 3 mm horizontal beam. At the end of the beam, the animal takes a 180° turn. This is a difficult situation because substrate area is small and moves relative to the body during the turn. We investigated how leg movements are organised during this turn. A non-contact of either front leg appears to indicate the end of the beam. However, a turn can only begin if the hind legs stand in an appropriate position relative to each other; the outer hind leg must not be placed posterior to the inner hind leg. When starting the turn, both front legs are lifted and usually held in a relatively stable position and then the inner middle leg performs a swing-and-search movement: The leg begins a swing, which is continued by a searching movement to the side and to the rear, and eventually grasps the beam. At the same time the body is turned usually being supported by the outer middle leg and both hind legs. Then front legs followed by the outer middle leg reach the beam. A scheme describing the turns based on a few simple behavioural elements is proposed.     

Controlling a system with redundant degrees of freedom. I. Torque distribution in still standing stick insects

The question is investigated as to how a stick insect solves the task of distributing its body weight onto its six legs, i.e., how are the torques coordinated that are produced by the 18 joints (3 per leg). Three-dimensional force measurements of ground reaction forces have been used to calculate the torques developed by each of the 18 joints. Torques were found to change considerably although the body and the legs of the animal did not move. This result implies a tight cooperation between the 18 joint controllers. Indeed, in each individual experiment, strong correlations could be observed between specific pairs of joints. However, in spite of thorough analysis, no general correlation rules between torques could be detected. The only common attribute found for all experiments was that high absolute torques observed at the beginning of the experiment tend to converge to some minimum over time. Thus, the insects tend to decrease the torques while standing still, but do not use fixed rules. Rather they appear to exploit their extra degrees of freedom and produce time courses that can strongly vary between experiments. Possible mechanisms underlying this behaviour are discussed in a companion paper [Lévy and Cruse (2008) Controlling a system with redundant degrees of freedom: ii. solution of the force distribution problem without a body model, submitted].     

NO donors mimic and NO inhibitors inhibit cytokinin action in betalaineaccumulation in Amaranthus caudatus

A classical biotest for cytokinin is based on the accumulation of betalainesin Amaranthus species. We have shown that inhibitorsof nitric oxide synthase from animals inhibit this response and that chemicaldonors of nitric oxide (NO) stimulate betalaine biosynthesis in Amaranthuscaudatus. NO could be an intermediate in cytokinin signalling.