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Robert Mach

Publications and source records attributed to Robert Mach.

4 recordsLinked to original sources
PubMed2025

Comparative genomics and transcriptomics of the Spiroplasma glossinidia strain sGff reveal insights into host interaction and trypanosome resistance in Glossina fuscipes fuscipes.

Tsetse (Glossina spp.) are vectors of African trypanosomes, the causative agents of Human and African Animal trypanosomiases, diseases that remain significant medical and socioeconomic challenges in sub-Saharan Africa. In addition to trypanosomes, tsetse harbor both obligate and facultative symbiotic bacteria that can influence vector competence and reproductive biology. One such facultative symbiont, Spiroplasma glossinidia, infects several tsetse species within the Palpalis subgroup. In Glossina fuscipes fuscipes (Gff), the Spiroplasma glossinidia strain sGff induces a trypanosome-refractory phenotype and negatively impacts reproductive fitness by reducing female fecundity. However, the mechanisms behind these Spiroplasma-derived phenotypes remain poorly understood. Here, we report successful in vitro cultivation of sGff and present complete genomes from three sources: in vitro cultured sGff and sGff isolated from both laboratory-maintained and wild-caught (Uganda) Gff flies. Comparative genomic analyses revealed a high degree of similarity in gene content and synteny among these sGff samples, confirming that they represent isolates of the same strain. Phylogenomic analyses placed sGff within the Spiroplasma poulsonii clade. The sGff genome is highly dynamic, containing numerous mobile genetic elements. Additionally, in silico annotations indicate that sGff relies on its host for both lipids and carbohydrates and produces several toxins, all of which could be implicated in the observed trypanosome refractory phenotype. Finally, comparative transcriptomic analysis of sGff from host hemolymph versus in vitro culture provided insights into potential factors relevant to host-symbiont interactions. Our findings provide a foundation for understanding the nutritional dialogue between sGff and its host and identify symbiotic products that may contribute to trypanosome resistance. Furthermore, the establishment of an in vitro culture system for sGff represents a significant resource for future functional studies with potential implications for vector control.

Glossina fuscipes fuscipes↗
PubMed2006

Modeling vortex swarming in Daphnia.

Based on experimental observations in Daphnia, we introduce an agent-based model for the motion of single and swarms of animals. Each agent is described by a stochastic equation that also considers the conditions for active biological motion. An environmental potential further reflects local conditions for Daphnia, such as attraction to light sources. This model is sufficient to describe the observed cycling behavior of single Daphnia. To simulate vortex swarming of many Daphnia, i.e. the collective rotation of the swarm in one direction, we extend the model by considering avoidance of collisions. Two different ansatzes to model such a behavior are developed and compared. By means of computer simulations of a multi-agent system we show that local avoidance - as a special form of asymmetric repulsion between animals - leads to the emergence of a vortex swarm. The transition from uncorrelated rotation of single agents to the vortex swarming as a function of the swarm size is investigated. Eventually, some evidence of avoidance behavior in Daphnia is provided by comparing experimental and simulation results for two animals.

Animals↗
PubMed2006

Characterization of a novel iodinated sigma-2 receptor ligand as a cell proliferation marker.

Overexpression of sigma-2 receptors in human tumors, such as melanoma, breast cancer, small cell lung carcinoma and prostate cancer, has been reported. Furthermore, the expression of sigma-2 receptors parallels the proliferative status of breast tumors implanted in nude mice. Thus, radiolabeled probes with a high affinity and high selectivity targeting sigma-2 receptors may be useful as tumor imaging agents. A conformationally flexible benzamide derivative, 5-bromo-2,3-dimethoxy-N-[2-(6,7-dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)-butyl]-benzamide, displayed greater than 1,000-fold selectivity for sigma-2 receptors (K(i)=8.2 and 12,900 nM for sigma-2 and sigma-1, respectively). The corresponding radioiodinated ligand, 5-iodo-2,3-dimethoxy-N-[2-(6,7-dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)-butyl]-benzamide ([(125)I]/[(123)I]I), was successfully prepared via an iododestannylation reaction. Binding studies carried out in membrane homogenates prepared from the mouse mammary tumor cell line (EMT6) with [(125)I]I showed the desired high binding affinity and high capacity (K(d)=0.68+/-0.06 nM, B(max)=1,005+/-46 fmol/mg protein). The sigma-2-like pharmacological profile of [(125)I]I binding sites was confirmed by competition studies. Similar binding parameters were also found in EMT6 xenografts (Day 10 and Day 19 implants) from BALB/c mice (K(d)=0.43-1.1 nM, B(max)=2,025-4,528 fmol/mg protein). It was determined by dissection and microSPECT imaging that [(125)I]/[(123)]I accumulated in EMT6 tumors established in BALB/c mice (Day 10 implants). Two hours after the tracer injection, the dissection ratio of EMT6 tumor to background (muscle) reached 6-7. However, microSPECT imaging could not clearly delineate the tumors, while the specific localization could be confirmed by ex vivo autoradiography. In summary, the novel iodinated ligand with high affinity and considerable selectivity for sigma-2 receptors may provide a useful tool to characterize sigma-2 receptors in vitro. Further modification of the ligand and the imaging parameters will be needed to improve the signal for in vivo detection.

Animals↗