Humboldt University of Berlin

About: Humboldt University of Berlin is a education organization based out in Berlin, Germany. It is known for research contribution in the topics: Population & Medicine. The organization has 33671 authors who have published 61781 publications receiving 1908102 citations. The organization is also known as: Humboldt-Universität zu Berlin & Universitas Humboldtiana Berolinensis.

Fundamental growth principles of colloidal metal nanoparticles – a new perspective

Abstract: In the past few decades, much effort was put into the development of synthetic strategies to produce nanoparticles of different sizes and morphologies and a large number of scientific contributions is dedicated to the characterization and application of metal nanoparticles. In contrast, only few studies deal with particle formation mechanisms. As a consequence, theoretical concepts that describe particle growth processes are very rare and the few existing models are hardly able to explain how synthesis parameters influence the final particle size distribution. This contribution discusses recent experimental results from which a novel growth concept based on colloidal stability is deduced. The growth concept is in contrast to nucleation models and allows a description of colloidal growth processes from a different perspective. It states that for most syntheses the minimal particle size is rather determined by colloidal than thermodynamic stability making a nucleation model irrelevant.

Multi-ancestry genome-wide association study of 21,000 cases and 95,000 controls identifies new risk loci for atopic dermatitis

Abstract: Genetic association studies have identified 21 loci associated with atopic dermatitis risk predominantly in populations of European ancestry. To identify further susceptibility loci for this common, complex skin disease, we performed a meta-analysis of >15 million genetic variants in 21,399 cases and 95,464 controls from populations of European, African, Japanese and Latino ancestry, followed by replication in 32,059 cases and 228,628 controls from 18 studies. We identified ten new risk loci, bringing the total number of known atopic dermatitis risk loci to 31 (with new secondary signals at four of these loci). Notably, the new loci include candidate genes with roles in the regulation of innate host defenses and T cell function, underscoring the important contribution of (auto)immune mechanisms to atopic dermatitis pathogenesis.

A universal model for spike-frequency adaptation

Abstract: Spike-frequency adaptation is a prominent feature of neural dynamics. Among other mechanisms, various ionic currents modulating spike generation cause this type of neural adaptation. Prominent examples are voltage-gated potassium currents (M-type currents), the interplay of calcium currents and intracellular calcium dynamics with calcium-gated potassium channels (AHP-type currents), and the slow recovery from inactivation of the fast sodium current. While recent modeling studies have focused on the effects of specific adaptation currents, we derive a universal model for the firing-frequency dynamics of an adapting neuron that is independent of the specific adaptation process and spike generator. The model is completely defined by the neuron's onset f-I curve, the steady-state f-I curve, and the time constant of adaptation. For a specific neuron, these parameters can be easily determined from electrophysiological measurements without any pharmacological manipulations. At the same time, the simplicity of the model allows one to analyze mathematically how adaptation influences signal processing on the single-neuron level. In particular, we elucidate the specific nature of high-pass filter properties caused by spike-frequency adaptation. The model is limited to firing frequencies higher than the reciprocal adaptation time constant and to moderate fluctuations of the adaptation and the input current. As an extension of the model, we introduce a framework for combining an arbitrary spike generator with a generalized adaptation current.

Tight regulation of unstructured proteins: from transcript synthesis to protein degradation.

Abstract: Altered abundance of several intrinsically unstructured proteins (IUPs) has been associated with perturbed cellular signaling that may lead to pathological conditions such as cancer. Therefore, it is important to understand how cells precisely regulate the availability of IUPs. We observed that regulation of transcript clearance, proteolytic degradation, and translational rate contribute to controlling the abundance of IUPs, some of which are present in low amounts and for short periods of time. Abundant phosphorylation and low stochasticity in transcription and translation indicate that the availability of IUPs can be finely tuned. Fidelity in signaling may require that most IUPs be available in appropriate amounts and not present longer than needed.

Tendon healing in a bone tunnel. Part II: Histologic analysis after biodegradable interference fit fixation in a model of anterior cruciate ligament reconstruction in sheep.

Abstract: Purpose: Tendon-to-bone healing of soft-tissue grafts has been described to progress by the development of a fibrous interzone that undergoes a maturation process leading to the development of an indirect type of ligament insertion. Previous studies used extra-articular models or fixation far away from the joint line; thus, no data are available investigating tendon-to-bone healing of a soft-tissue graft fixed anatomically. Therefore, we studied the tendon-to-bone healing of the anatomic soft-tissue graft interference fit fixation in a model of anterior cruciate ligament (ACL) reconstruction in sheep. Type of Study: Animal study. Methods: Thirty-five mature sheep underwent ACL reconstruction with an autologous Achilles tendon split graft. Grafts were directly fixed with biodegradable poly-(D,L-lactide) interference screws. Animals were euthanized after 6, 9, 12, 24, and 52 weeks and histologic evaluations were performed. Undecalcified specimens were evaluated under normal and polarized light. Additionally, animals received a polychrome sequential labeling (tetracycline, xylenol orange, and calcein green) to determine bone growth per time under fluorescent light. Results: Intratunnel histologic findings at 6 weeks showed a tendon-bone junction with only a partial fibrous interzone between the graft tissue and the surrounding bone. A mature intratunnel tendon-bone junction with a zone of fibrocartilage was found at 9 to 12 weeks. At the tunnel entrance site a wide regular ligamentous insertion site was seen in all specimens after 24 weeks. This insertion showed regular patterns such as the direct type of insertion of a normal ligament with a dense basophilic transition zone consisting of mineralized cartilage. Conclusions: A fibrous interzone between the graft tissue and the bone tunnel was only partially developed, which is in contrast to all previous studies in which nonanatomic fixation was used. Thus, it is reasonable to assume that the tendon-to-bone healing in the present study may progress partially by direct-contact healing without the development of a fibrous interzone. To our knowledge, this is the first report describing the development of a direct type of ligament insertion after ACL replacement with a soft-tissue graft. This is in contrast to previous studies reporting the development of an indirect type of insertion when using nonanatomic fixation far away from the joint line. Thus, histologic data strongly indicate that anatomic interference fit fixation is beneficial for tendon-to-bone incorporation by leading to the development of a direct type of ligament insertion. Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 18, No 2 (February), 2002: pp 124–135