University of Hamburg

About: University of Hamburg is a education organization based out in Hamburg, Germany. It is known for research contribution in the topics: Population & Laser. The organization has 45564 authors who have published 89286 publications receiving 2850161 citations. The organization is also known as: Hamburg University.

Molecular principles of hair follicle induction and morphogenesis.

Abstract: Hair follicle (HF) development is the result of neuroectodermal-mesodermal interactions, and can be divided into morphologically distinguishable stages (induction, organogenesis and cytodifferentiation). The spacing, polarity and differentiation patterns of HFs are driven by interacting, self-assembling gradients of inhibitors and activators, which are established jointly by the skin epithelium and mesenchyme. For HF development to occur, the dominant-negative influence of inhibitors of the HF differentiation pathway must be locally counteracted by specific antagonists and/or overriden by stimulators of hair placode formation. Once a mesenchymal condensate of inductive fibroblasts has formed, it takes over control of most subsequent steps of HF organogenesis and of epithelial stem cell differentiation into distinct lineages. In this review we introduce the morphological characteristics, major underlying principles and molecular key players that control HF development. The focus is on recent insights into the molecular interactions leading to hair follicle induction, and we close with synthesizing a corresponding working hypothesis.

Critical temperatures for xylogenesis in conifers of cold climates

Abstract: Aim To identify temperatures at which cell division and differentiation are active in order to verify the existence of a common critical temperature determining growth in conifers of cold climates. Location Ten European and Canadian sites at different latitudes and altitudes. Methods The periods of cambial activity and cell differentiation were assessed on a weekly time-scale on histological sections of cambium and wood tissue collected over 2 to 5 years per site from 1998 to 2005 from the stems of seven conifer species. All data were compared with daily air temperatures recorded from weather stations located close to the sites. Logistic regressions were used to calculate the probability of xylogenesis and of cambium being active at a given temperature. Results Xylogenesis lasted from May to October, with a growing period varying from 3 to 5 months depending on location and elevation. Despite the wide geographical range of the monitored sites, temperatures for onset and ending of xylogenesis converged towards narrow ranges with average values around 4–5, 8–9 and 13–14 °C for daily minimum, mean and maximum temperature, respectively. On the contrary, cell division in the cambium stopped in July−August, when temperatures were still high. Main conclusions Wood formation in conifers occurred when specific critical temperatures were reached. Although the timing and duration of xylogenesis varied among species, sites and years, the estimated temperatures were stable for all trees studied. These results provide biologically based evidence that temperature is a critical factor limiting production and differentiation of xylem cells in cold climates. Although daily temperatures below 4−5 °C are still favourable for photosynthesis, thermal conditions below these values could inhibit the allocation of assimilated carbon to structural investment, i.e. xylem growth.

Parent-of-origin-specific allelic associations among 106 genomic loci for age at menarche

Abstract: Age at menarche is a marker of timing of puberty in females. It varies widely between individuals, is a heritable trait and is associated with risks for obesity, type 2 diabetes, cardiovascular disease, breast cancer and all-cause mortality. Studies of rare human disorders of puberty and animal models point to a complex hypothalamic-pituitary-hormonal regulation, but the mechanisms that determine pubertal timing and underlie its links to disease risk remain unclear. Here, using genome-wide and custom-genotyping arrays in up to 182,416 women of European descent from 57 studies, we found robust evidence (P < 5 × 10(-8)) for 123 signals at 106 genomic loci associated with age at menarche. Many loci were associated with other pubertal traits in both sexes, and there was substantial overlap with genes implicated in body mass index and various diseases, including rare disorders of puberty. Menarche signals were enriched in imprinted regions, with three loci (DLK1-WDR25, MKRN3-MAGEL2 and KCNK9) demonstrating parent-of-origin-specific associations concordant with known parental expression patterns. Pathway analyses implicated nuclear hormone receptors, particularly retinoic acid and γ-aminobutyric acid-B2 receptor signalling, among novel mechanisms that regulate pubertal timing in humans. Our findings suggest a genetic architecture involving at least hundreds of common variants in the coordinated timing of the pubertal transition.