Photoreceptor projection and termination pattern in the lamina of gonodactyloid stomatopods (mantis shrimp)

The apposition compound eyes of gonodactyloid stomatopods are divided into a ventral and a dorsal hemisphere by six equatorial rows of enlarged ommatidia, the mid-band (MB). Whereas the hemispheres are specialized for spatial vision, the MB consists of four dorsal rows of ommatidia specialized for colour vision and two ventral rows specialized for polarization vision. The eight retinula cell axons (RCAs) from each ommatidium project retinotopically onto one corresponding lamina cartridge, so that the three retinal data streams (spatial, colour and polarization) remain anatomically separated. This study investigates whether the retinal specializations are reflected in differences in the RCA arrangement within the corresponding lamina cartridges. We have found that, in all three eye regions, the seven short visual fibres (svfs) formed by retinula cells 1–7 (R1–R7) terminate at two distinct lamina levels, geometrically separating the terminals of photoreceptors sensitive to either orthogonal e-vector directions or different wavelengths of light. This arrangement is required for the establishment of spectral and polarization opponency mechanisms. The long visual fibres (lvfs) of the eighth retinula cells (R8) pass through the lamina and project retinotopically to the distal medulla externa. Differences between the three eye regions exist in the packing of svf terminals and in the branching patterns of the lvfs within the lamina. We hypothesize that the R8 cells of MB rows 1–4 are incorporated into the colour vision system formed by R1–R7, whereas the R8 cells of MB rows 5 and 6 form a separate neural channel from R1 to R7 for polarization processing.This research was supported by the Swiss National Science Foundation (PBSKB-104268/1), the Australian Research Council (LP0214956) and the American Air Force (AOARD/AFOSR) (F62562-03-P-0227).     

Characterizing associations and SNP-environment interactions for GWAS-identified prostate cancer risk markers--results from BPC3

Genome-wide association studies (GWAS) have identified multiple single nucleotide polymorphisms (SNPs) associated with prostate cancer risk. However, whether these associations can be consistently replicated, vary with disease aggressiveness (tumor stage and grade) and/or interact with non-genetic potential risk factors or other SNPs is unknown. We therefore genotyped 39 SNPs from regions identified by several prostate cancer GWAS in 10,501 prostate cancer cases and 10,831 controls from the NCI Breast and Prostate Cancer Cohort Consortium (BPC3). We replicated 36 out of 39 SNPs (P-values ranging from 0.01 to 10⁻²⁸). Two SNPs located near KLK3 associated with PSA levels showed differential association with Gleason grade (rs2735839, P = 0.0001 and rs266849, P = 0.0004; case-only test), where the alleles associated with decreasing PSA levels were inversely associated with low-grade (as defined by Gleason grade <8) tumors but positively associated with high-grade tumors. No other SNP showed differential associations according to disease stage or grade. We observed no effect modification by SNP for association with age at diagnosis, family history of prostate cancer, diabetes, BMI, height, smoking or alcohol intake. Moreover, we found no evidence of pair-wise SNP-SNP interactions. While these SNPs represent new independent risk factors for prostate cancer, we saw little evidence for effect modification by other SNPs or by the environmental factors examined.     

Modifications to a molt‐based ageing system proposed by Wolfe et al. (2010)

ABSTRACT Wolfe et al. (2010 . Journal of Field Ornithology 81: 186–194) proposed a coding system for ageing birds based on the sequence of molts and plumages, which is more practical than a calendar‐based system, especially in tropical and southern latitudes where species often breed across 1 January. The Wolfe–Ryder–Pyle (hereafter, W–R–P) three‐letter system is based on recognition of molt cycle (first, second, third, definitive, and so on) and plumage phase (juvenile, supplemental, formative, alternate, and basic). For example, a bird in First Cycle Formative plumage is coded as FCF. We propose the use of two additional code options that further refine age brackets. First, we suggest the use of an “after” or “A” code in place of the “C,” or cycle code, where an earlier molt cycle or plumage can be ruled out. For example, a bird that exhibits Staffelmauser might be aged as after‐third cycle basic, or TAB. Second, we suggest using “pre” or “P” in place of the “C,” or cycle code, when birds are actively molting, such as for birds undergoing the second prebasic molt or SPB. For both codes, we discuss their applicability using examples based on actual banding data. Our proposed codes will improve the utility of the W–R–P system by better refining age brackets and by expanding its applicability to a diverse array of taxa.     

Antheseabhängige UV-Muster in Blütenständen von Asteraceen

The pseudanthia ofHeliopsis scabra andRudbeckia vulgaris (Asteraceae) were examined during the anthesis for differences in their UV patterns. Distinct changes in the reflectance and absorbance properties could be observed. The results suggest a close correlation between different stages of floral development and pollinator attraction.

Herrn Prof. Dr.Lothar Geitler zum 90. Geburtstag gewidmet.     

Functional Promiscuity of Gene Regulation by Serpentine Receptors in Dictyostelium discoideum

Serpentine receptors such as smoothened and frizzled play important roles in cell fate determination during animal development. In Dictyostelium discoideum, four serpentine cyclic AMP (cAMP) receptors (cARs) regulate expression of multiple classes of developmental genes. To understand their function, it is essential to know whether each cAR is coupled to a specific gene regulatory pathway or whether specificity results from the different developmental regulation of individual cARs. To distinguish between these possibilities, we measured gene induction in car1 car3 double mutant cell lines that express equal levels of either cAR1, cAR2, or cAR3 under a constitutive promoter. We found that all cARs efficiently mediate both aggregative gene induction by cAMP pulses and induction of postaggregative and prespore genes by persistent cAMP stimulation. Two exceptions to this functional promiscuity were observed. (i) Only cAR1 can mediate adenosine inhibition of cAMP-induced prespore gene expression, a phenomenon that was found earlier in wild-type cells. cAR1’s mediation of adenosine inhibition suggests that cAR1 normally mediates prespore gene induction. (ii) Only cAR2 allows entry into the prestalk pathway. Prestalk gene expression is induced by differentiation-inducing factor (DIF) but only after cells have been prestimulated with cAMP. We found that DIF-induced prestalk gene expression is 10 times higher in constitutive cAR2 expressors than in constitutive cAR1 or cAR3 expressors (which still have endogenous cAR2), suggesting that cAR2 mediates induction of DIF competence. Since in wild-type slugs cAR2 is expressed only in anterior cells, this could explain the so far puzzling observations that prestalk cells differentiate at the anterior region but that DIF levels are actually higher at the posterior region. After the initial induction of DIF competence, cAMP becomes a repressor of prestalk gene expression. This function can again be mediated by cAR1, cAR2, and cAR3.Recent years have seen the discovery of critical roles in animal development for serpentine receptors, which are usually coupled to heterotrimeric G proteins. The insect sigaling peptides hedgehog and wingless and their mammalian counterparts sonic hedgehog, desert hedgehog, and indian hedgehog and the wnt factors control a multitude of inductive events during all stages of embryogenesis. The hedgehog signal is detected by two different serpentine receptors, smoothened (1, 40) and patched (21, 38), whereas the wingless or wnt signal is detected by the serpentine receptor D-frizzled-2 (3). In the social amoeba Dictyostelium discoideum, serpentine cyclic AMP (cAMP) receptors (cARs) control induction of cell differentiation during the entire course of development. Starving cells secrete cAMP pulses that induce chemotaxis and expression of genes required for the aggregation process. Cells aggregate to form mounds, which ultimately transform into fruiting structures that consist of a globular spore mass supported by a column of stalk cells. cAMP induces entry into the spore differentiation pathway as well as synthesis of a lipophilic factor, differentiation-inducing factor (DIF), which induces entry into the stalk differentiation pathway (see reference 5). At an early stage of development cAMP synergizes with DIF to induce prestalk genes, but later it becomes an inhibitor of stalk gene expression (2). cARs were shown previously to mediate induction of aggregative genes by cAMP pulses (20) as well as cAMP induction of prespore genes and repression of prestalk genes (31, 37). Remarkably, the target for the latter critical step in cell fate determination is glycogen synthase kinase 3 (GSK-3), a zeste white-3 homolog, which is the target for the effects of wingless and wnt in insects and vertebrates, respectively (7, 34).Four cARs, showing 54 to 69% amino acid identity, are expressed in a stage- and cell-type-specific manner. cAR1 is predominantly expressed before and during aggregation (18). cAR3 is expressed at late aggregation, and expression is later restricted to the prespore cell population (13, 44). cAR2 and cAR4 are both expressed exclusively in the prestalk cell population after aggregation (19, 30). cAR knockout cell lines were generated to examine the role of the individual cARs in Dictyostelium development. car1 null cells neither aggregate nor express developmental genes but can be triggered to express aggregative and postaggregative genes by stimulation with cAMP (37, 39). car3 null cells aggregate and develop normally (13). car1 car3 double gene disruptants do not aggregate, and developmental gene expression cannot be restored with cAMP, indicating that cAR1 or cAR3 shows functional redundancy and that either one or the other has to be present for gene induction to occur (10, 36). car2 null cells are blocked in the mound stage, while car4 null cells show abnormal slug morphogenesis and culmination. Both lines show reduced expression of prestalk genes and enhanced expression of prespore genes (19, 29).To understand the function of the four cARs, it is essential to know whether each receptor is coupled to a specific signal transduction pathway that controls a specific cell differentiation event or whether each receptor can activate multiple cell differentiation pathways. In the latter case, it is not the presence of a specific receptor that determines whether a response occurs but the availability of the downstream signaling pathway. To determine whether individual receptors have unique functions in developmental gene expression, we examined gene regulation in cell lines that display about equal levels of cAR1, cAR2, and cAR3 in a car1 car3 mutant background. Our results show that with two exceptions, all three receptors can transduce both the excitation and adaptation components of the different cAMP-regulated gene induction events with almost equal levels of efficiency.     

GTPase activity of the stimulatory GTP-binding regulatory protein of adenylate cyclase, Gs. Accumulation and turnover of enzyme-nucleotide intermediates

The GTPase activity of the stimulatory guanine nucleotide-binding regulatory protein (Gs) of hormone-sensitive adenylate cyclase was investigated using purified rabbit hepatic Gs and either [alpha-32P]- or [gamma-32P] GTP as substrate. The binding of [35S]guanosine 5'-O-(thiotriphosphate) (GTP gamma S) was used to quantitate the total concentration of Gs. 1) GTPase activity was a saturable function of the concentration of GTP, with Km = 0.3 microM. MgCl2 monotonically increased the activity. The maximum observed turnover number was about 1.5 min-1. 2) During steady-state hydrolysis, 20-40% of total Gs could be trapped as a Gs-GDP complex and 1-2% could be trapped as Gs-GTP. The hydrolysis of Gs-GTP to Gs-GDP occurred with t 1/2 less than or equal to 5 s at 30 degrees C and t 1/2 approximately 1 min at 0 degrees C. Hydrolysis of Gs-GTP was inhibited by 1.0 mM EDTA in the absence of added Mg2+. 3) The rate of formation of Gs-GDP and the initial GTPase rate varied in parallel as functions of the concentrations of either GTP or MgCl2 (above 0.1 mM Mg2+). The ratio of the rate of accumulation of Gs-GDP to the GTPase rate was constant at 0.3-0.4. 4) The rate of dissociation of assayable Gs-GDP was biphasic. The initial phase accounted for 60-80% of total assayable Gs-GDP and was characterized by a t 1/2 of about 1 min. 5) Lubrol 12A9 potently inhibited the GTPase reaction and the dissociation of Gs-GDP in parallel, and inhibition of product release may account for the inhibition of steady-state hydrolysis. 6) The beta and gamma subunits of Gs markedly inhibited the dissociation of GDP from Gs in contrast to their ability to stimulate the dissociation of GTP gamma S. 7) GDP, GTP gamma S, and guanyl-5'-yl imidodiphosphate (Gpp(NH)p) competitively inhibited the accumulation of Gs-GDP. GTP gamma S and Gpp(NH)p inhibited the GTPase reaction noncompetitively, GDP displayed mixed inhibition, and Pi did not inhibit. These data are interpretable in terms of the coexistence of two specific mechanistic pathways for the overall GTPase reaction.     

Single amino acids in the lumenal loop domain influence the stability of the major light-harvesting chlorophyll a/b complex

The major light-harvesting complex of photosystem II (LHCIIb) is one of the most abundant integral membrane proteins. It greatly enhances the efficiency of photosynthesis in green plants by binding a large number of accessory pigments that absorb light energy and conduct it toward the photosynthetic reaction centers. Most of these pigments are associated with the three transmembrane and one amphiphilic alpha helices of the protein. Less is known about the significance of the loop domains connecting the alpha helices for pigment binding. Therefore, we randomly exchanged single amino acids in the lumenal loop domain of the bacterially expressed apoprotein Lhcb1 and then reconstituted the mutant protein with pigments in vitro. The resulting collection of mutated recombinant LHCIIb versions was screened by using a 96-well-format plate-based procedure described previously [Heinemann, B., and Paulsen, H. (1999) Biochemistry 38, 14088-14093], enabling us to test several thousand mutants for their ability to form stable pigment-protein complexes in vitro. At least one-third of the positions in the loop domain turned out to be sensitive targets; i.e., their exchange abolished formation of LHCIIb in vitro. This confirms our earlier notion that the LHCIIb loop domains contribute more specifically to complex formation and/or stabilization than by merely connecting the alpha helices. Among the target sites, glycines and hydrophilic amino acids are more prominently represented than hydrophobic ones. Specifically, the exchange of any of the three acidic amino acids in the lumenal loop abolishes reconstitution of stable pigment-protein complexes, suggesting that ionic interactions with other protein domains are important for correct protein folding or complex stabilization. One hydrophobic amino acid, tryptophan in position 97, has been hit repeatedly in independent mutation experiments. From the LHCIIb structure and previous mutational analyses, we propose a stabilizing interaction between this amino acid and F195 near the C-proximal end of the third transmembrane helix.     

Peroxiredoxin I and II in Human Eyes: Cellular Distribution and Association with Pterygium and DNA Damage

Peroxiredoxin I and II are both 2-Cys members of the peroxiredoxin family of antioxidant enzymes and inactivate hydrogen peroxide. On western blotting, both enzymes appeared as 22-kD proteins and were present in the sclera, retina and iris. Immunohistochemistry showed strong cytoplasmic labeling in the basal cells of the corneal epithelial layer and the corneoscleral limbus. The melanocytes within the stroma of the iris and the anterior epithelial cells of the lens also showed strong cytoplasmic labeling. The fibrous structure of the stroma and the posterior surface of the ciliary body were also labeled. There was also strong labeling for both enzymes in the photoreceptors and the inner and outer plexiform layers of the retina. There was increased labeling of peroxiredoxin I and II in pterygium. In normal conjunctiva and cornea, only the basal cell layer showed labeling for peroxiredoxin I and II, whereas, in pterygia, there was strong cytoplasmic labeling in most cells involving the full thickness of the epithelium. Co-localization of the DNA oxidation product 8-hydroxy-2’-deoxyguanosine antibody with the nuclear dye 4’,6’-diamidino-2-phenylindole dihydrochloride indicated that the majority of the oxidative damage was cytoplasmic; this suggested that the mitochondrial DNA was most affected by the UV radiation in this condition.