Characterization of SPACR, a sialoprotein associated with cones and rods present in the interphotoreceptor matrix of the human retina: immunological and lectin binding analysis

Rod and cone photoreceptors project from the outer retinal surface into a carbohydrate-rich interphotoreceptor matrix (IPM). Unique IPM glycoconjugates are distributed around rods and cones. Wheat germ agglutinin (WGA) strongly decorates the rod matrix domains and weakly decorates the cone matrix domains. This study characterizes the major WGA-binding glycoprotein in the human IPM, which we refer to as SPACR (sialoprotein associated with cones and rods). SPACR, which has a molecular weight of 147 kDa, was isolated and purified from the IPM by lectin affinity chromatography. A polyclonal antibody to SPACR was prepared that colocalizes in tissue preparations with WGA-binding domains in the IPM. Sequential digestion of SPACR with N- and O- glycosidases results in a systematic increase in electrophorectic mobility, indicating the presence of both N- and O-linked glycoconjugates. Complete deglycosylation results in a reduction in the relative molecular mass of SPACR by about 30%. Analysis of lectin binding allowed us to identify some of the structural characteristics of SPACR glycoconjugates. Treatment with neuraminidase exposes Galbeta1- 3GalNAc disaccharide as indicated by positive peanut agglutinin (PNA) staining, accompanied by the loss of WGA staining. Maackia amurensis agglutinins (MAA-1 and MAA-2), specific for sialic acid in alpha2-3 linkage to Gal, bind SPACR, while Sambucus nigra agglutinin (SNA), specific for alpha2-6 linked sialic acid, does not, indicating that the dominant glycoconjugate determinant on SPACR is the O-linked carbohydrate, NeuAcalpha2-3Galbeta1-3GalNAc. The abundance of sialic acid in SPACR suggests that this glycoprotein may contribute substantially to the polyanionic nature of the IPM. The carbohydrate chains present on SPACR could also provide sites for extensive crosslinking and participate in the formation of the ordered IPM lattice that surrounds the elongate photoreceptors projecting from the outer retinal surface.      

Predation risk and mating behavior: the responses of moths to bat-like ultrasound

In the presence of predators, animals may reduce or alter theirmating activities. There has been little experimental studyof whether mating behavior varies with the level of predationrisk. Two species of moths, Pseudaletia unipuncta (Noctuidae)and Ostrinia nubilalis (Pyralidae), significantly reduced theirmate-seeking behavior under high levels of simulated predationrisk. Male moths aborted upwind flight in a pheromone plume,and females stopped releasing pheromone in response to soundssimulating the echolocation calls of bats. For O. nubilalis,but not for P. unipuncta, the response varied significantlywith the level of predation risk. Interspecific differencesin behavioral responses likely reflect differences in physiologicalauditory sensitivity and/or behavioral thresholds. Female behavioralresponses to sounds simulating the calls of bats that gleantheir prey from surfaces were significantly weaker than theirresponses to sounds resembling the calls of aerially hawkingbats; these results support the neurophysiological data thatthe calls of gleaning bats are relatively inaudible to moths.This study indicates that some animals can modify their reproductiveactivities in response to auditory cues from predators.     

A Versatile Click-Compatible Monolignol Probe to Study Lignin Deposition in Plant Cell Walls

Lignin plays important structural and functional roles in plants by forming a hydrophobic matrix in secondary cell walls that enhances mechanical strength and resists microbial decay. While the importance of the lignin matrix is well documented and the biosynthetic pathways for monolignols are known, the process by which lignin precursors or monolignols are transported and polymerized to form this matrix remains a subject of considerable debate. In this study, we have synthesized and tested an analog of coniferyl alcohol that has been modified to contain an ethynyl group at the C-3 position. This modification enables fluorescent tagging and imaging of this molecule after its incorporation into plant tissue by click chemistry-assisted covalent labeling with a fluorescent azide dye, and confers a distinct Raman signature that could be used for Raman imaging. We found that this monolignol analog is incorporated into in vitro-polymerized dehydrogenation polymer (DHP) lignin and into root epidermal cell walls of 4-day-old Arabidopsis seedlings. Incorporation of the analog in stem sections of 6-week-old Arabidopsis thaliana plants and labeling with an Alexa-594 azide dye revealed the precise locations of new lignin polymerization. Results from this study indicate that this molecule can provide high-resolution localization of lignification during plant cell wall maturation and lignin matrix assembly.     

Indirect selection of thermal tolerance during experimental evolution of Drosophila melanogaster

Natural selection alters the distribution of a trait in a population and indirectly alters the distribution of genetically correlated traits. Long‐standing models of thermal adaptation assume that trade‐offs exist between fitness at different temperatures; however, experimental evolution often fails to reveal such trade‐offs. Here, we show that adaptation to benign temperatures in experimental populations of Drosophila melanogaster resulted in correlated responses at the boundaries of the thermal niche. Specifically, adaptation to fluctuating temperatures (16–25°C) decreased tolerance of extreme heat. Surprisingly, flies adapted to a constant temperature of 25°C had greater cold tolerance than did flies adapted to other thermal conditions, including a constant temperature of 16°C. As our populations were never exposed to extreme temperatures during selection, divergence of thermal tolerance likely reflects indirect selection of standing genetic variation via linkage or pleiotropy. We found no relationship between heat and cold tolerances in these populations. Our results show that the thermal niche evolves by direct and indirect selection, in ways that are more complicated than assumed by theoretical models.     

A novel variant in DMXL2 gene is associated with autosomal dominant non-syndromic hearing impairment (DFNA71) in a Cameroonian family

Approximately half of congenital hearing impairment cases are inherited, with non-syndromic hearing impairment (NSHI) being the most frequent clinical entity of genetic hearing impairment cases. A family from Cameroon with NSHI was investigated by performing exome sequencing using DNA samples obtained from three family members, followed by direct Sanger sequencing in additional family members and controls participants. We identified an autosomal dominantly inherited novel missense variant [NM_001174116.2:c.918G>T; p.(Q306H)] in DMXL2 gene (MIM:612186) that co-segregates with mild to profound non-syndromic sensorineural hearing impairment . The p.(Q306H) variant which substitutes a highly conserved glutamine residue is predicted deleterious by various bioinformatics tools and is absent from several genome databases. This variant was also neither found in 121 apparently healthy controls without a family history of hearing impairment , nor 112 sporadic NSHI cases from Cameroon. There is one previous report of a large Han Chinese NSHI family that segregates a missense variant in DMXL2. The present study provides additional evidence that DMXL2 is involved in hearing impairment etiology, and we suggest DMXL2 should be considered in diagnostic hearing impairment panels.     

Structural requirements of the ASBT by 3D-QSAR analysis using aminopyridine conjugates of chenodeoxycholic acid

The human apical sodium-dependent bile acid transporter (ASBT) is a validated drug target and can be employed to increase oral bioavailability of various drug conjugates. The aim of the present study was to investigate the chemical space around the 24-position of bile acids that influences both inhibition and uptake by the transporter. A series of 27 aminopyridine and aminophenol conjugates of glutamyl-chenodeoxycholate were synthesized and their ASBT inhibition and transport kinetics (parametrized as K(i), K(t), and J(max)) measured using stably transfected ASBT-MDCK cells. All conjugates were potent ASBT inhibitors. Monoanionic conjugates exhibited higher inhibition potency than neutral conjugates. However, neutral conjugates and chloro-substituted monoanionic conjugates were not substrates, or at least not apparent substrates. Kinetic analysis of substrates indicated that similar values for K(i) and K(t) implicate substrate binding to ASBT as the rate-limiting step. Using 3D-QSAR, four inhibition models and one transport efficiency model were developed. Steric fields dominated in CoMFA models, whereas hydrophobic fields dominated CoMSIA models. The inhibition models showed that a hydrophobic or bulky substitute on the 2 or 6 position of a 3-aminopyridine ring enhanced activity, while a hydrophobic group on the 5 position was detrimental. Overall, steric and hydrophobic features around the 24 position of the sterol nucleus strongly influenced bile acid conjugate interaction with ASBT. The relative location of the pyridine nitrogen and substituent groups also modulated binding.     

Metagenomic study of single-nucleotide polymorphism within candidate genes associated with type 2 diabetes in an Indian population

A population-based study was undertaken to evaluate linkage between single-nucleotide polymorphisms known as risk factors and type 2 diabetes in an Indian population. The study population was comprised of 40 normal glucose-tolerant individuals (21 males and 19 females) and 40 type 2 diabetes patients (21 males and 19 females). The genes and their corresponding single-nucleotide polymorphisms that we screened were VDR (rs 731236 and rs 1544410), IL-6 (rs 1800795), TCF7L2 (rs 7903146) and TNF-α (rs 1800629). The risk alleles were more frequent in the subjects with type 2 diabetes, except for the TNF-α gene, which was very infrequent in the population; the normal allele occurred at high and similar frequencies in both normal and diabetic individuals.