Eph:ephrin-B1 forward signaling controls fasciculation of sensory and motor axons

Axon fasciculation is one of the processes controlling topographic innervation during embryonic development. While axon guidance steers extending axons in the accurate direction, axon fasciculation allows sets of co-extending axons to grow in tight bundles. The Eph:ephrin family has been involved both in axon guidance and fasciculation, yet it remains unclear how these two distinct types of responses are elicited. Herein we have characterized the role of ephrin-B1, a member of the ephrinB family in sensory and motor innervation of the limb. We show that ephrin-B1 is expressed in sensory axons and in the limb bud mesenchyme while EphB2 is expressed in motor and sensory axons. Loss of ephrin-B1 had no impact on the accurate dorso-ventral innervation of the limb by motor axons, yet EfnB1 mutants exhibited decreased fasciculation of peripheral motor and sensory nerves. Using tissue-specific excision of EfnB1 and in vitro experiments, we demonstrate that ephrin-B1 controls fasciculation of axons via a surround repulsion mechanism involving growth cone collapse of EphB2-expressing axons. Altogether, our results highlight the complex role of Eph:ephrin signaling in the development of the sensory-motor circuit innervating the limb.     

MHC‐disassortative mate choice and inbreeding avoidance in a solitary primate

Sexual selection theory suggests that choice for partners carrying dissimilar genes at the major histocompatibility complex (MHC) may play a role in maintaining genetic variation in animal populations by limiting inbreeding or improving the immunity of future offspring. However, it is often difficult to establish whether the observed MHC dissimilarity among mates drives mate choice or represents a by‐product of inbreeding avoidance based on MHC‐independent cues. Here, we used 454‐sequencing and a 10‐year study of wild grey mouse lemurs (Microcebus murinus), small, solitary primates from western Madagascar, to compare the relative importance on the mate choice of two MHC class II genes, DRB and DQB, that are equally variable but display contrasting patterns of selection at the molecular level, with DRB under stronger diversifying selection. We further assessed the effect of the genetic relatedness and of the spatial distance among candidate mates on the detection of MHC‐dependent mate choice. Our results reveal inbreeding avoidance, along with disassortative mate choice at DRB, but not at DQB. DRB‐disassortative mate choice remains detectable after excluding all related dyads (characterized by a relatedness coefficient r > 0), but varies slightly with the spatial distance among candidate mates. These findings suggest that the observed deviations from random mate choice at MHC are driven by functionally important MHC genes (like DRB) rather than passively resulting from inbreeding avoidance and further emphasize the need for taking into account the spatial and genetic structure of the population in correlative tests of MHC‐dependent mate choice.     

Fish oil supplementation for two generations increases insulin sensitivity in rats

We investigated the effect of fish oil supplementation for two consecutive generations on insulin sensitivity in rats. After the nursing period (21 days), female rats from the same prole were divided into two groups: (a) control group and (b) fish oil group. Female rats were supplemented with water (control) or fish oil at 1 g/kg body weight as a single bolus for 3 months. After this period, female rats were mated with male Wistar rats fed on a balanced chow diet (not supplemented). Female rats continued to receive supplementation throughout gestation and lactation periods. The same treatment was performed for the next two generations (G1 and G2). At 75 days of age, male offspring from G1 and G2 generations from both groups were used in the experiments. G1 rats did not present any difference with control rats. However, G2 rats presented reduction in glycemia and lipidemia and improvement in in vivo insulin sensitivity (model assessment of insulin resistance, insulin tolerance test) as well as in vitro insulin sensitivity in soleus muscle (glucose uptake and metabolism). This effect was associated with increased insulin-stimulated p38 MAP kinase phosphorylation and lower n-6/n-3 fatty acid ratio, but not with activation of proteins from insulin signaling (IR, IRS-1 and Akt). Global DNA methylation was decreased in liver but not in soleus muscle. These results suggest that long-term fish oil supplementation improves insulin sensitivity in association with increased insulin-stimulated p38 activation and decreased n-6:n-3 ratio in skeletal muscle and decreased global DNA methylation in liver.     

A forceful upper jaw facilitates picking-based prey capture: biomechanics of feeding in a butterflyfish,Chaetodon trichrous

Biomechanical models of feeding mechanisms elucidate how animals capture food in the wild, which, in turn, expands our understanding of their fundamental trophic niche. However, little attention has been given to modeling the protrusible upper jaw apparatus that characterizes many teleost species. We expanded existing biomechanical models to include upper jaw forces using a generalist butterflyfish, Chaetodon trichrous (Chaetodontidae) that produces substantial upper jaw protrusion when feeding on midwater and benthic prey. Laboratory feeding trials for C. trichrous were recorded using high-speed digital imaging; from these sequences we quantified feeding performance parameters to use as inputs for the biomechanical model. According to the model outputs, the upper jaw makes a substantial contribution to the overall forces produced during mouth closing in C. trichrous. Thus, biomechanical models that only consider lower jaw closing forces will underestimate total bite force for this and likely other teleost species. We also quantified and subsequently modeled feeding events for C. trichrous consuming prey from the water column versus picking attached prey from the substrate to investigate whether there is a functional trade-off between prey capture modes. We found that individuals of C. trichrous alter their feeding behavior when consuming different prey types by changing the timing and magnitude of upper and lower jaw movements and that this behavioral modification will affect the forces produced by the jaws during prey capture by dynamically altering the lever mechanics of the jaws. In fact, the slower, lower magnitude movements produced during picking-based prey capture should produce a more forceful bite, which will facilitate feeding on benthic attached prey items, such as corals. Similarities between butterflyfishes and other teleost lineages that also employ picking-based prey capture suggest that a suite of key behavioral and morphological innovations enhances feeding success for benthic attached prey items.     

Cellulase Production in Semisolid Cultures of Trichoderma viride

Cellulase was produced by Trichoderma viride in semisolid cultures of rice bran, rice straw and rice hulls. T. viride QM 9414 generally produced higher cellulolytic activity on CM-cellulose (C_x activity) using rice bran-rice hull mixture (2:1 w/w) as substrate compared to strains ITCC 1433 and D 4014. It showed higher C_x activity on rice bran-rice straw mixtures than on rice bran-rice hull mixtures. Maximal extraction of the enzyme from mold bran was obtained with 0.05 m sodium citrate buffer, pH 3.5.