Neural crest contribution to the avian shoulder girdle and implications to girdle evolution in vertebrates

Neural crest (NC) is an established source for many endochondral and intramembranous bones in the skull and postcranial skeleton in vertebrates. Neural crest cells also contribute to the trapezius/cleidohyoideus muscle attachment sites on the shoulder girdle of the mouse, where they are found in the scapula, clavicle, and sternum. In the avian shoulder girdle, NC cells from the level of the first two cranial−most somites were only found so far in the clavicle, while in the axolotl, the NC contribution to the shoulder girdle was not found at all. In this study we aimed to determine whether NC cells caudal to the level of the second somite contribute to the cartilaginous shoulder girdle in birds and to analyse the phylogenetic distribution of NC cells in the vertebrate shoulder girdle. Homotopic quail to chick embryos and GFP+ to wild type chick embryos transplantations of the neural tube including presumptive NC, as well as immunohistochemical detection of NC markers, such as HNK-1 and PDGFRα revealed no contribution of NC cells from somite levels 3−27 to the skeletal elements of the shoulder girdle, including, but not restricting to muscle attachment sites, despite abundance of other NC derivatives. Thus, in birds, NC does not contribute to the formation of the cartilaginous shoulder girdle. The negative result is discussed in a broad evolutionary aspect. It supports the notion of the uniqueness of NC contribution to the variety of endochondral bones in mice (or mammals). In other vertebrates, including birds, only the cells of the cranial NC seem to migrate to the shoulder girdle and contribute to the intramembranous clavicles and/or interclavicle. We critically evaluate the existing hypotheses on evolution of NC contribution to the shoulder girdle in vertebrates

The development and origins of vertebrate meninges

Meninges comprise three distinct layers, the dura mater, arachnoid, and pia mater that surround the brain, spinal cord and some parts of the nerves. Traditionally the meninges were believed to serve only as protection for tissues that they encase. However recent work shows they have other important functions related to development and regulation of the nervous system. Given the importance of the meninges, it is surprising that we know very little about their development. The embryological origin of the meninges has been debated for over a hundred years. Some studies imply that the meninges develop from the neural crest, while others suggest that they come from the somites. Here, we investigated the temporal development of meninges in birds and mice and found they form at comparable stages. We investigated the origin of avian spinal meninges using chick/quail cell tracing protocols and found they do not develop from the somites as previously thought. We propose that meningeal epithelial blood vessels may have been mistaken as meninges and led to an erroneous conclusion by previous investigators. We present data that show that avian spinal meninges originated from the neural crest supported by data demonstrating that they express the neural crest marker HNK1. Finally using the Wnt1-Cre mouse we show that trunk meninges of mammals also originate from neural crest

The occipital lateral plate mesoderm is a novel source for vertebrate neck musculature

In vertebrates, body musculature originates from somites, whereas head muscles originate from the cranial mesoderm. Neck muscles are located in the transition between these regions. We show that the chick occipital lateral plate mesoderm has myogenic capacity and gives rise to large muscles located in the neck and thorax. We present molecular and genetic evidence to show that these muscles not only have a unique origin, but additionally display a distinct temporal development, forming later than any other muscle group described to date. We further report that these muscles, found in the body of the animal, develop like head musculature rather than deploying the programme used by the trunk muscles. Using mouse genetics we reveal that these muscles are formed in trunk muscle mutants but are absent in head muscle mutants. In concordance with this conclusion, their connective tissue is neural crest in origin. Finally, we provide evidence that the mechanism by which these neck muscles develop is conserved in vertebrates

The hypaxial origin of the epaxially located rhomboid muscles

In vertebrates, skeletal muscles of the body are made up of epaxial and hypaxial muscles based on their innervation and relative position to the vertebral column. The epaxial muscles are innervated by the dorsal branches of the spinal nerves and comprise the intrinsic (deep) back muscles, while the hypaxial muscles are innervated by the ventral branches of the spinal nerves including the plexus and consist of a heterogeneous group of intercostal, abdominal, and limb as well as girdle muscles. The canonical view holds that the epaxial muscles are derived from the medial halves of the somites, whereas the hypaxial muscles are all derived from the lateral somitic halves. The rhomboid muscles are situated dorsal to the vertebral column and therefore in the domain typically occupied by epaxial muscles. However, they are innervated by a ventral branch of the brachial plexus called the N. dorsalis scapulae. Due to the apparent inappropriate position of the muscle in relation to its innervation we investigated its origin to help clarify this issue. To study the embryonic origin of the rhomboid muscles, we followed derivatives of the medial and lateral somite halves using quail-chick chimeras. Our results showed that the rhomboid muscles are made up of cells derived mainly from the lateral portion of the somite. Therefore the rhomboid muscles which lie within the epaxial domain of the body, originate from the hypaxial domain of the somites. However, their connective tissue is derived from both medial and lateral somite

Characterisation of development and electrophysiological mechanisms underlying rhythmicity of the avian lymph heart

Despite significant advances in tissue engineering such as the use of scaffolds, bioreactors and pluripotent stem cells, effective cardiac tissue engineering for therapeutic purposes has remained a largely intractable challenge. For this area to capitalise on such advances, a novel approach may be to unravel the physiological mechanisms underlying the development of tissues that exhibit rhythmic contraction yet do not originate from the cardiac lineage. Considerable attention has been focused on the physiology of the avian lymph heart, a discrete organ with skeletal muscle origins yet which displays pacemaker properties normally only found in the heart. A functional lymph heart is essential for avian survival and growth in ovo. The histological nature of the lymph heart is similar to skeletal muscle although molecular and bioelectrical characterisation during development to assess mechanisms that contribute towards lymph heart contractile rhythmicity have not been undertaken. A better understanding of these processes may provide exploitable insights for therapeutic rhythmically contractile tissue engineering approaches in this area of significant unmet clinical need. Here, using molecular and electrophysiological approaches, we describe the molecular development of the lymph heart to understand how this skeletal muscle becomes fully functional during discrete in ovo stages of development. Our results show that the lymph heart does not follow the normal transitional programme of myogenesis as documented in most skeletal muscle, but instead develops through a concurrent programme of precursor expansion, commitment to myogenesis and functional differentiation which offers a mechanistic explanation for its rapid development. Extracellular electrophysiological field potential recordings revealed that the peak-to-peak amplitude of electrically evoked local field potentials elicited from isolated lymph heart were significantly reduced by treatment with carbachol; an effect that could be fully reversed by atropine. Moreover, nifedipine and cyclopiazonic acid both significantly reduced peak-to-peak local field potential amplitude. Optical recordings of lymph heart showed that the organ’s rhythmicity can be blocked by the HCN channel blocker, ZD7288; an effect also associated with a significant reduction in peak-to-peak local field potential amplitude. Additionally, we also show that isoforms of HCN channels are expressed in avian lymph heart. These results demonstrate that cholinergic signalling and L-type Ca2+ channels are important in excitation and contraction coupling, while HCN channels contribute to maintenance of lymph heart rhythmicity

Analytical fluid film force calculation in the case of short bearing with a fully developed turbulent flow

The main purpose of this paper is to define a methodology to determine the analytical approximate closed-form expression of non-steady fluid film force and of the oil film coefficients for the liquid-lubricated journal bearings in the case of a fully developed turbulent flow regime. The considered model is a symmetrical rigid rotor supported on two lubricated journal bearings; this paper considers the cases of the short bearing approximation, introducing the turbulence correction flow factors in the classical Reynolds equation. The proposed methodology gives the opportunity to solve in approximate way the equation governing the distribution of pressure in the bearing oil gap and then to obtain the closed- form expressions for the non-steady fluid forces. This approach shows the benefit of minimising the calculation time required for the non-linear dynamic analysis of rotors on turbulent journal bearings without any significant loss of accuracy giving a better readability of the parameter involved on the system behaviour

On the tribological performance of vegetal lubricants: experimental investigation on Jatropha Curcas L. oil

The limited resources of petroleum-based lubricants and increased environmental contamination, that they produce, lead to increased demand for bio-lubricants. Due to several factors such as biodegradability, good lubricating properties and low production costs, the plant oils represent a good alternative as reference to replace the petroleum-based oils. Obviously, the need to ensure the use of vegetable oils as a source of food makes non-edible vegetable oils a formidable source for plant oil lubricants. Thus, the toxicity of Jatropha Curcas L. oil makes it a very attractive and alternative lubricant source. Therefore, the aim of this work is to investigate on tribological performance of Jatropha Curcas L. oil in the lubricating contact pair AISI 52100 steel sliding against X210Cr12 steel. The experimental tests were carried out using ball-on-flat reciprocatory tribometer for several frequencies and with normal load of 12N. The Jatropha Curcas L. oil was analyzed for its chemical and physical properties such as viscosity, density and flash point. The results were interpreted on the basis of the evolution of the friction coefficient. The evolution of the friction coefficient was monitored for 40 min in all tests. The results show that the friction coefficient decreases with the increase of the frequency, and the final value stays in the range of 0.04-0.122

Effect of Fiber Orientation on the Tribological Performance of Abaca-Reinforced Epoxy Composite under Dry Contact Conditions

This paper presents tribological research of an abaca fiber-reinforced epoxy composite material, analyzing fiber orientation and its effect on the tribological performances of the composite. The extremely low viscosity epoxy resin reinforced with NaOH-treated long abaca fibers is investi- gated under the different operating conditions. The unidirectional abaca fibers reinforced the epoxy resin and formed composite specimens with fibers in three directions, parallel (P-O), anti-parallel (AP-O) and normal (N-O), while keeping the sliding direction. The specimens were fabricated using fiber volume fractions of 10 vol%, 20 vol% and 30 vol% using the vacuum infusion technique. The block-on-disc (BOD) apparatus has been used to exhibit the tribological tests. Normal loads of 35 N and 45 N have been used for testing purposes. The experimental results indicated that the presence of abaca fiber significantly improved the wear characteristics of the matrix. An increased coefficient of friction was observed in samples with anti-parallel-oriented fibers at an applied load of 35 N. The conducted research shows that the use of abaca fibers as fillers could improve the tribological characteristics of the epoxy resin-based composite material

ENGINEERING FOR RURAL DEVELOPMENT EXPERIMENTAL CHARACTERIZATION OF DEGRADATION OF REACTIVE RESIN FILLED WITH ORGANIC MICROPARTICLES

Abstract. Composite materials rank among the structural materials with a highly promising trend. The main advantage of composite materials is the synergistic effect of the individual sub-components of the system, which allows great adaptation of these materials and excellent mechanical properties. In recent years, the substitution of inorganic materials with organic materials is increasingly used in the field of composite systems. From the materials engineering point of view, this substitution makes use of very interesting properties of natural fillers. These materials are environmentally friendly and their prices are usually lower than similar synthetic fillers. However, it is also necessary to mention the negative side of organic fillers and that is their natural character. Natural fillers are so different from one another and evince greater variance than the observed values of synthetic materials. In terms of long-term applications, the degradation of natural materials can rank among limits. Natural particulate fillers can be utilized in interaction with reactive resins; they can reduce the final price while maintaining the adhesive characteristics. This paper describes the adhesive characteristics of reaction resins filled with microparticles prepared from pomace seeds of Phoenix dactylifera and it also describes the degradation of these materials. A climatic chamber was used for this experiment. Describing the degradation processes it is important to define application areas. Electron microscopy was used when evaluating the failure of bonded joints. The degradation corresponding to 35 cycles resulted in a 37 % decrease in shear strength. Keywords: composite system, mechanical properties, Phoenix dactylifera, SEM. Introduction Composite materials are materials that combine mechanical and physical properties of their subphases, currently, the composite systems are widely used in industries due to their flexible properties [1; 2]. Particulate fillers in polymer materials are used primarily to increase the hardness, abrasion resistance or optimize the tensile characteristics [3; 4]. The presence of particles leads to optimize the shear strength while reducing the prices of the resulting joint in the area of bonded joints. Currently, the synthetic materials are increasingly replaced with natural ones. The natural fibers and particles are used in the composite systems. The particles based on wood (e.g., wood flour, flour made from bamboo) or biomass resulting from processing of certain species of plants and their fruit (Jatropha curcas) can be used as a filler for composite systems [5; 6]. Natural particles minimize the cost and optimize certain mechanical characteristics Degradation of polymers in terms of application and product lifecycle is a very important factor. Degradation can be characterized as an undesirable change of properties over time; this change is primarily associated with changes in molecular weight and structure of the material. [9] The factors causing degradation of polymeric materials can include temperature, humidity, and also the action of microorganisms. Adhesive bonds based on the composite, where the matrix is epoxy resin, are often exposed to various degradation effects The aim of the experiment was to describe the degradation process -shear strength changes -of adhesive bonds formed by the composite system based on natural particles prepared from the biomass formed during the processing of fruits (dates) from Phoenix dactylifera plant and epoxy resins. Thus obtained biomass could be considered as biological waste, ecological use of which from the point of economic and environmental view is desirable. The experiment thus describes degradation of materials sensitive to the environment, the production of which is inexpensive