Pharyngeal jaw morphology and homology in Sicydiine Gobies (Teleostei: Gobiidae) and allies

An extremely large number of fifth ceratobranchial teeth, with highly modified, striated, and hooked tips were observed in the central and western Pacific sicydiine goby genus Stiphodon.A scanning electron microscopic study of the form and arrangement of fifth ceratobranchial teeth was conducted to assess the distribution of these modifications in sicydiine gobies and their putative close relatives. Our goals were to explore a new set of characters in gobioid systematics, to test sicydiine monophyly, and to test hypotheses of relationships of sicydiine gobies. Sicydiines are hypothesized herein to be most closely related to the western Pacific Tukugobius and Rhinogobius,freshwater genera with which they share thickened pelvic-fin rays, no teeth on the anterior portion of the fifth ceratobranchial bones, fifth ceratobranchial teeth with differentiated and striated tips, and overlapping anterior rami of the fifth ceratobranchial bones. The latter two characters occur in some, but not all, sicydiines. The pantropical freshwater goby Awaous,often classified with sicydiines, is not considered the closest relative of the subfamily. The highly modified fifth ceratobranchials of Stiphodon are similar to, and concluded here to be homoplasious with, those of the mudflat-dwelling New World goby Evorthodus and the Indo-west Pacific oxudercine gobies, represented in this study by Pseudapocryptes. J. Morphol. 237:257–274, 1998. Published 1998 Wiley-Liss, Inc.     

A peroxiredoxin specifically expressed in two types of pharyngeal neurons is required for normal growth and egg production in Caenorhabditis elegans

A family of antioxidant proteins, the peroxiredoxins, serve two purposes, detoxification of reactive oxygen species and cellular signaling. Among the three peroxiredoxins of Caenorhabditis elegans (CePrx1-3), CePrx2 was found to have a very unusual expression pattern, restricted to only two types of pharyngeal neurons; namely, the single pharyngeal interneuron I4 and the sensory interneuron I2. CePrx1 and CePrx3-depleted worms showed no obvious phenotypic alterations, whereas worms devoid of CePrx2 were retarded developmentally and had a significantly reduced brood size. Other features, such as lifespan, pharyngeal activity or defecation rates were indistinguishable from those of wild-type worms. Recombinant CePrx2 revealed antioxidant activity, as it was able to detoxify hydrogen peroxide and butylhydroperoxide (t-BOOH), and to protect glutamine synthetase from inactivation by thiol-dependent metal-catalyzed oxidation. In addition, the molecule was able to act as a terminal peroxidase in the thioredoxin system. Expression of ceprx2 in C.elegans was induced after short-term exposure of worms to t-BOOH but survival of ceprx2 knockout mutants in the presence of reactive oxygen or nitrogen species was not impaired. Thus, CePrx2 may protect specifically the two types of neurons from oxidative damage or, more likely, plays a critical role in peroxide signaling in this nematode.     

Tyramine receptor (SER-2) isoforms are involved in the regulation of pharyngeal pumping and foraging behavior in Caenorhabditis elegans

Octopamine regulates essential processes in nematodes; however, little is known about the physiological role of its precursor, tyramine. In the present study, we have characterized alternatively spliced Caenorhabditis elegans tyramine receptor isoforms (SER-2 and SER-2A) that differ by 23 amino acids within the mid-region of the third intracellular loop. Membranes prepared from cells expressing either SER-2 or SER-2A bind [3H]lysergic acid diethylamide (LSD) in the low nanomolar range and exhibit highest affinity for tyramine. Similarly, both isoforms exhibit nearly identical Ki values for a number of antagonists. In contrast, SER-2A exhibits a significantly lower affinity than SER-2 for other physiologically relevant biogenic amines, including octopamine. Pertussis toxin treatment reduces affinity for both tyramine and octopamine, especially for octopamine in membranes from cells expressing SER-2, suggesting that the conformation of the mid-region of the third intracellular loop is dictated by G-protein interactions and is responsible for the differential tyramine/octopamine affinities of the two isoforms. Tyramine reduces forskolin-stimulated cAMP levels in HEK293 cells expressing either isoform with nearly identical IC50 values. Tyramine, but not octopamine, also elevates Ca2+ levels in cells expressing SER-2 and to a lesser extent SER-2A. Most importantly, ser-2 null mutants (pk1357) fail to suppress head movements while reversing in response to nose-touch, suggesting a role for SER-2 in the regulation of foraging behavior, and fail to respond to tyramine in assays measuring serotonin-dependent pharyngeal pumping. These are the first reported functions for SER-2. These results suggest that C. elegans contains tyramine receptors, that individual SER-2 isoforms may differ significantly in their sensitivity to other physiologically relevant biogenic amines, such as octopamine (OA), and that tyraminergic signaling may be important in the regulation of key processes in nematodes.     

Morphology of the pharyngeal cavity, especially the surface ultrastructure of gill arches and gill rakers in relation to the feeding ecology of the catfish Rita rita (Siluriformes, Bagridae)

Gill arches and the gill rakers of a sluggish, carnivorous catfish, Rita rita, show significant differences of their surface ultrastructure, which are recognized adaptive modifications in relation to food and feeding ecology of fish. Gill rakers on the first and second pairs of gill arches are borne on the oral side and are long and stout at the epi-ceratobranchial union. Gill rakers on the third and fourth pairs of gill arches, in contrast, are borne on the oral and aboral sides and are relatively delicate and short. Long and stout gill rakers on the first and second pairs of gill arches are considered primarily to prevent entry of undesirably large food items into the pharynx. Two types of taste buds, Type I and Type II, occur on the gill arches and the gill rakers. The raised taste buds, located at the apical ends of the gill rakers on the third, fourth, and the fifth pairs of gill arches could increase gustatory efficiency in the pharynx. Differences in the distribution of taste buds on the pharyngeal sides of different gill arches indicate that the posterior part of the pharynx plays a more crucial role in gustation than does the anterior part. Co-occurrence of teeth and taste buds on the epi- and hypopharyngeal bones denotes that food processing and gustation occur simultaneously in the pharynx. Villiform and caniform teeth on the epi- and hypopharyngeal bones are associated with a complex food-processing cycle. Mucous secretions, oozing through mucous cell openings, provide lubrication facilitating smooth passage of food through the pharynx. The angle of curvature at the epi-ceratobranchial union of the first to fourth pairs of gill arches could assist the ventral drag of ceratobranchials in lowering of the pharyngeal floor, thus resulting in a great expansion of the pharynx, as needed to accommodate the large quantities of food captured.     

The role of neural crest during cardiac development in a mouse model of DiGeorge syndrome

The velo-cardio-facial syndrome (VCFS)/DiGeorge syndrome (DGS) is a genetic disorder characterized by phenotypic abnormalities of the derivatives of the pharyngeal arches, including cardiac outflow tract defects. Neural crest cells play a major role in the development of the pharyngeal arches, and defects in these cells are likely responsible for the syndrome. Most patients are hemizygous for a 1.5- to 3.0-Mb region of 22q11, that is suspected to be critical for normal pharyngeal arch development. Mice hemizygous for a 1.5-Mb homologous region of chromosome 16 (Lgdel/+) exhibit conotruncal cardiac defects similar to those seen in affected VCFS/DGS patients. To investigate the role of Lgdel genes in neural crest development, we fate mapped neural crest cells in Lgdel/+ mice and we performed hemizygous neural crest-specific inactivation of Lgdel. Hemizygosity of the Lgdel region does not eliminate cardiac neural crest migration to the forming aortic arches. However, neural crest cells do not differentiate appropriately into smooth muscle in both fourth and sixth aortic arches and the affected aortic arch segments develop abnormally. Tissue-specific hemizygous inactivation of Lgdel genes in neural crest results in normal cardiovascular development. Based on our studies, we propose that Lgdel genes are required for the expression of soluble signals that regulate neural crest cell differentiation.     

African lungfish genome sheds light on the vertebrate water-to-land transition

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Impact of micro and macroporous TFF membranes on product sieving and chromatography loading for perfusion cell culture

Bioprocess intensification can be achieved through high cell density perfusion cell culture with continuous protein capture integration. Protein passage and cell retention are commonly accomplished using tangential flow filtration systems consisting of microporous membranes. Significant challenges, including low efficiency and decaying product sieving over time, are commonly observed in these cell retention devices. Here, we demonstrate that a macroporous membrane overcomes the product sieving challenges when comparing to several other membrane chemistries and pore sizes within the microporous range. This way, variable chromatography column loading is avoided. The macroporous membrane yielded a 13,000 L/m² volumetric throughput. The membrane's cut-off size results in an increased permeate turbidity due to particles passage, such as cell debris, through pores ranging from 1 to 4 µm. In addition, successful chromatography column plugging mitigation was achieved by employing depth filtration before the chromatographic step. Depth filtration volumetric throughputs were between 600 and 1,000 L/m². Combing a macroporous cell retention device with a depth filter not only provided an alternative to address the challenge of undesired long protein residence times in the bioreactor due to product sieving decay, but also exhibited a throughput increase, making the integration of multicolumn capture chromatography with a perfusion cell culture a more robust process.     

Introgressive hybridization in a trophically polymorphic cichlid

Trophically polymorphic species could represent lineages that are rapidly diverging along an ecological axis or could phenotypically mark the collapse of species through introgressive hybridization. We investigated patterns of introgression between the trophically polymorphic cichlid fish Herichthys minckleyi and its relative H. cyanoguttatus using a combination of population genetics and species tree analyses. We first examined the distribution of mitochondrial haplotypes within the alternative H. minckleyi pharyngeal jaw morphotypes that are endemic to the small desert valley of Cuatro Ciénegas. We recovered two clusters of mitochondrial haplotypes. The first contained a number of slightly differentiated cytochrome b (cytb) haplotypes that showed some phylogeographic signal and were present in both jaw morphotypes. The other haplotype was monomorphic, highly differentiated from the other cluster, present in equal frequencies in the morphotypes, and identical to H. cyanoguttatus haplotypes found outside Cuatro Ciénegas. Then, we investigated whether H. minckleyi individuals with the H. cyanoguttatus cytb were more evolutionarily similar to H. cyanoguttatus or other H. minckleyi using a species tree analysis of 84 nuclear loci. Both H. minckleyi pharyngeal morphotypes, regardless of their cytb haplotype, were quite distinct from H. cyanoguttatus. However, hybridization could be blurring subdivision within H. minckleyi as the alternative jaw morphotypes were not genetically distinct from one another. Accounting for introgression from H. cyanoguttatus will be essential to understand the evolution of the trophically polymorphic cichlid H. minckleyi.     

Scaleable downstream recovery of nematodes used as biopesticides.

This study assesses the suitability of sieving as a scaleable technique for the separation of adult nematodes from infective juveniles, the latter is an effective bioinsecticide whereas the former is waste material resulting from the fermentation process. Batch and semibatch experiments using conventional flow-assisted wet sieving and a novel cross-flow sieving technique were used to study the separation of juveniles from adult nematodes. The experiments were carried out using small-scale devices and the data were analyzed in terms of the screen effectiveness factor. The results were used to identify the sieve size and operating conditions for optimum juvenile recovery. It was found that, for a given species of nematode, optimum recovery was achieved when sieving was carried out in the cross-flow mode, the maximum recovery being a function of the size of the screen. Industrial-scale self-cleaning equipment capable of large-scale continuous screening was used to confirm the capacity of the small-scale operation for scale-up. Experimental results with this unit showed that in continuous operation sieving time is an additional parameter that influences separation performance.     

Microscopic anatomy of pycnogonida: II. Digestive system. III. Excretory system

The digestive system of several species of sea spiders (Pycnogonida, Arthropoda) was studied by electron microscopy. It is composed of the foregut inside a long proboscis, a midgut and a hindgut. Lips near the three jaws at the tip of the proboscis receive several hundred ductules originating from salivary glands. These previously undetected glands open on the lips, a fluted, projecting ridge at the external hinge line of the jaws, i.e., to the outside of the mouth. This disposition suggests affinities to the chelicerate line. The trigonal esophagus within the proboscis contains a complex, setose filter device, operated by dedicated muscles, that serves to reduce ingested food to subcellular dimensions. The midgut has diverticula into the bases of all legs. Its cells differentiate from the basal layer and contain a bewildering array of secretion droplets, lysosomes and phagosomes. In the absence of a hepatopancreas, the midgut serves both digestive and absorptive functions. The cuticle-lined hindgut lies in the highly reduced, peg-like abdomen. Traditionally, pycnogonids have been claimed to have no excretory organ at all. Such a structure, however, has been located in at least one ammotheid, Nymphopsis spinosissima, in which a simple, but standard, excretory gland has been found in the scape of the chelifore. It consists of an end sac, a straight proximal tubule, a short distal tubule, and a raised nephropore. The end sac is a thin-walled and polygonal chamber, about 150 microm in cross section, suspended in the hemocoel of the appendage, its edges radially tethered to the cuticle at more than half a dozen locations. This wall consists of a filtration basement membrane, 1-4 microm thick, facing the hemocoel, and internally of a continuous carpet of podocytes and their pedicels. The podocytes, measuring maximally 10 by 15 microm, have complex contents, of which a labyrinthine system of connected intracellular channels stands out. These coated cisternae open into a central vacuole that often rivals the nucleus in size. The design of the organ closely approximates that of the primitive crustacean Hutchinsoniella macracantha.