mab-7 encodes a novel transmembrane protein that orchestrates sensory ray morphogenesis in C. elegans

The tapered sensory rays of the male Caenorhabditis elegans are important for successful male/hermaphrodite copulation. A group of ram (ray morphology abnormal) genes encoding modifying enzymes and transmembrane protein have been reported as key regulators controlling ray morphogenesis. Here we report the characterization of another component essential for this morphogenetic process encoded by mab-7. This gene is active in the hypodermis, structural cells, the body seam and several head neurons. It encodes a novel protein with a hydrophobic region at the N-terminus, an EGF-like motif, an ShKT motif and a long C-terminal tail. All these domains are shown to be critical to MAB-7 activity except the EGF-like domain, which appears to be regulatory and dispensable. MAB-7 is shown to be a type II membrane protein, tethered on the cell surface by the N-terminal transmembrane domain with the remainder of the protein exposed to the extracellular matrix. Since ectopic mab-7 expression in any ray cell or even in touch neurons of non-ray lineage can rescue the mutant phenotype, mab-7 is probably acting non-autonomously. It may facilitate intercellular communication among ray cells to augment normal ray morphogenesis.     

The pleiohomeotic gene is required for maintaining expression of genes functioning in ventral appendage formation in Drosophila melanogaster

Polycomb group (PcG) proteins are negative regulators that maintain the expression of homeotic genes and affect cell proliferation. Pleiohomeotic (Pho) is a unique PcG member with a DNA-binding zinc finger motif and was proposed to recruit other PcG proteins to form a complex. The pho null mutants exhibited several mutant phenotypes such as the transformation of antennae to mesothoracic legs. We examined the effects of pho on the identification of ventral appendages and proximo-distal axis formation during postembryogenesis. In the antennal disc of the pho mutant, Antennapedia (Antp), which is a selector gene in determining leg identity, was ectopically expressed. The homothorax (hth), dachshund (dac) and Distal-less (Dll) genes involved in proximo-distal axis formation were also abnormally expressed in both the antennal and leg discs of the pho mutant. The engrailed (en) gene, which affects the formation of the anterior-posterior axis, was also misexpressed in the anterior compartment of antennal and leg discs. These mutant phenotypes were enhanced in the mutant background of Posterior sex combs (Psc) and pleiohomeotic-like (phol), which are another PcG genes. These results suggest that pho functions in maintaining expression of genes involved in the formation of ventral appendages and the proximo-distal axis.     

Identification and characterization of a novel chitinase-like gene cluster (AgCht5) possibly derived from tandem duplications in the African malaria mosquito, Anopheles gambiae

Insect chitinase 5 (Cht5), a well-characterized enzyme found in the molting fluid and/or integument, is classified as a group I chitinase and is usually encoded by a single gene. In this study, a Cht5 gene cluster consisting of five different chitinase-like genes (AgCht5-1, AgCht5-2, AgCht5-3, AgCht5-4 and AgCht5-5) was identified by a bioinformatics search of the genome of Anopheles gambiae. The gene models were confirmed by cloning and sequencing of the corresponding cDNAs and gene expression profiles during insect development were determined. All of these genes are found in a single cluster on chromosome 2R. Their open reading frames (ORF) range from 1227 to 1713 bp capable of encoding putative proteins ranging in size from 409 to 571 amino acids. The identities of their cDNA sequences range from 52 to 66%, and the identities of their deduced amino acid sequences range from 38 to 53%. There are four introns for AgCht5-1, two for AgCht5-2 and AgCht5-3, only one for AgCht5-4, but none for AgCht5-5 in the genome. All five chitinase-like proteins possess a catalytic domain with all of the conserved sequence motifs, but only AgCht5-1 has a chitin-binding domain. Phylogenetic analysis of these deduced proteins along with those from other insect species suggests that AgCht5-1 is orthologous to the Cht5 proteins identified in other insect species. The differences in expression patterns of these genes at different developmental stages further support that these genes may have distinct functions. Additional searching of the genomes of two other mosquito species led to the discovery of four Cht5-like genes in Aedes aegypti and three in Culex quinquefasciatus. Thus, the presence of a Cht5 gene cluster appears to be unique to mosquito species and these genes may have resulted from gene tandem duplications.     

Position dependence of hemiray morphogenesis during tail fin regeneration in Danio rerio

The fins of actinopterygian can regenerate following amputation. Classical papers have shown that the ray, a structural unit of these fins, might regenerate independent of this appendage. Each fin ray is formed by two apposed contralateral hemirays. A hemiray may autonomously regenerate and segmentate in a position-independent manner. This is observed when heterotopically grafted into an interray space, after amputation following extirpation of the contralateral hemiray or when simply ablated. During this process, a proliferating hemiblastema is formed, as shown by bromodeoxyuridine incorporation, from which the complete structure will regenerate. This hemiblastema shows a patterning of gene expression domain similar to half ray blastema. Interactions between contralateral hemiblastema have been studied by recombinant rays composed of hemirays from different origins on the proximo-distal or dorso-ventral axis of the caudal fin. Dye 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocianine perchlorate labeling of grafted tissues was used as tissular marker. Our results suggest both that there are contralateral interactions between hemiblastema of each ray, and that hemiblastema may vary its morphogenesis, always differentiating as their host region. These non-autonomous, position-dependent interactions control coordinated bifurcations, segment joints and ray length independently. A morphological study of the developing and regenerating fin of another long fin mutant zebrafish suggests that contralateral hemiblastema interactions are perturbed in this mutant.     

The genetics of ray pattern variation in <Emphasis Type="Italic">Caenorhabditis briggsae</Emphasis>

Background

How does intraspecific variation relate to macroevolutionary change in morphology? This question can be addressed in species in which derived characters are present but not fixed. In rhabditid nematodes, the arrangement of the nine bilateral pairs of peripheral sense organs (rays) in tails of males is often the most highly divergent character between species. The development of ray pattern involves inputs from hometic gene expression patterns, TGFβ signalling, Wnt signalling, and other genetic pathways. In Caenorhabditis briggsae, strain-specific variation in ray pattern has provided an entrée into the evolution of ray pattern. Some strains were fixed for a derived pattern. Other strains were more plastic and exhibited derived and ancestral patterns at equal frequencies.

Results

Recombinant inbred lines (RILs) constructed from crosses between the variant C. briggsae AF16 and HK104 strains exhibited a wide range of phenotypes including some that were more extreme than either parental strain. Transgressive segregation was significantly associated with allelic variation in the C. briggsae homolog of abdominal B, Cb-egl-5. At least two genes that affected different elements of ray pattern, ray position and ray fusion, were linked to a second gene, mip-1. Consistent with this, the segregation of ray position and ray fusion phenotypes were only partially correlated in the RILs.

Conclusions

The evolution of ray pattern has involved allelic variation at multiple loci. Some of these loci impact the specification of ray identities and simultaneously affect multiple ray pattern elements. Others impact individual characters and are not constrained by covariance with other ray pattern elements. Among the genetic pathways that may be involved in ray pattern evolution is specification of anteroposterior positional information by homeotic genes.

     

Electric organ morphology and function in the lesser electric ray,Narcine brasiliensis

The lesser electric ray, Narcine brasiliensis, is a small, demersal ray capable of generating electricity through its main and accessory electric organs. Although closely related to the large piscivorous torpedo rays, it differs in size, habitat, and prey. Based on these differences, we hypothesized that the main electric organs are used for predator defense rather than feeding and that the accessory electric organs, specific to this species, are used for intraspecific communication. We found that the mass of the main and accessory electric organs were both significantly smaller in females than in males. Whereas the main electro-somatic index does not change with growth, the accessory electro-somatic index increases, providing support for the accessory electric organs’ use in intraspecific communication. We characterized the discharge properties of the main electric organ throughout ontogeny by simulating a predation attempt on the ray. Rays always responded by generating electric organ discharges (EODs) and by flexing the tail dorsoventrally and laterally. The main EOD amplitude, measured directly at the source, increased logarithmically with disc width to a maximum measured amplitude of 56 V. Minimum amplitude was more variable, but followed a positive power relationship with disc width. Neonates produced trains comprised of significantly more EODs than the adults. Over the course of the first set of discharges, all age classes showed a decrease in fundamental frequency and an increase in train duration. In contrast to these defensive responses, the rays did not generate EODs while foraging or feeding on live prey.     

Ray-interray interactions during fin regeneration of Danio rerio

Teleost fin ray bifurcations are characteristic of each ray in each fin of the fishes. Control of the positioning of such morphological markers is not well understood. We present evidence suggesting that the interray blastema is necessary for a proper bifurcation of each ray during regeneration in Danio rerio (Hamilton-Buchanan) (Cyprinidae, Teleostei). We performed single ray ablations, heterotopical graftings of ray fragments and small holes in lateral rays which do not normally bifurcate, to generate recombinants in which the lateral rays are surrounded with ectopic interrays originating from different positions within the tail fin. These ray-interray recombinants do now bifurcate. Furthermore, we show that the interray tissue and surrounding epidermis can modulate the length of the ray. These results stress the role of the interray in inducing bifurcations of the ray blastema as well as modulating ray morphogenesis in general. In addition, gene expression analysis under these experimental conditions suggests that msxA and msxD expression in the ray and interray epidermis is controlled by the ray blastema and that bmp4 could be a candidate signal involved in these inductions.     

THE NERVOUS MECHANISM OF COORDINATION IN THE CRINOID,ANTEDON ROSACEUS

1. Stimulation causes Antedon to swim by means of alternate oral bending and dorsal stroke of the arms. Two arms of a given ray move alternately so that while one is executing the aboral stroke its mate is flexing ventrally. This implies reciprocal inhibition. 2. Recriprocal inhibition between the two arms of an isolated ray can be abolished by the use of either strychnine or nicotine. 3. Coordination between the rays is referable to the conducting properties of the nervous pentagon which connects the five rays. In this system an impulse loses in effectiveness as it passes from the point of origin. 4. When Antedon is made to rest oral face down on the floor of an aquarium, oral flexion of all the rays, swimming movements, and righting result. Antedon is therefore negatively stereotropic with reference to its ventral side. 5. Excitation of the dorsal cirri results in aboral bending of all the rays. Stimulation of the cirri inhibits ventral flexion to the extent of preventing righting movements while on the other hand stimulation of the ventral surface inhibits the grasp reflex of the cirri. Thus oral and aboral sides of Antedon exhibit dynamic symmetry although structurally dissimilar.     

Role of mef2ca in developmental buffering of the zebrafish larval hyoid dermal skeleton

Phenotypic robustness requires a process of developmental buffering that is largely not understood, but which can be disrupted by mutations. Here we show that in mef2ca^b1086 loss of function mutant embryos and early larvae, development of craniofacial hyoid bones, the opercle (Op) and branchiostegal ray (BR), becomes remarkably unstable; the large magnitude of the instability serves as a positive attribute to learn about features of this developmental buffering. The OpBR mutant phenotype variably includes bone expansion and fusion, Op duplication, and BR homeosis. Formation of a novel bone strut, or a bone bridge connecting the Op and BR together occurs frequently. We find no evidence that the phenotypic stability in the wild type is provided by redundancy between mef2ca and its co-ortholog mef2cb, or that it is related to the selector (homeotic) gene function of mef2ca. Changes in dorsal–ventral patterning of the hyoid arch also might not contribute to phenotypic instability in mutants. However, subsequent development of the bone lineage itself, including osteoblast differentiation and morphogenetic outgrowth, shows marked variation. Hence, steps along the developmental trajectory appear differentially sensitive to the loss of buffering, providing focus for the future study.     

Musculoskeletal morphology and regionalization within the dorsal and anal fins of bluegill sunfish (Lepomis macrochirus)

Ray‐finned fishes actively control the shape and orientation of their fins to either generate or resist hydrodynamic forces. Because of the emergent mechanical properties of their segmented, bilaminar fin rays (lepidotrichia), and actuation by multiple muscles, fish can control the rigidity and curvature of individual rays independently, thereby varying the resultant forces across the fin surfaces. Expecting that differences in fin‐ray morphology should reflect variation in their mechanical properties, we measured several musculoskeletal features of individual spines and rays of the dorsal and anal fins of bluegill sunfish, Lepomis macrochirus, and assessed their mobility and flexibility. We separated the fin‐rays into four groups based on the fin (dorsal or anal) or fin‐ray type (spine or ray) and measured the length of the spines/rays and the mass of the three median fin‐ray muscles: the inclinators, erectors and depressors. Within the two ray groups, we measured the portion of the rays that were segmented vs. unsegmented and branched vs. unbranched. For the majority of variables tested, we found that variations between fin‐rays within each group were significantly related to position within the fin and these patterns were conserved between the dorsal and anal rays. Based on positional variations in fin‐ray and muscle parameters, we suggest that anterior and posterior regions of each fin perform different functions when interacting with the surrounding fluid. Specifically, we suggest that the stiffer anterior rays of the soft dorsal and anal fins maintain stability and keep the flow across the fins steady. The posterior rays, which are more flexible with a greater range of motion, fine‐tune their stiffness and orientation, directing the resultant flow to generate lateral and some thrust forces, thus acting as an accessory caudal fin. J. Morphol., 2012. © 2011 Wiley Periodicals, Inc.     

The selector gene cut represses a neural cell fate that is specified independently of the Achaete-Scute-Complex and atonal.

The peripheral nervous system (PNS) of Drosophila offers a powerful system to precisely identify individual cells and dissect their genetic pathways of development. The mode of specification of a subset of larval PNS cells, the multiple dendritic (md) neurons (or type II neurons), is complex and still poorly understood. Within the dorsal thoracic and abdominal segments, two md neurons, dbd and dda1, apparently require the proneural gene amos but not atonal (ato) or Achaete-Scute-Complex (ASC) genes. ASC normally acts via the neural selector gene cut to specify appropriate sensory organ identities. Here, we show that dbd- and dda1-type differentiation is suppressed by cut in dorsal ASC-dependent md neurons. Thus, cut is not only required to promote an ASC-dependent mode of differentiation, but also represses an ASC- and ato-independent fate that leads to dbd and dda1 differentiation.     

Retinoic Acid Is Involved in the Metamorphosis of the Anal Fin into an Intromittent Organ,the Gonopodium,in the Green Swordtail (Xiphophorus hellerii)

In poeciliid fish the male anal fin has been transformed into a gonopodium, an intromittent organ required for internal fertilization. Elevated testosterone levels induce metamorphosis of a subset of anal fin rays to grow and form the specialized terminal structures of the gonopodium. The molecular mechanisms underlying these processes are largely unknown. Here, we investigated whether retinoic acid (RA) signaling is involved in gonopodium development in the swordtail Xiphophorus hellerii. We showed that aldh1a2, a RA synthesizing enzyme, and the RA receptors, rar-ga and rar-gb, are expressed in anal fins during metamorphosis. aldh1a2 expression is regulated by testosterone in a concentration-dependent manner and is up-regulated in both hormone-induced and naturally developing gonopodia. Androgen receptor (ar), a putative regulator of gonopodial development, is co-expressed with aldh1a2 and the RA receptors in gonopodial rays. Importantly, experimental increase of RA signaling promoted growth of the gonopodium and increased the number of new segments. Based on gene expression analyses and pharmacological manipulation of gonopodium development, we show that the RA signaling pathway is activated in response to androgen signaling and promotes fin ray growth and development during the metamorphosis of the anal fin into the gonopodium.     

Firefly luciferase genes from the subfamilies Psilocladinae and Ototretinae (Lampyridae, Coleoptera)

Firefly luciferase genes have been isolated from approximately 20 species of Lampyrinae, Luciolinae, and Photurinae. These are mostly nocturnal luminescent species that use light signals for sexual communication. In this study, we isolated three cDNAs for firefly luciferase from Psilocladinae (Cyphonocerus ruficollis) and Ototretinae (Drilaster axillaris and Stenocladius azumai), which are diurnal non-luminescent or weakly luminescent species that may use pheromones for communication. The amino acid sequences deduced from the three cDNAs showed 81-89% identities to each other and 60-81% identities with known firefly luciferases. The three purified recombinant proteins showed luminescence and fatty acyl-CoA synthetic activities, as observed in other firefly luciferases. The emission maxima by the three firefly luciferases (λmax, 545-546 nm) were shorter than those by known luciferases from the nocturnal fireflies (λmax, 550-568 nm). These results suggest that the primary structures and enzymatic properties of luciferases are conserved in Lampyridae, but the luminescence colors were red-shifted in nocturnal species compared to diurnal species.     

Comparative analysis of malate synthase G from Mycobacterium tuberculosis and E. coli: role of ionic interaction in modulation of structural and functional properties

Metabolic plasticity of Mycobacterium renders high degree of adaptive advantages in the persistence through the upregulation of glyoxylate shunt. The malate synthase (MS), an important enzyme of the shunt belongs to the G isoform and expressed predominantly as monomer. Here we did a comparative unfolding studies of two homologous MS from Mycobacterium tuberculosis (MtbMS) and Escherichia coli (ecMS) using various biophysical techniques. Despite having high sequence identities, they show different structural, stability and functional properties. The study suggests that the differences in the stability and unfolding of the two enzymes are by virtue of differential electrostatic modulation unique to their respective molecular assembly.     

Neuronal Cell Fate Specification by the Convergence of Different Spatiotemporal Cues on a Common Terminal Selector Cascade

Specification of the myriad of unique neuronal subtypes found in the nervous system depends upon spatiotemporal cues and terminal selector gene cascades, often acting in sequential combinatorial codes to determine final cell fate. However, a specific neuronal cell subtype can often be generated in different parts of the nervous system and at different stages, indicating that different spatiotemporal cues can converge on the same terminal selectors to thereby generate a similar cell fate. However, the regulatory mechanisms underlying such convergence are poorly understood. The Nplp1 neuropeptide neurons in the Drosophila ventral nerve cord can be subdivided into the thoracic-ventral Tv1 neurons and the dorsal-medial dAp neurons. The activation of Nplp1 in Tv1 and dAp neurons depends upon the same terminal selector cascade: col>ap/eya>dimm>Nplp1. However, Tv1 and dAp neurons are generated by different neural progenitors (neuroblasts) with different spatiotemporal appearance. Here, we find that the same terminal selector cascade is triggered by Kr/pdm>grn in dAp neurons, but by Antp/hth/exd/lbe/cas in Tv1 neurons. Hence, two different spatiotemporal combinations can funnel into a common downstream terminal selector cascade to determine a highly related cell fate.