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Coral bleaching is a major threat to coral reefs worldwide and is predicted to intensify with increasing global temperature. This study represents the first investigation of gene expression in an Indo-Pacific coral species undergoing natural bleaching which involved the loss of algal symbionts. Quantitative real-time polymerase chain reaction experiments were conducted to select and evaluate coral internal control genes (ICGs), and to investigate selected coral genes of interest (GOIs) for changes in gene expression in nine colonies of the scleractinian coral Acropora millepora undergoing bleaching at Magnetic Island, Great Barrier Reef, Australia. Among the six ICGs tested, glyceraldehyde 3-phosphate dehydrogenase and the ribosomal protein genes S7 and L9 exhibited the most constant expression levels between samples from healthy-looking colonies and samples from the same colonies when severely bleached a year later. These ICGs were therefore utilised for normalisation of expression data for seven selected GOIs. Of the seven GOIs, homologues of catalase, C-type lectin and chromoprotein genes were significantly up-regulated as a result of bleaching by factors of 1.81, 1.46 and 1.61 (linear mixed models analysis of variance, P < 0.05), respectively. We present these genes as potential coral bleaching response genes. In contrast, three genes, including one putative ICG, showed highly variable levels of expression between coral colonies. Potential variation in microhabitat, gene function unrelated to the stress response and individualised stress responses may influence such differences between colonies and need to be better understood when designing and interpreting future studies of gene expression in natural coral populations. [ABSTRACT FROM AUTHOR]

A number of examples of independently duplicated regulatory genes have been identified in cnidarians, but the extent of this phenomenon and organization of these duplicated genes are unknown. Here we describe the identification of three pairs of independently duplicated homeobox genes in the anthozoan cnidarian, Acropora millepora. In each case, the pairs of paralogous genes are tightly linked, but the extent of sequence divergence implies that these do not reflect recent duplication events. The phenomenon is likely to be more general, as the examples reported here represent most of the limited number of Acropora homeobox genes for which genomic data are yet available. [ABSTRACT FROM AUTHOR]

Comparisons with cnidarians, long considered to be 'simple' animals, are providing crucial insights into the origins of conserved developmental mechanisms and the nature of the common metazoan ancestor. Traditionally, an extra germ layer and a second axis of body symmetry are the features that distinguish 'higher' Metazoa from lower animals such as cnidarians. Moreover, it was expected that 'lower' animals would have a simple gene set that corresponds to their simple morphology. Now, molecular genetic approaches are blurring the developmental divide between cnidarians and bilateral animals, and cnidarian sequencing projects are showing that the common metazoan ancestor was more genetically complex than was previously assumed. [ABSTRACT FROM AUTHOR]

Although corals are nominally diploblastic, the early development of Acropora millepora involves a process that clearly resembles gastrulation in higher metazoans. This similarity at the morphological level led us to search for the Acropora equivalents of genes whose key roles in gastrulation are conserved across the higher Metazoa. We here report the characterisation of one such gene, snail, which in both Drosophila and the mouse is expressed in cells undergoing an epithelial-mesenchyme transition and/or morphogenetic movements. In addition to an N-terminal SNAG domain, the Acropora snail protein contains four zinc fingers with sequences diagnostic for members of the snail protein subfamily. In situ hybridisation reveals expression in epithelial tissue in the central portion of one side of the flattened pre-gastrulation embryo, which continues to express snail as it is engulfed by its opposite layer. Comparison to snail expression during gastrulation in bilaterians such as Drosophila reveals striking similarities and suggests mechanistic, and possibly evolutionary, links between the processes of mesoderm formation in bilaterians and endoderm formation in the Cnidaria. [ABSTRACT FROM AUTHOR]

We have cloned a Hox-like gene, cnox-2Am, from a staghorn coral, Acropora millepora, an anthozoan cnidarian, and characterised its embryonic and larval expression. cnox-2Am and its orthologs in other cnidarians and Trichoplax most closely resemble the Gsx and, to a lesser extent, Hox 3/4 proteins. Developmental northern blots and in situ hybridisation are consistent in showing that cnox-2Am message appears in the planula larva shortly after the oral/aboral axis is formed following gastrulation. Expression is localised in scattered ectodermal cells with a restricted distribution along the oral/aboral body axis. They are most abundant along the sides of the cylindrical larva, rare in the oral region and absent from the aboral region. These cells, which on morphological grounds we believe to be neurons, are of two types; one tri-or multipolar near the basement membrane and a second extending projections in both directions from a mid-ectodermal nucleus. Anti-RFamide staining reveals neurons with a similar morphology to the cnox-2Am-expressing cells. However, RFamide-expressing neurons are more abundant, especially at the aboral end of the planula, where there is no cnox-2Am expression. The pattern of expression of cnox-2Am resembles that of Gsx orthologs in Drosophila and vertebrates in being expressed in a spatially restricted portion of the nervous system. [ABSTRACT FROM AUTHOR]

Presents findings related to the role of the lin-4 and let-7 RNA genes. Detection of let-7 RNA of ~21 nucleotides in samples from a wide variety of animal species, but not in RNA from several cnidarian and poriferan species; Lack of lin-4 RNA in the species that contained let-7; Expression of let-7 RNA in Caenorhabditis elegans and Drosophila; Conclusion that the let-7 regulatory RNA may control late temporal transitions during development across animal phylogeny.

Neurogenesis was examined in the central nervous system of embryos of the primitively wingless insect, the silverfish, Ctenolepisma longicaudata, using staining with toluidine blue (TB) and the incorporation of bromodeoxyuridine (BUdR). The silverfish has the same number and positioning of neuroblasts as seen in more advanced insects and the relative order in which the different neuroblasts segregate from the neuroectoderm is highly conserved between Ctenolepisma and the grasshopper, Schistocerca. Of the 31 different neuroblasts found in a thoracic segment, one (NB 6–3) has a much longer proliferative period in silverfish. Of the remainder, 14 have similar proliferative phases, while16 neuroblasts have extended their proliferative period by 10% of embryogenesis or greater in the grasshopper as compared with the silverfish. Both insects had similar periods of abdominal neurogenesis except that in the silverfish terminal ganglion a prominent set of neuroblasts continued dividing until close to hatching, possibly reflecting the importance of cercal sensory input in this insect. This comparison between silverfish and grasshopper shows that the shift from wingless to flying insects was not accompanied by the addition of any new neuronal lineages in the thorax. Instead, selected lineages underwent a proliferative expansion to supply the additional neurons presumably needed for flight. The expansion of specific thoracic lineages was accompanied by the reduction of the terminal abdominal lineages as flying insects began to de-emphasize their cercal sensory system. [ABSTRACT FROM AUTHOR]

Vertebrate Pax-6 and its Drosophila homolog eyeless play central roles in eye specification, although it is not clear if this represents the ancestral role of this gene class. As the most ”primitive” animals with true nervous systems, the Cnidaria may be informative in terms of the evolution of the Pax gene family. For this reason we surveyed the Pax gene complement of a representative of the basal cnidarian class (the Anthozoa), the coral Acropora millepora. cDNAs encoding two coral Pax proteins were isolated. Pax-Aam encoded a protein containing only a paired domain, whereas Pax-Cam also contained a homeodomain clearly related to those in the Pax-6 family. The paired domains in both proteins most resembled the vertebrate Pax-2/5/8 class, but shared several distinctive substitutions. As in most Pax-6 homologs and orthologs, an intron was present in the Pax-Cam locus at a position corresponding to residues 46/47 in the homeodomain. We propose a model for evolution of the Pax family, in which the ancestor of all of the vertebrate Pax genes most resembled Pax-6, and arose via fusion of a Pax-Aam-like gene (encoding only a paired domain) with an anteriorly-expressed homeobox gene resembling the paired -like class. [ABSTRACT FROM AUTHOR]

This study of the ultrastructure of the auditory sensilla of the New Zealand weta, Hemideina crassidens, is the first such study on a member of the orthopteran Superfamily Gryllacridoidea. Ultrastructure of the auditory sensilla is similar in all of the tibial mechanosensory organs, here called subgenual organ, intermediate organ and crista acoustica by analogy with comparable structures in Tettigoniidae. Distal to each sensory soma is a dendrite containing multiple ciliary rootlets that fuse into a single ciliary root. This splits into nine root processes that pass around the outside of the proximal basal body and then rejoin at the level of the distal basal body, distal to which the dendrite has a modified ciliary structure with a circlet of nine peripheral paired tubes and rods as it passes through the proximal extracellular space. It is then enclosed by a zone of scolopale cell cytoplasm before expanding into a dilatation within the distal extracellular space. In some sensilla this space is partially occluded by electron dense material which is part of the scolopale cell. Distal to the dilatation the cilium shrinks and ends surrounded by the scolopale cap. Accessory cells consist of glia enwrapping the sensory neuron in the region of its soma, the scolopale cell surrounding the ciliary portion of the dendrite, and the attachment cell surrounding the scolopale cell and scolopale cap and connected to them by desmosomes. The attachment cells are filled with microtubules in differing densities and orientations. Lamellae are present in the acellular matrix surrounding the attachment cells. Banded fibres, presumably of collagen, are also present in the matrix. [ABSTRACT FROM AUTHOR]

The microanatomy of the adult auditory system of the cricket, Teleogryllus commodus, is described with special attention to the number and arrangement of the groups of scolopidia forming the tympanal organ. In the proximal part of the prothoracic tibia, there is a large posterior tympanum and a smaller anterior tympanum, which are associated internally with two expanded chambers of the tracheal system. The tympanal organ, which is identical in both sexes, is situated on the dorsal surface of the anterior tympanal trachea. It contains about 70 scolopidia, divided into two main groups: the proximal group, whose attachment cells insert on large accessory cells dorsally within the tympanal organ, and the distal group, whose attachment cells insert on modified dorsal hypodermal cells. These groups can be further divided into five main types, each containing a relatively constant number of scolopidia: 1. proximal group A; 2. proximal main group with proximal neurons; 3. proximal main group with distal neurons; 4. proximal part of distal group; 5. distal part of distal group. These types differ consistently in the following features: location of sensory neuron, orientation of dendrite and scolopale cell, structure of scolopale cell, shape and orientation of attachment cell and its connection to the secondary attachment cell. [ABSTRACT FROM AUTHOR]

The anatomical development of the tympanal organ, the tracheal system and the tympana of Teleogryllus commodus is described. The tympanal organ is undifferentiated until instar 3 when the first scolopales appear. The organ develops in a proximo-distal direction but the more distal groups begin to form before the proximal groups are complete. All groups of scolopidia are represented in instar 7 but numbers of scolopidia continue to increase until the adult stage. Scolopales and scolopale cells are first formed at less than adult size and increase in size during subsequent instars. The subgenual organ is present in instar 1 and is complete in instar 4. The posterior and anterior tympanal trachease develop respectively from the tracheal trunk and tracheal branch, which are present from instar 2. These remain as simple, unconnected tubes until instar 7 and begin to show the adult form during instars 8 and 9, finally enlarging in conjunction with the tympana at the last two moults. The tympana first appear as hairless areas of cuticle in the larval stages: the posterior tympanum in instar 8 and anterior tympanum in instar 10, but the translucent appearance of the adult tympana is not present before the final moult. [ABSTRACT FROM AUTHOR]

The tracheal organ of the mesothoracic tibia of Teleogryllus is located in a corresponding position to the tympanal organ of the prothoracic tibia. The mesothoracic organ contains an average of only 12 scolopidia, the location of which corresponds to that of the proximal group A and proximal main group in the prothoracid tympanal organ. There are no scolopidia corresponding to the distal group of the tympanal organ. The variability in number of scolopidia is much greater in the mesothoracic organ than in the prothoracic organ. The adult tracheal system of the mesothoracic leg resembles the early nymphal tracheal system in both pro- and meso-thoracic legs. The development of the tracheal organ is usually complete by the sixth instar. The mesothoracic tracheal organ of the adult is broadly equivalent to the prothoracic tympanal organ of a fifth instar animal. [ABSTRACT FROM AUTHOR]