Development of the rhopalial nervous system in Aurelia sp.1 (Cnidaria, Scyphozoa)

We examined the development of the nervous system in the rhopalium, a medusa-specific sensory structure, in Aurelia sp.1 (Cnidaria, Scyphozoa) using confocal microscopy. The rhopalial nervous system appears primarily ectodermal and contains neurons immunoreactive to antibodies against tyrosinated tubulin, taurine, GLWamide, and FMRFamide. The rhopalial nervous system develops in an ordered manner: the presumptive gravity-sensing organ, consisting of the lithocyst and the touch plate, differentiates first; the “marginal center,” which controls swimming activity, second; and finally, the ocelli, the presumptive photoreceptors. At least seven bilaterally arranged neuronal clusters consisting of sensory and ganglion cells and their neuronal processes became evident in the rhopalium during metamorphosis to the medusa stage. Our analysis provides an anatomical framework for future gene expression and experimental studies of development and functions of scyphozoan rhopalia

Diversity, Phylogeny and Expression Patterns of Pou and Six Homeodomain Transcription Factors in Hydrozoan Jellyfish Craspedacusta sowerbyi

Formation of all metazoan bodies is controlled by a group of selector genes including homeobox genes, highly conserved across the entire animal kingdom. The homeobox genes from Pou and Six classes are key members of the regulation cascades determining development of sensory organs, nervous system, gonads and muscles. Besides using common bilaterian models, more attention has recently been targeted at the identification and characterization of these genes within the basal metazoan phyla. Cnidaria as a diploblastic sister group to bilateria with simple and yet specialized organs are suitable models for studies on the sensory organ origin and the associated role of homeobox genes. In this work, Pou and Six homeobox genes, together with a broad range of other sensory-specific transcription factors, were identified in the transcriptome of hydrozoan jellyfish Craspedacusta sowerbyi. Phylogenetic analyses of Pou and Six proteins revealed cnidarian-specific sequence motifs and contributed to the classification of individual factors. The majority of the Craspedacusta sowerbyi Pou and Six homeobox genes are predominantly expressed in statocysts, manubrium and nerve ring, the tissues with sensory and nervous activities. The described diversity and expression patterns of Pou and Six factors in hydrozoan jellyfish highlight their evolutionarily conserved functions. This study extends the knowledge of the cnidarian genome complexity and shows that the transcriptome of hydrozoan jellyfish is generally rich in homeodomain transcription factors employed in the regulation of sensory and nervous functions

Is firm productivity related to firm size and age? the case of large Australian firms

We investigate the relationship between productivity, size and age of large Australian firms employing more than 100 employees or holding assets in excess of $100 million. In addition, we also investigate the extent of productivity persistence among these firms by looking at transition matrices of productivity distribution and productivity-rank mobility. The empirical study is based on the IBISWorld database used to estimate translog cost function to measure (a residual based) productivity. We find evidence, though somewhat weak, that larger and older firms are on average less productive. Furthermore, we find stronger evidence for a high degree of inertia in terms of productivity ranking within an industry