Developmental dynamics of myogenesis in the shipworm <Emphasis Type="Italic">Lyrodus pedicellatus</Emphasis> (Mollusca: Bivalvia)

Background

The shipworm Lyrodus pedicellatus is a wood-boring bivalve with an unusual vermiform body. Although its larvae are brooded, they retain the general appearance of a typical bivalve veliger-type larva. Here, we describe myogenesis of L. pedicellatus revealed by filamentous actin labelling and discuss the data in a comparative framework in order to test for homologous structures that might be part of the bivalve (larval) muscular ground pattern.

Results

Five major muscle systems were identified: a velum retractor, foot retractor, larval retractor, a distinct mantle musculature and an adductor system. For a short period of larval life, an additional ventral larval retractor is present. Early in development, a velum muscle ring and an oral velum musculature emerge. In late stages the lateral and dorsal mantle musculature, paired finger-shaped muscles, an accessory adductor and a pedal plexus are formed. Similar to other bivalve larvae, L. pedicellatus exhibits three velum retractor muscles, but in contrast to other species, one of them disappears in early stages of L. pedicellatus. The remaining two velum retractors are considerably remodelled during late larval development and are most likely incorporated into the elaborate mantle musculature of the adult.

Conclusions

To our knowledge, this is the first account of any larval retractor system that might contribute to the adult bodyplan of a (conchiferan) mollusk. A comparative analysis shows that a pedal plexus, adductors, a larval velum ring, velum retractors and a ventral larval retractor are commonly found among bivalve larvae, and thus most likely belong to the ground pattern of the bivalve larval musculature.

     

The broadcast spawning Caribbean shipworm,Teredothyra dominicensis (Bivalvia,Teredinidae), has invaded and become established in the eastern Mediterranean Sea

Teredinids, commonly referred to as shipworms, are wood-boring bivalves estimated to cause over one billion dollars’ worth of damage to submerged wooden structures per annum. This paper reports the detection and establishment of the Caribbean shipworm Teredothyra dominicensis (Bivalvia, Teredinidae) in the eastern Mediterranean Sea. Identification was confirmed using an integrative taxonomical approach combining morphology, morphometry and molecular markers (COI-5P and 18S), thus improving both the taxonomic resolution and tractability of this invasive species. Sequence comparisons between indigenous Caribbean and Mediterranean specimens were at least 99 % identical. Wooden panels placed at the site of discovery were infested exclusively by T. dominicensis with specimens of varying size and age, indicating multiple settlement events and the presence of breeding populations in the region. Anatomical and behavioural observations confirm the species as a broadcast spawner with larvae undergoing planktotrophic development, thus distribution range is potentially extensive. Of the possible introduction vectors, transport via ballast water is proposed as the most likely. The establishment of breeding populations of a tropical teredinid in the Mediterranean is of considerable concern as tropical species are particularly destructive and degrade wood more rapidly than the species currently found in the region. This threat is likely to increase in severity due to global warming, as increases in temperature and salinity may lead to an increase in the distribution range, development rate and boring activity of teredinids.     

Identification of an S-locus glycoprotein allele introgressed from B. napus ssp. rapifera to B. napus ssp. oleifera.

We have previously described a developmentally regulated mRNA in maize that accumulates in mature embryos and is involved in a variety of stress responses in the plant. The sequence of the encoded 16 kDa protein (MA16) predicts that it is an RNA-binding protein, since it possesses a ribonucleoprotein consensus sequence-type RNA-binding domain (CS-RBD). To assess the predicted RNA binding property of the protein and as a starting point to characterize its function we have used ribohomopolymer-binding assays. Here we show that the MA16-encoded protein binds preferentially to uridine- and guanosine-rich RNAs. In light of these results a likely role for this protein in RNA metabolism during late embryogenesis and in the stress response is discussed.     

Molecular evolution of mitochondrial 12S RNA and cytochrome b sequences in the pantherine lineage of Felidae

DNA sequence comparisons of two mitochondrial DNA genes were used to infer phylogenetic relationships among 17 Felidae species, notably 15 in the previously described pantherine lineage. The polymerase chain reaction (PCR) was used to generate sequences of 358 base pairs of the mitochondrial 12S RNA gene and 289 base pairs of the cytochrome b protein coding gene. DNA sequences were compared within and between 17 felid and five nonfelid carnivore species. Evolutionary trees were constructed using phenetic, cladistic, and maximum likelihood algorithms. The combined results suggested several phylogenetic relationships including (1) the recognition of a recently evolved monophyletic genus Panthera consisting of Panthera leo, P. pardus, P. onca, P. uncia, P. tigris, and Neofelis nebulosa; (2) the recent common ancestry of Acinonyx jubatus, the African cheetah, and Puma concolor, the American puma; and (3) two golden cat species, Profelis temmincki and Profelis aurata, are not sister species, and the latter is strongly associated with Caracal caracal. These data add to the growing database of vertebrate mtDNA sequences and, given the relatively recent divergence among the felids represented here (1-10 Myr), allow 12S and cytochrome b sequence evolution to be addressed over a time scale different from those addressed in most work on vertebrate mtDNA.      

Mosses,Liverworts, and Hornworts Screened for Antitumor Agents

The National Cancer Institute’s record of bryophytes (mosses, liverworts, and hornworts) screened for biologically active chemicals is reviewed. In 1977, an extract of a moss from Maryland, Polytrichum ohioense, showed cytotoxicity in KB cell culture, but antitumor activity was not discovered in bryophytes until 1980. This led to a greater emphasis in collecting and screening bryophytes during 1980–1981. Samples weighing 0.5–2 kg (dried) were collected for each of 208 species and varieties. These included 184 species in 97 genera of mosses, 23 species in 16 genera of liverworts, and 1 hornwort. The methodologies for field work, extraction, and screening are briefly described. The screening results are summarized in a table listing all species alphabetically by family and by genus. For each species, the origin of the sample (country or state), collector’s number, extract number, type of extract, and 3 bioassays employed (including the dose levels used and toxic dose for the P388 lymphocytic leukemia assay) are indicated. Extracts of 75 species were toxic; extracts of 43 species were active. Activity was especially noted in the moss families Thuidiaceae, Mniaceae, Neckeraceae, Hypnaceae, Brachytheciaceae, Polytrichaceae, Dicranaceae, and Grimmiaceae. The authors suggest that bryophytes are a promising source for discovery of novel biologically active compounds. The possibility that biological activity in bryophytes may be the result of allelopathy, or the reputed ability of bryophytes to accumulate toxic substances, is considered.     

Role of stress-activated OCT4A in the cell fate decisions of embryonal carcinoma cells treated with etoposide

Tumor cellular senescence induced by genotoxic treatments has recently been found to be paradoxically linked to the induction of “stemness.” This observation is critical as it directly impinges upon the response of tumors to current chemo-radio-therapy treatment regimens. Previously, we showed that following etoposide (ETO) treatment embryonal carcinoma PA-1 cells undergo a p53-dependent upregulation of OCT4A and p21Cip1 (governing self-renewal and regulating cell cycle inhibition and senescence, respectively). Here we report further detail on the relationship between these and other critical cell-fate regulators. PA-1 cells treated with ETO display highly heterogeneous increases in OCT4A and p21Cip1 indicative of dis-adaptation catastrophe. Silencing OCT4A suppresses p21Cip1, changes cell cycle regulation and subsequently suppresses terminal senescence; p21Cip1-silencing did not affect OCT4A expression or cellular phenotype. SOX2 and NANOG expression did not change following ETO treatment suggesting a dissociation of OCT4A from its pluripotency function. Instead, ETO-induced OCT4A was concomitant with activation of AMPK, a key component of metabolic stress and autophagy regulation. p16ink4a, the inducer of terminal senescence, underwent autophagic sequestration in the cytoplasm of ETO-treated cells, allowing alternative cell fates. Accordingly, failure of autophagy was accompanied by an accumulation of p16ink4a, nuclear disintegration, and loss of cell recovery. Together, these findings imply that OCT4A induction following DNA damage in PA-1 cells, performs a cell stress, rather than self-renewal, function by moderating the expression of p21Cip1, which alongside AMPK helps to then regulate autophagy. Moreover, this data indicates that exhaustion of autophagy, through persistent DNA damage, is the cause of terminal cellular senescence.