We report the first complete genome sequence of a marine invertebrate virus. White spot bacilliform virus (WSBV; or white spot syndrome virus) is a major shrimp pathogen with a high mortality rate and a wide host range. Its double-stranded circular DNA genome of 305,107 bp contains 181 open reading frames (ORFs). Nine homologous regions containing 47 repeated minifragments that include direct repeats, atypical inverted repeat sequences, and imperfect palindromes were identified. This is the largest animal virus that has been completely sequenced. Although WSBV is morphologically similar to insect baculovirus, the two viruses are not detectably related at the amino acid level. Rather, some WSBV genes are more homologous to eukaryotic genes than viral genes. In fact, sequence analysis indicates that WSBV differs from all known viruses, although a few genes display a weak homology to herpesvirus genes. Most of the ORFs encode proteins that bear no homology to any known proteins, either suggesting that WSBV represents a novel class of viruses or perhaps implying a significant evolutionary distance between marine and terrestrial viruses. The most unique feature of WSBV is the presence of an intact collagen gene, a gene encoding an extracellular matrix protein of animal cells that has never been found in any viruses. Determination of the genome of WSBV will facilitate a better understanding of the molecular mechanism underlying the pathogenesis of the WSBV virus and will also provide useful information concerning the evolution and divergence of marine and terrestrial animal viruses at the molecular level.White spot bacilliform virus (WSBV) or white spot syndrome virus (WSSV) is a major shrimp pathogen that is highly virulent in penaeid shrimp, the most important species used in aquaculture, and can also infect most species of crustacean (15, 32). Infection of penaeid shrimp by WSBV can result in mortality of up to 90 to 100% within 3 to 7 days (57). A major outbreak of WSBV infection in 1993 resulted in a 70% reduction in shrimp production in China (14, 57) and has raised major concerns in aquaculture around the world. Prevention and inhibition of infection by this virus can be difficult due largely to the ability of WSBV to survive for a long time in the environment (2 years in a shrimp pond) and also due to a poor understanding of this virus at the molecular level.WSBV was originally classified as an unassigned member of the Baculoviridae because of its rod-shaped, enveloped morphology (20). However, it was recently excluded from the baculovirus family and is temporarily unclassified due to the lack of molecular information (53). The virus is known generally as white spot syndrome virus (WSSV) (31), and a new genus name, Whispovirus, was proposed by Vlak et al. (48). Sequence analysis of individual genes and proteins later showed that most WSBV proteins bear poor sequence homology to baculovirus proteins but have repeated regions similar to those of some baculoviruses. To understand the molecular basis of viral repl...

Cardiac development arises from two sources of mesoderm progenitors, the first heart field (FHF) and the second (SHF). Mesp1 has been proposed to mark the most primitive multipotent cardiac progenitors common for both heart fields. Here, using clonal analysis of the earliest prospective cardiovascular progenitors in a temporally controlled manner during early gastrulation, we found that Mesp1 progenitors consist of two temporally distinct pools of progenitors restricted to either the FHF or the SHF. FHF progenitors were unipotent, whereas SHF progenitors were either unipotent or bipotent. Microarray and single-cell PCR with reverse transcription analysis of Mesp1 progenitors revealed the existence of molecularly distinct populations of Mesp1 progenitors, consistent with their lineage and regional contribution. Together, these results provide evidence that heart development arises from distinct populations of unipotent and bipotent cardiac progenitors that independently express Mesp1 at different time points during their specification, revealing that the regional segregation and lineage restriction of cardiac progenitors occur very early during gastrulation.

Mouse heart development arises from -expressing cardiovascular progenitors (CPs) that are specified during gastrulation. The molecular processes that control early regional and lineage segregation of CPs have been unclear. We performed single-cell RNA sequencing of wild-type and-null CPs in mice. We showed that populations of CPs are molecularly distinct and span the continuum between epiblast and later mesodermal cells, including hematopoietic progenitors. Single-cell transcriptome analysis of-deficient CPs showed that Mesp1 is required for the exit from the pluripotent state and the induction of the cardiovascular gene expression program. We identified distinct populations of CPs that correspond to progenitors committed to different cell lineages and regions of the heart, identifying the molecular features associated with early lineage restriction and regional segregation of the heart at the early stage of mouse gastrulation.

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Background: Transglutaminases (TGases) form a group of enzymes that have many different substrates and among the most well known are fibrin for Factor XIIIa and the clotting protein in crustaceans. We also found that TGase is an abundant protein in the hematopoietic tissue (Hpt) cells of crayfish and hence we have studied the possible function of this enzyme in hematopoiesis.