RNA synthesis in starfish embryos: developmental consequences of its inhibition by formycin

Selective inhibition of embryonic development in starfish by long-chain alkyl derivatives of UMP, TMP and AMP

Nucleoside analogs have been evaluated as useful tools for the investigation of the mechanism of cell differentiation. We thus examined the effects of nucleoside 5'-alkylphosphates (1-10) on the morphogenetic development of starfish embryos. These nucleotide derivatives were all permissive for their development up to the blastula stage, but the derivatives with lauryl side chain selectively inhibited one of the following stages into bipinnaria larvae. Among them, uridine 5'-laurylphosphate (2) inhibited gastrulation of the blastula, as is the case with the antibiotic tunicamycin, suggesting its inhibitory activity on sulfated and non-sulfated glycoprotein syntheses. Unexpectedly, adenosine 5'-laurylphosphate (8) was evaluated as a novel class of inhibitor that can arrest the embryos exactly at the late gastrula stage, absolutely inhibiting cell differentiation involved in the development of gastrointestinal tract. This is the first report on the appearance of biological activity due to the structural modification of a naturally-occurring molecule, which is critical to the morphogenetic development of multicellular organisms.

Molecular characterization of a novel nuclear transglutaminase that is expressed during starfish embryogenesis

We report the constitution and molecular characterization of a novel transglutaminase (EC 2.3.2.13) that starts to accumulate specifically in the nucleus in the starfish (Asterina pectinifera) embryo after progression through the early blastula stage. The cDNA for the nuclear transglutaminase was cloned and the cDNA-deduced sequence defines a single open reading frame encoding a protein with 737 amino acids and a predicted molecular mass of 83 kDa. A comparison of this transglutaminase with other members of the gene family revealed an overall sequence identity of 33-41%. A special sequence feature of this transglutaminase, which is not found in other transglutaminases, is the presence of nuclear localization signal-like sequences in the N-terminal region. Microinjection of hybrid constructs that encode the N-terminal segment fused to reporter proteins into the germinal vesicle of an oocyte produced chimeric proteins by transcription-coupled translation. It was found that the N-terminal segment alone was sufficient to effect nuclear accumulation of an otherwise cytoplasmic protein. These results suggest that the nuclear accumulation of the transglutaminase may play an important role in nuclear remodeling during early starfish embryogenesis.

Selective inhibition of gastrulation in the starfish embryo by albuside B, an inosine analogue

External application of 0.2-100 micrograms/ml albuside B inhibits gastrulation of the starfish (Asterina pectinifera) embryo. Treated embryos retain the late blastula morphology with the vegetal plate. However, the vegetal plate is unreactive to soybean agglutinin, a probe for observing the progenitor cells of the archenteron (mesendoderm) in a normal embryo. The effective period of the treatment is limited from 4 to 6 h after fertilization, a period immediately before the onset of blastulation. RNA synthesis is unaffected during the period of sensitivity. The selectivity of the inhibition shows that albuside B may be a useful tool for studying the mechanisms of mesendoderm differentiation.

Accumulation of multiacetylated forms of histones by trichostatin A and its developmental consequences in early starfish embryos

External application of 10 rig/ml (R)-trichostatin A (TSA), a potent and specific inhibitor of mammalian histone deacetylase, to the embryo of the starfish Asterina pectinifera inhibited development during the early gastrula stage before formation of mesenchyme cells. The TSA-sensitive period was limited to the mid-blastula stage before hatching. The pulse-chase experiment clearly demonstrated that TSA induced an accumulation of acetylated histone species in blastulae through inhibition of historic deacetylation. Similar blockage of development at the early gastrula stage was observed with n-butyrate, which has been known as a weak inhibitor of historic deacetylase. These results suggest an intimate role for historic acetylation-deacetylation equilibria in starfish development.