Synthesis of ribosomal RNA during sea-urchin development

Characterization of bep1 and bep4 antigens involved in cell interactions during Paracentrotus lividus development

We have identified and partially characterised two antigens, extracted with 3% butanol, from Paracentrotus lividus embryos dissociated at the blastula stage, and encoded by the cDNA clones previously described as bep1 and bep4 (bep-butanol extracted proteins). The cDNA fragments containing the specific central portions of bep1 and bep4 were expressed as MS2 polymerase fusion proteins in Escherichia coli. These two fusion proteins, called 1C1 (bep1) and 4A1 (bep4), were injected subcutaneously into rabbits and the corresponding polyclonal antibodies generated. Western blot analysis of proteins, extracted with 3% butanol, from sea urchin embryos at the blastula stage (b.e.p.), established that both antibodies recognize two 33 KDa proteins. Reducing and non-reducing electrophoretic conditions show that both antibodies against bep1 and bep4 related proteins react also with a protein band of a molecular weight 66 KDa, indicating that these two antigens probably exist as dimers. Immunolocalization with anti 1C1 and 4A1 antibodies shows the presence of the related antigens also on the cell surface. Fab fragments of the polyclonal antibodies against 1C1 and 4A1 inhibited reaggregation of sea urchin embryonic cells, dissociated from blastula stage embryos. This prevention of reaggregation indicates that these proteins probably play a role in cell interaction during sea urchin embryonic development.

Analysis of the sequence and expression during sea urchin development of two members of a multigenic family, coding for butanol-extractable proteins

Two cDNA clones related to Paracentrotus lividus butanol-extracted proteins, presumably belonging to cell surface proteins, were isolated by a lambda gt11 expression library of ovary poly A+ RNA. These clones, called bep1 and bep4, of 1,110 and 1,071 bp, respectively, belong to a multigene family. By sequencing analysis, a special structural organization in the coding region is detected. A single copy region is inserted between two regions different from each other but similar in the two clones, which constitute two perfectly preserved domains in the genome and are not always present together in the various members of this gene family. The bep1 and bep4 clones derive from two single genes that are polymorphic in the sea urchin genome. Expression of these clones was studied by Northern blot analysis. Both bep1 and bep4 are transcribed during oogenesis into mRNAs of 1.4 kb, which are stored in eggs and utilized during early embryogenesis. None of these RNAs is, in fact, detectable after the gastrula stage. Moreover, the transcripts of three other members of the family are present in eggs and at the 32 cell stage, but they are also synthesized in the early developmental stages.

Stress proteins by zinc ions in sea urchin embryos

In Paracentrotus lividus embryos, treatment with zinc ions induces the synthesis of the two major stress proteins with the same molecular weight as those induced by heat shock. The developmental stages responsive to zinc ion treatment are the same as those responsive to heat shock. However, zinc treatment induces a longer lasting synthesis of the stress proteins, and, unlike heat shock, does not induce thermotolerance and does not inhibit synthesis of the bulk proteins.

Isolation and characterization of a sea urchin hsp 70 gene segment

Three clones containing Paracentrotus lividus sea urchin DNA sequences which cross-hybridize to Drosophila heat shock protein (hsp) 70 gene were isolated. The sequence arrangements in the three cloned DNA inserts were compared by restriction and cross-hybridization analysis. The results showed that they contain four different genes related to one Drosophila hsp 70 gene. One of these genes was subcloned, and two of the isolated fragments were shown to hybridize to genomic DNA and to RNA from heat-treated sea urchin embryo.

Measurements of the specific activity of the nucleoside triphosphate pool of sea-urchin embryos following 8-3H-guanosine administration

The nucleoside triphosphate (NTP) pool during the early development of sea-urchin, Paracentrotus lividus, was measured using high-performance liquid chromatography (HPLC). Each NTP pool was measured at four stages between the eight-blastomere stage and the early blastula stage, as was the specific activity of each NTP following an initial administration of 8-3H-guanosine. Unexpectedly high UTP (uridine-5'-triphosphate) concentrations and radioactivity levels in UTP were observed. Studies of the sea-urchin, Strongilocentrotus purpuratus, also revealed elevated levels of 8-3H-guanosine incorporation into UTP. The present procedure was found to be suitable for the unequivocal identification of UTP.

Acquisition of thermotolerance in sea urchin embryos correlates with the synthesis and age of the heat shock proteins

Preheating at 31 degrees C induces thermotolerance in Paracentrotus lividus embryos, which therefore become able to withstand 1-h treatment at the otherwise lethal temperature of 35 degrees C, and to develop normally. The acquisition of thermotolerance is positively correlated with the amount of heat shock proteins produced during the 31 degrees C treatment. Evidence is provided that the heat shock proteins, although present in the embryo for long periods after synthesis, lose their effect on thermotolerance within 3 h of the cessation of synthesis.

Synthesis of heat shock proteins in dissociated sea urchin embryonic cells

Embryos dissociated into cells retain the stage-specific response to heat shock. The dissociated cells, irrespectively of whether they are reaggregated or not, undergo the developmental changes in their ability to respond to heat shock, at the same time as the entire embryos. The conclusion of the present experiments is that sea urchin embryonic cells become responsive to heat shock and produce heat shock proteins even in the absence of cell interactions.

Heat-shock proteins in sea urchin embryos. Transcriptional and posttranscriptional regulation

The production of heat-shock proteins in sea urchin embryos is accompanied by the appearance at the polysomal level of their relative mRNAs, as shown by their translation in a cell-free system; thus suggesting that the regulation of their production occurs at a transcriptional level. The mechanism for the inhibition of the bulk protein synthesis and for its reversal on the other hand should be looked for at a posttranscriptional level, since both these phenomena occur also in the presence of actinomycin D. The heat-shock proteins produced as early as at the mesenchyme blastula stage persist within the embryo at least till the pluteus stage.

Studies on the structure and possible function of the RNA "cap" in developing sea urchins

Paracentrotus lividus embryos at the hatching blastula stage very quickly incorporate radioactivity from labeled nucleosides (except uridine) or 32P- or methyl-labeled methionine into a portion of the RNA that has been identified as a "cap". The most probable sequence of this cap is m7G (5') ppp (5')mAmpCp. A very active "capping" and methylation of the "cap" of preexisting RNA molecules was shown to occur at the blastula stage.

Ribosomal RNA synthesis and the multiple, atypical nucleoli in cleaving embryos

The rate of ribosomal RNA synthesis per nucleus in cleaving sea urchin embryos is similar to the rate at later embryonic stages. The multiple, atypical nucleoli, present in early embryos and usually attributed to decreased ribosomal RNA synthesis, are beginning stages of nucleolar formation. Full nucleolar development requires more time than the brief interphase of the rapidly dividing cells.

Synthesis of RNA in isolated nuclei of sea urchin embryos

It is demonstrated that isolated nuclei of sea urchin embryos are able to incorporate radioactive nucleotides into RNA.Some properties of the incorporation system are described.