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E H Davidson

Publications and source records attributed to E H Davidson.

At least 145 records · Page 8Linked to original sources
PubMed1986

Insertion and/or deletion of many repeated DNA sequences in human and higher ape evolution.

The total numbers of copies of two repeat families, L1 (Kpn I) and Alu, have been measured in the DNA of four higher apes by an accurate titration method. The number of members of the Alu family repeats in the four genomes are as follows: human, 910,000; chimpanzee, 330,000; gorilla, 410,000; orangutan, 580,000. For the Kpn I family (3'-ward higher frequency region) the number of copies in these genomes are as follows: human, 107,000; chimpanzee, 51,000; gorilla, 64,000; orangutan, 84,000. Thermal stability measurements show that, although the families of repeats are moderately divergent in sequence, little net sequence change has occurred during the evolution of the higher apes. Most or all of the members of these families of repeats are interspersed throughout the genome. Therefore, a large number of events of insertion and/or deletion of these DNA sequences has occurred during higher primate evolution.

Animals↗
PubMed1986

Sequence of mRNA coding for bindin, a species-specific sea urchin sperm protein required for fertilization.

Bindin, a major protein of the sea urchin acrosome granule, mediates the species-specific adhesion and binding of sperm to egg required to effect fertilization. We report the isolation and sequence of bindin cDNA clones prepared from Strongylocentrotus purpuratus testis RNA. The bindin gene appears to be productively expressed only in males and only in testes. The protein is produced from a 51-kDa precursor, which is subsequently processed to yield the mature 24-kDa bindin protein.

Amino Acid Sequence↗
PubMed1985

Evolutionary conservation of DNA sequences expressed in sea urchin eggs and early embryos.

DNA sequence divergence measurements indicate that Strongylocentrotus franciscanus is more distinct from S. purpuratus and S. drobachiensis than these two species are from each other, in agreement with paleontological and morphological evidence. The evolutionary divergence of several classes of expressed DNA sequences was compared with that of total single-copy DNA. Between S. franciscanus and S. purpuratus the divergence of cDNA made from gastrula cytoplasmic poly(A)+ RNA is about half that of total single-copy DNA. Similar results were obtained for cDNA made from unfertilized egg poly(A)+ RNA. In contrast, sequences expressed in gastrula nuclear RNA have diverged almost as much as total single-copy DNA.

Animals↗
PubMed1985

Introduction of cloned DNA into sea urchin egg cytoplasm: replication and persistence during embryogenesis.

Cloned DNA sequences were introduced into the cytoplasm of unfertilized sea urchin eggs by a simple microinjection technique. Sperm was then added, and development allowed to proceed. If linearized plasmids are injected they form random concatenates, and during the early development of the embryos replicate repeatedly. Eukaryotic sequences are not required for replication of the exogenous DNA. Injected supercoiled DNAs neither ligate nor replicate. Both forms of exogenous DNA persist in the embryo through pluteus stage.

Animals↗
PubMed1985

Persistence and integration of cloned DNA in postembryonic sea urchins.

Cloned DNA was injected into the cytoplasm of unfertilized sea urchin eggs which were then fertilized and cultured in the laboratory through metamorphosis. The exogenous DNA replicated manyfold and persisted for weeks in a majority of growing larvae, as shown by hydridizing "dot blots" of the DNA of single individuals with appropriate labeled probes. After metamorphosis 5-15% of the juvenile sea urchins retained the exogenous sequences. Genomic integration of the exogenous sequence was observed in the DNA of a postmetamorphosis juvenile.

Animals↗
PubMed1984

Molecular indices of cell lineage specification in sea urchin embryos.

The origins of several of the differentiated cell lineages of the advanced sea urchin embryo are well defined. Cytological application of molecular probes to three lineages, those responsible for the formation of the skeleton, the gut, and the aboral ectodermal wall of the late embryo, has demonstrated expression of lineage-specific genes long before overt morphological differentiation. These observations lead to useful generalizations regarding the processes of gene regulation that underlie the molecular biology of cell lineage specification in the embryo.

Actins↗
PubMed1984

Regulation of cytoplasmic mRNA prevalence in sea urchin embryos. Rates of appearance and turnover for specific sequences.

Complementary DNA clones representing cytoplasmic poly(A) RNAs of sea urchin embryos were hybridized with metabolically labeled cytoplasmic RNA preparations and the rates of appearance and of decay for each transcript species were determined at the blastula-gastrula stage of development. The prevalence of the transcripts chosen for this study ranged, on average, from about one molecule per cell to a few hundred molecules per cell. The embryos were labeled continuously for 18 hours with [3H]guanosine, beginning at 24 hours post-fertilization. The amount of cytoplasmic [3H]poly(A) RNA that hybridized to each cloned sequence was determined and the specific activity of the [3H]GTP pool was measured in the same embryos. Rate constants for the entry of each transcript species into the cytoplasm, and for its decay were extracted from these data. The embryo transcript species identified by the cloned probes displayed a range of stabilities. Half-lives of only a few hours were measured both for a very rare sequence and for a moderately prevalent sequence. Other newly synthesized transcripts, including sequences that first appear during embryonic development, as well as sequences also represented in maternal RNA, are far more stable. We conclude that cytoplasmic RNA turnover rate is a major variable in the determination of the cytoplasmic level of expression of embryo genes. The entry rates of the transcripts into the cytoplasm also varied, from a few molecules per embryo per minute to several hundred, depending on the sequence. By comparing the mass of transcripts of a given sequence in the embryo to the mass of transcripts of that sequence accumulating as a result of new synthesis, the point at which embryo transcription accounts for the major fraction of the cytoplasmic molecules could be estimated. This calculation showed that for some sequences maternal transcripts persist well beyond gastrulation, while other embryo poly(A) RNA species are largely the product of transcription in the embryo nuclei from the blastula stage onwards. There is no single stage at which all maternal transcripts are suddenly replaced by newly synthesized embryo transcripts. Primary transcription rates were measured for two sequences by determining accumulation of label in these RNA species soon after addition of [3H]guanosine to the cultures. Comparing these rates to the cytoplasmic entry rates, we did not detect a significantly greater nuclear transcription of the sequence homologous to the cloned probe.

Animals↗
PubMed1984

Interspersed poly(A) RNAs of amphibian oocytes are not translatable.

The poly(A) RNA of the Xenopus oocytes has been shown to include both single copy and interspersed transcripts. Interspersed maternal poly(A) RNAs contain repetitive sequence elements distributed within regions transcribed from single copy sequences. When renatured these RNAs form partially double-stranded RNA networks, and as shown earlier this can be utilized for preparative separation of interspersed maternal transcripts from maternal transcripts that remain single-stranded after renaturation (Anderson et al., 1982). The translational activity of these RNA fractions was tested in vitro, in wheat germ and reticulocyte systems. While the single-stranded fractions supported protein synthesis, the interspersed oocyte RNAs displayed little translational activity. Translational activity was measured in vivo by injection into the Xenopus oocyte. Oocytes previously injected with globin mRNA were injected with increasing amounts of single-stranded, double-stranded, or denatured double-stranded RNA fractions, and the amount of globin synthesis was determined. It was found that single-stranded RNA competes with globin mRNA for the limited translational apparatus of the oocyte, as manifested by a quantitative reduction of globin synthesis. However, globin synthesis was not affected when double-stranded RNA, either in renatured or denatured form, was injected. We conclude that the interspersed RNAs are not translated within the oocyte. The amount of single and double-stranded RNAs loaded onto polysomes in the injected oocytes was also determined. Sixty seven per cent of radio-iodinated single-stranded RNA pelleted with polysomes in injected oocytes, whereas less than 20% of similarly labeled double-stranded RNA pelleted with polysomes. This value is similar to that obtained when partially hydrolyzed RNA is injected, suggesting again that essentially none of the interspersed RNA is translated in vivo. The significance of these findings in relation to translational regulation during oogenesis and early development is discussed.

Animals↗
PubMed1984

Sea urchin actin gene subtypes. Gene number, linkage and evolution.

The actin gene family of the sea urchin Strongylocentrotus purpuratus was analyzed by the genome blot method, using subcloned probes specific to the 3' terminal non-translated actin gene sequence, intervening sequence and coding region probes. We define an actin gene subtype as that gene or set of genes displaying homology with a given 3' terminal sequence probe, when hybridized at 55 degrees C, 0.75 M-Na+. By determining the often polymorphic restriction fragment band pattern displayed in genome blots by each probe, all, or almost all of the actin genes in this species could be classified. Our evidence shows that the S. purpuratus genome probably contains seven to eight actin genes, and these can be assigned to four subtypes. Studies of the expression of the genes (Shott et al., 1983) show that the actin genes of three of these subtypes code for cytoskeletal actins (Cy), while the fourth gives rise to a muscle-specific actin (M). We denote the array of S. purpuratus actin genes indicated by our data as follows. There is a single CyI actin gene, two or possibly three CyII genes (CyIIa, CyIIb, and possibly CyIIc), three CyIII actin genes (CyIIIa, CyIIIb, CyIIIc), and a single M actin gene. Comparative studies were carried out on the actin gene families of five other sea urchin species. At least the CyIIa and CyIIb genes are also linked in the Strongylocentrotus franciscanus genome, and this species also has a CyI gene, an M actin gene and at least two CyIII actin genes. It is not clear whether it also possesses a CyIIc actin gene, or a CyIIIc actin gene. The genome of a more closely related congener, Strongylocentrotus dröbachiensis, includes 3' terminal sequences suggesting the presence of a CyIIc gene. In S. franciscanus and S. dröbachiensis the first intron of the CyI gene has remained homologous with intron sequences of both the CyIIa and CyIIb genes, indicating a common origin of these three linked cytoskeletal actin genes. Of the four S. purpuratus 3' terminal subtype probe sequences only the CyI 3' terminal sequence has been conserved sufficiently during evolution to permit detection outside of the genus Strongylocentrotus. An unexpected observation was that a sequence found only in the 3' untranslated region of the CyII actin gene in the DNA of S. dröbachiensis and S. purpuratus is represented as a large family of interspersed repeat sequences in the genome of S. franciscanus.

Actins↗
PubMed1984

Insertion of a short repetitive sequence (D88I) in a sea urchin gene: a typical interspersed repeat?

A comparison has been made between the Sp88 gene regions of the DNAs of the sea urchins Strongylocentrotus purpuratus (Sp.) and Strongylocentrotus drobachiensis (Sd.). Examination of the 3' terminal part of the transcribed region revealed a short repetitive sequence present in Sd. but absent from Sp. A 12-nucleotide sequence present once in Sp. is almost perfectly duplicated at both ends of the repeat in Sd., suggesting that a mobile repeat was inserted in the Sd. genome. Other members of this family of repeated sequences occur in many interspersed locations in the genomes of both species. Except for the insertion duplication, the inserted sequence lacks direct or reverse repeats.

Animals↗
PubMed1984

Differential expression of the actin gene family of Strongylocentrotus purpuratus.

Molecular probes that individually recognize the 3' nontranslated regions of six actin genes were utilized in RNA gel blot hybridizations to detect RNAs complementary to each gene in embryonic and adult tissues of Strongylocentrotus purpuratus. In addition the probes were used in DNA excess filter hybridizations to estimate the relative contribution of the different actin genes. All six genes produce relatively stable mRNAs, and each displays a characteristic and distinct pattern of expression. On the basis of their expression in the egg, early embryos, or in adult coelomocytes, it is concluded that genes termed CyI, CyIIa, CyIIb, CyIIIa, and CyIIIb encode cytoskeletal actin proteins. Actin gene M gives rise to mRNAs that are found only in tissues containing muscle. Actin genes CyI, CyIIa, CyIIb, and M are expressed in both adult and embryonic tissues, giving rise to transcripts 2.1-2.2 kb in length. Expression of genes CyIIIa and CyIIIb is confined to the embryo. Gene CyIIIa provides the major embryonic actin mRNA, which is 1.8 kb in length. Three of the cytoskeletal actin genes are linked over a 30-kb distance in the S. purpuratus genome. We show that the actin genes included in this linkage group are not coordinately expressed.

Actins↗
PubMed1984

Proteins of the sea urchin egg vitelline layer.

The vitelline layers (VL) of unfertilized sea urchin eggs were isolated, and the diversity of their polypeptide constitutents estimated by two-dimensional polyacrylamide gel electrophoresis. At least 25 components are reproducibly observed. While VL polypeptides are almost certainly synthesized in the growing oocyte, they are not among the more prevalent newly synthesized proteins detected in oocytes that were isolated and labeled in vitro for 4 hr. A set of monoclonal antibodies was raised against VL components and partially characterized. The 31 monoclonals analyzed fell into 11 classes with respect to their avidity for VL proteins solubilized under mild and under strongly denaturing conditions, and to their reactions with surface components of the VLs of living eggs. Fluorescence microscopy showed diverse patterns of surface reactivity when different monoclonal antibodies were compared. Two of the monoclonal antibodies reacted with specific sets of three proteins each on VL protein blots. It is concluded that the VL is a complex structure containing a large number of different polypeptide components, the genes for several of which should now be experimentally accessible.

Animals↗
PubMed1984

Inducible expression of a cloned heat shock fusion gene in sea urchin embryos.

A fusion gene construct, in which the coding sequence for bacterial chloramphenicol acetyltransferase (CAT; acetyl-CoA: chloramphenicol 3-O-acetyltransferase, EC 2.3.1.28) was placed under the control of the regulatory region of the Drosophila gene encoding the 70-kilodalton heat shock protein [Di Nocera, P.P. & Dawid, I.B. (1983) Proc. Natl. Acad. Sci. USA 80, 7095-7098], was microinjected into the cytoplasm of unfertilized sea urchin eggs. Pluteus-stage embryos developing from the injected eggs were exposed to high temperature conditions that we found would elicit an endogenous sea urchin heat shock response. These embryos express the gene for CAT and, after heat treatment, display 8-10 times more CAT enzyme activity than do extracts from control embryos cultured at normal temperatures. The injected DNA is present in high molecular weight concatenates and, during development, is amplified about 100-fold. Amplified sequences are responsible for all or most of the induced CAT enzyme activity.

Acetyltransferases↗
PubMed1983

Interspersed sequence organization and developmental representation of cloned poly(A) RNAs from sea urchin eggs.

A random primed complementary DNA (cDNA) clone library constructed from total maternal poly(A) RNA of sea urchin eggs was screened with two cloned genomic repetitive sequence probes. Sets of cDNA clones reacting with each of these repetitive sequences were recovered. Most of the cloned transcripts included both single copy and repeat sequence elements. Except for the shared repeat sequence element, both the repetitive and single copy regions of the members of each set of clones failed to crossreact. Single copy probes linked to the repeats on the cloned maternal RNAs are represented in an asymmetric manner. It follows that many different genomic members of a given dispersed repeat sequence family are represented in the maternal RNA. RNA gel blots carried out with several repeat probes display about 10 to 20 prominent maternal poly(A) RNAs containing transcripts of each repetitive sequence family. The interspersed maternal transcripts are 3000 to 15,000 bases in length. Maternal transcripts reacting with single copy probes derived from the cloned cDNAs persist during embryonic development, and in some cases appear to be augmented by similar, newly synthesized embryo transcripts. Two examples were found in which additional transcripts of different length appear at specific developmental stages. The transcribed single copy regions are highly polymorphic in the genomes of different individual sea urchins, and comparisons of closely related sea urchin species showed that both the prevalence and length of specific maternal transcripts change rapidly during evolution. Nucleotide sequences of two homologous repeat elements occurring on different cloned transcripts displayed translation stop codons in every possible reading frame. These repeat sequences display structural features suggesting that there has been evolutionary transposition into transcription units active during oogenesis. The repeat elements and their flanking single copy regions reside either in very long 3' or 5'-terminal sequences, or in unprocessed intervening sequences in the maternal poly(A) RNA. These findings lead us to the proposal that the majority of the cytoplasmic poly(A) RNA in echinoderm eggs and early embryos is similar in form to RNAs that occur in the nucleus rather than to the messenger RNA of later cells.

Animals↗
PubMed1983

Mitochondrial DNA sequences in the nuclear genome of Strongylocentrotus purpuratus.

Two sea urchin embryo complementary DNA clones representing mitochondrial 16 S ribosomal RNA and cytochrome oxidase subunit I messenger RNA have been characterized. The cloned cDNAs are colinear with sea urchin mitochondrial DNA, and their identification is based on cross-hybridization with known restriction fragments of human mitochondrial DNA, and on nucleotide sequence determinations. The mitochondrial cDNA clones also displayed an unexpected reaction with specific genomic DNA sequences in gel blot hybridizations. Genomic phage lambda recombinants containing sequences hybridizing with the mitochondrial clones were isolated and the arrangement of these sequences was determined. The genomic region studied contains a sequence homologous with the 3' end of the mitochondrial 16 S rRNA gene, flanked on one side by what is possibly a complete copy of the cytochrome oxidase subunit I gene, and on the other by a duplication of a fragment of this gene. The nucleotide sequence divergence between the mitochondrial and nuclear homologues of the cytochrome oxidase subunit I gene varies for different regions of the gene, from about 13% to 25%, while there is about 8% sequence divergence between nuclear and mitochondrial versions of the 3' 16S rRNA sequence. The structure of the genomic mitochondrial sequence homologues indicates that during sea urchin evolution there occurred a germ-line transposition of a fragment of the mitochondrial genome into the nuclear DNA, followed by rearrangements and single nucleotide substitutions.

Animals↗
PubMed1983

Poly(A) RNA of the egg cytoplasm: structural resemblance to the nuclear RNA of somatic cells.

This paper concerns the structural characteristics of the poly(A) RNA stored in unfertilized amphibian and echinoderm eggs. Though located in the egg cytoplasm, at least two-thirds of these maternal transcripts display an interspersed sequence organization similar to that of nuclear RNA. In Xenopus laevis interspersed poly(A) RNA molecules are synthesized and deposited in the oocyte cytoplasm throughout the main growth phase of oogenesis. Regions of the sea urchin genome that are represented by interspersed maternal transcripts have been recovered from recombinant clone libraries. In one case the same single-copy sequence is found both in an abundant message-sized 1.6 kilobase (kb) maternal transcript and in a 7.5 kb maternal transcript that structurally resembles a precursor form and is not found in embryonic polysomes. In a second example considered, a 9.5 kb transcript was identified in embryo nuclear RNA that may be identical in structure with an interspersed maternal poly(A) RNA derived from the same transcription unit. Transcription of this sequence appears to be constitutive in somatic cell nuclei, though no homologous cytoplasmic RNAs are found after early cleavage. This may be a widespread form of regulation for transcription units expressed in female germ cells, and represented in the maternal poly(A) RNA pools of unfertilized eggs.

Animals↗