Conserved pattern of embryonic actin gene expression in several sea urchins and a sand dollar

The timing of expression of four actin genes and an RNA polymerase III-transcribed repeated sequence is correct in hybrid embryos of the sea urchin species Strongylocentrotus purpuratus and Lytechinus pictus

The accumulation of the mRNAs from four Strongylocentrotus purpuratus actin genes (the single muscle gene M, and three cytoskeletal genes CyI, CyIIIa, and CyIIIb) and of transcripts from an RNA polymerase III-transcribed repeated sequence family (SURF1) was followed throughout the early development of hybrid embryos of S. purpuratus and Lytechinus pictus. Each of the actin mRNAs appeared in hybrid embryos, constructed in either direction (Sp female X Lp male and Lp female X Sp male), at approximately the same time that they appear in normal S. purpuratus embryos. Transcripts of the repeated sequence family SURF1 also appeared at the correct time in the hybrid embryos, but were present at substantially reduced levels when contributed by the paternal genome (Lp female X Sp male). The accurate temporal expression of these genes indicates that both sets of hybrid embryos contain factors which regulate the timing of their transcription.

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.

Regulation of actin gene expression during sea urchin development

The progress that has been made in the last several years toward an understanding of the expression of the actin genes of the sea urchin is impressive. It serves as an excellent example of how the application of modern molecular biological techniques to a classic experimental system (the sea urchin embryo) can begin to give us insight into the processes of embryological development. There is reason to hope that general principles will emerge from studies such as these, but many questions are unanswered. With specific regard to the actin genes and proteins, there are some obvious questions. Are the actins encoded by the different genes functionally distinct, and what roles do they play in differentiation and development? How is the expression of each of these genes regulated; i.e., what molecules participate, how do they work, where are they located in the embryo, and when do they appear? The more general question is: How are these (and other) genes and proteins affected by, or how do they contribute to, determination and induction in early development? We hope that answers to the specific questions posed will provide important steps toward answers to the general question.

Quantitative assessment of actin transcript number in eggs, embryos, and tube feet of the sea star Pisaster ochraceus

Actin coding sequence cDNA probes were used to quantitate the number of transcripts in RNA from eggs, embryos, and tube feet of the sea star Pisaster ochraceus. Transcript concentrations were measured in both total RNA and in poly(A)+ RNA by titration and hybridization kinetic methods. Surprisingly, the actin transcript number in sea star eggs is two orders of magnitude greater than in sea urchin eggs. There are at least 2.9 X 10(5) actin transcripts per sea star egg, 1.2 X 10(5) per 48-h gastrula and 1.9 X 10(5) per 72-h gastrula. The number of actin transcripts per unit mass of extracted tube foot RNA is lower than in developmental stages. The relative abundance and size of actin transcripts was determined by Northern and dot blot analyses using probes containing actin coding DNA or 3'-untranslated-region sequences. The actin transcript in eggs and embryos is 2,300 nucleotides (nt) long and originates from the Cy (cytoplasmic) gene class. In tube feet, the most abundant actin transcript is 2,200 nt long and originates from the M (muscle) gene class. Tube feet also contain, at lower abundance, 2,300-nt transcripts of the Cy gene type expressed in eggs and embryos.

Quantitative assessment of actin transcript number in eggs, embryos, and tube feet of the sea star Pisaster ochraceus

Actin coding sequence cDNA probes were used to quantitate the number of transcripts in RNA from eggs, embryos, and tube feet of the sea star Pisaster ochraceus. Transcript concentrations were measured in both total RNA and in poly(A)+ RNA by titration and hybridization kinetic methods. Surprisingly, the actin transcript number in sea star eggs is two orders of magnitude greater than in sea urchin eggs. There are at least 2.9 X 10(5) actin transcripts per sea star egg, 1.2 X 10(5) per 48-h gastrula and 1.9 X 10(5) per 72-h gastrula. The number of actin transcripts per unit mass of extracted tube foot RNA is lower than in developmental stages. The relative abundance and size of actin transcripts was determined by Northern and dot blot analyses using probes containing actin coding DNA or 3'-untranslated-region sequences. The actin transcript in eggs and embryos is 2,300 nucleotides (nt) long and originates from the Cy (cytoplasmic) gene class. In tube feet, the most abundant actin transcript is 2,200 nt long and originates from the M (muscle) gene class. Tube feet also contain, at lower abundance, 2,300-nt transcripts of the Cy gene type expressed in eggs and embryos.

Specific stimulation of actin gene transcription by epidermal growth factor and cycloheximide

Stimulation of quiescent AKR-2B mouse embryo cells with epidermal growth factor (EGF) results in a rapid and specific induction of actin mRNA sequences. These mRNAs include those coding for both beta- and gamma-cytoskeletal, but not alpha-skeletal muscle, actin isotypes. Elongation of nascent RNA chains in isolated nuclei (run-off transcription) demonstrates that the mRNA accumulation is preceded by an increase in actin gene transcription. This increase is transient, however, and is followed by a rapid attenuation of transcriptional activity. An inhibitor of protein synthesis, cycloheximide, was also found to induce beta- and gamma-actin mRNA accumulation. Furthermore, the simultaneous addition of EGF and cycloheximide produced a synergistic effect on actin sequences in both steady-state nuclear and polysomal RNA. Run-off transcription experiments demonstrate that this synergistic effect results from an increase in the magnitude and duration of actin gene transcription. It is also specific in that alpha-tubulin gene transcription is not similarly affected. These data suggest the existence of a specific labile repressor of actin gene transcription.

Three sea urchin actin genes show different patterns of expression: muscle specific, embryo specific, and constitutive

The expression of three different actin genes in the sea urchin, Strongylocentrotus purpuratus, was monitored in embryos and adult tissues by using untranslated mRNA sequences as specific hybridization probes. Three distinct patterns of expression were found: muscle specific, embryo specific, and constitutive (i.e., present in all tissues examined). The actin genes encoding the muscle-specific and constitutively expressed genes were each found to be present once in the haploid genome. The embryo-specific probe could derive from either a single gene or a small subset of actin genes. These data demonstrate that at least three members of the sea urchin actin gene family are expressed in distinct ways and thus are probably associated with different regulatory programs of gene expression necessary for development of this metazoan.

Three sea urchin actin genes show different patterns of expression: muscle specific, embryo specific, and constitutive

The expression of three different actin genes in the sea urchin, Strongylocentrotus purpuratus, was monitored in embryos and adult tissues by using untranslated mRNA sequences as specific hybridization probes. Three distinct patterns of expression were found: muscle specific, embryo specific, and constitutive (i.e., present in all tissues examined). The actin genes encoding the muscle-specific and constitutively expressed genes were each found to be present once in the haploid genome. The embryo-specific probe could derive from either a single gene or a small subset of actin genes. These data demonstrate that at least three members of the sea urchin actin gene family are expressed in distinct ways and thus are probably associated with different regulatory programs of gene expression necessary for development of this metazoan.

Transcripts of paternal and maternal actin gene alleles are present in interspecific sea urchin embryo hybrids

Analysis of actin-coding RNAs in interspecific hybrid sea urchin embryos of Strongylocentrotus purpuratus and Lytechinus variegatus, and S. purpuratus and S. droebachienis has revealed the presence of transcripts from both paternal and maternal S. purpuratus actin gene alleles. In the L. variegatus female X S. purpuratus male embryos transcripts from at least two different paternal actin gene alleles are present in both the blastula and prism stages. In the reciprocal S. purpuratus female X L. variegatus male embryos, the same two maternal (S. purpuratus) alleles were also expressed as RNA in blastula. The S. droebachiensis female X S. purpuratus male embryos appear to contain transcripts from at least one paternal actin gene allele at the blastula stage. The paternally derived actin-coding RNAs are the same size as the mature actin mRNAs expressed in normal S. purpuratus embryos. Since all known S. purpuratus actin genes contain at least two introns, the paternal alleles are not only transcribed in the hybrid embryos, but also the primary transcripts are probably processed to mature mRNA. An explanation of the diversity of observations in the literature on paternal genome expression in hybrid sea urchin embryos is discussed.

Changes in the quantity of histone and actin messenger RNA during the development of preimplantation mouse embryos

Actin and histone H3 mRNA levels in mouse eggs and early embryos have been measured by use of recombinant DNA probes having sequence homology to those mRNA species. Total nucleic acid was extracted from pools of unfertilized eggs, two-cell embryos, eight-cell embryos, and blastocysts. The nucleic acids were resolved electrophoretically, bound to diazotized paper following Northern transfer, and hybridized with 32P-labeled histone or actin DNA probes. Our findings demonstrate that there is a maternal store of histone and actin mRNA in the unfertilized egg but that this mRNA pool is reduced roughly 10-fold on an embryo basis by the mid-two-cell stage. Following this reduction of maternal mRNA, histone and actin mRNA accumulation from the eight-cell cleavage stage to the blastocyst increases proportionally to cell number and appears to be controlled by zygote genome transcription.