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W R Jeffery

Publications and source records attributed to W R Jeffery.

At least 37 records · Page 2Linked to original sources
PubMed1995

A maternal RNA localized in the yellow crescent is segregated to the larval muscle cells during ascidian development.

A cDNA library prepared from one-cell zygotes of the ascidian Styela clava was screened with probes from isolated cellular fractions to identify clones encoding RNAs localized in the yellow crescent or myoplasm, a cytoskeletal domain with multiple developmental roles. The differential screen yielded five overlapping cDNA (Styela clava yellow crescent or ScYC) clones encoding a 1.2-kb polyadenylated RNA (yellow crescent or YC RNA) which is present throughout embryonic development. In situ hybridization confirmed that YC RNA is localized in the yellow crescent. Antisense probes containing the 3' region of YC RNA hybridize with multiple maternal and zygotic RNAs, suggesting sequence homologies with other transcripts. YC RNA was first detected during oogenesis when transcripts accumulate in the perinuclear region of vitellogenic oocytes and are gradually translocated to the cortex. The YC transcripts are localized in the cortex of unfertilized eggs but after fertilization segregate with the myoplasm to the yellow crescent. During cleavage most YC transcripts enter the primary muscle cell lineage. YC RNA is also present in the secondary muscle cells. The YC transcripts are retained in the myoplasm of oocytes and eggs extracted with the non-ionic detergent Triton X-100, suggesting that they are associated with the cytoskeleton. The nucleotide sequence of the longest ScYC clone contains a short open reading frame (ORF). The YC ORF would encode a putative polypeptide of 49 amino acids, which shows no significant homology to known proteins. Several features of the YC RNA, however, suggest that it functions as an RNA rather than as a protein coding molecule. We conclude that the myoplasm contains a novel maternal RNA which is associated with the cytoskeleton and segregated to the muscle cells during ascidian embryogenesis. The YC RNA may be a new member of a growing family of noncoding RNAs that play important roles in growth and development.

Amino Acid Sequence↗
PubMed1995

Multiple origins of anural development in ascidians inferred from rDNA sequences.

Ascidians exhibit two different modes of development. A tadpole larva is formed during urodele development, whereas the larval phase is modified or absent during anural development. Anural development is restricted to a small number of species in one or possibly two ascidian families and is probably derived from ancestors with urodele development. Anural and urodele ascidians constitute a model system in which to study the evolution of development, but the phylogeny of anural development has not been resolved. Classification based on larval characters suggests that anural species are monophyletic, whereas classification according to adult morphology suggests they are polyphyletic. In the present study, we have inferred the origin of anural development using rDNA sequences. The central region of 18S rDNA and the hypervariable D2 loop of 28S rDNA were amplified from the genomic DNA of anural and urodele ascidian species by the polymerase chain reaction and sequenced. Phylogenetic trees inferred from 18S rDNA sequences of 21 species placed anural developers into two discrete groups corresponding to the Styelidae and Molgulidae, suggesting that anural development evolved independently in these families. Furthermore, the 18S rDNA trees inferred at least four independent origins of anural development in the family Molgulidae. Phylogenetic trees inferred from the D2 loop sequences of 13 molgulid species confirmed the 18S rDNA phylogeny. Anural development appears to have evolved rapidly because some anural species are placed as closely related sister groups to urodele species. The phylogeny inferred from rDNA sequences is consistent with molgulid systematics according to adult morphology and supports the polyphyletic origin of anural development in ascidians.

Amphibians↗
PubMed1995

Chasing tails in ascidians: developmental insights into the origin and evolution of chordates.

The ascidian tadpole larva is regarded as a prototype of the ancestral chordate. Here we consider recent studies on the development of the tadpole larva that provide new insights into chordate origins and evolution. The notochord of ascidian larvae and vertebrates appear to be homologous structures based on their induction by endoderm and expression of the Brachyury (T) gene. The muscle cells of ascidian larvae also appear homologous to those of vertebrates based on their expression of bHLH myogenic and muscle-type actin genes, although they are specified by cytoplasmic determinants localized in the egg as well as embryonic induction. Studies of the tailless larvae of anural ascidians have resulted in the identification of Manx, a gene that may control tail development and evolution. These and other results support the ascidian tadpole prototype for the ancestral chordate.

Actins↗
PubMed1994

Heterochronic expression of an adult muscle actin gene during ascidian larval development.

Adultation is a heterochronic mode of development in which adult tissues and organs differentiate precociously during the larval phase. We have investigated the expression of an adult muscle actin gene during adultation in the ascidian Molgula citrina. Ascidians contain multiple muscle actin genes which are expressed in the larva, the adult, or during both phases of the life cycle. In ascidian species with conventional larval development, the larval mesenchyme cells, which are believed to be progenitors of the adult mesoderm, remain undifferentiated and do not express the muscle actin genes. In M. citrina, the mesenchyme cells differentiate precociously during larval development, suggesting a role in adultation. An adult muscle actin gene from M. citrina was obtained by screening a mantle cDNA library with a probe containing the coding region of SpMA1, a Styela plicata adult muscle actin gene. The screen yielded a cDNA clone designated McMA1, which contained virtually the complete coding and 3' noncoding regions of a muscle actin gene. The deduced McMA1 and SpMA1 proteins exhibit 97% identity in amino acid sequence and may be encoded by homologous genes. The McMA1 gene is expressed in juveniles and adults, but not in larval tail muscle cells, suggesting that it is an adult muscle actin gene. In situ hybridization with a 3' non-coding region probe was used to determine whether the McMA1 gene is expressed during adultation in M. citrina. McMA1 mRNA was first detected exclusively in the mesenchyme cells during the late tailbud stage and continued to accumulate in these cells during their migration into the future body cavity and heart primordium in the hatched larva. The McMA1 transcripts persisted in mesenchyme cells after larval metamorphosis. It is concluded that an adult muscle actin gene shows a heterochronic shift of expression into the larval phase during adultation in M. citrina.

Actins↗
PubMed1993

Evolution of the chordate muscle actin gene.

The ascidians Styela plicata, S. clava, and Mogula citrina are urochordates. The larvae of urochordates are considered to morphologically resemble the ancestral vertebrate. We asked whether larval and adult ascidian muscle actin sequences are nonmusclelike as in lower invertebrates, musclelike as in vertebrates, or possess characteristics of both. Nonmuscle and muscle actin cDNA clones from S. plicata were sequenced. Based on 27 diagnostic amino acids, which distinguish vertebrate muscle actin from other actins, we found that the deduced protein sequences of ascidian muscle actins exhibit similarities to both invertebrate and vertebrate muscle actins. A comparison to muscle actins from different vertebrate and invertebrate phylogenetic groups suggested that the urochordate muscle actins represent a transition from a nonmusclelike sequence to a vertebrate musclelike sequence. The ascidian adult muscle actin is more similar to skeletal actin and the larval muscle actin is more similar to cardiac actin, which indicates that the divergence of the skeletal and cardiac isoforms occurred before the emergence of urochordates. The muscle actin gene may be a powerful probe for investigating the chordate lineage.

Actins↗
PubMed1993

An ankryin-like protein in ascidian eggs and its role in the evolution of direct development.

An erythrocyte anti-ankryin antibody was used to investigate the presence and distribution of ankryin in eggs and embryos of ascidian species with different modes of development. In eggs of the indirect developer Ascidia ceratodes, anti-ankryin reacted with a 210 kDa polypeptide which has an electrophoretic mobility similar to the vertebrate ankryins. Immunofluorescence microscopy showed that the ankryin-like protein is co-distributed with the myoplasm throughout development. It is restricted to a thin layer under the plasma membrane in unfertilised eggs, undergoes ooplasmic segregation to the posterior pole of the zygote after fertilisation, and is distributed to the tail muscle cells during cleavage and embryogenesis. After gastrulation and neurulation, lower levels of the ankryin-like protein, presumably of zygotic origin, were observed in brain cells and in the apical margin of epidermal cells. The ankryin-like protein was also localised in the myoplasm in eggs and embryos of another indirect developing species, Halocynthia roretzi. The ankryin-like protein may link the cytoskeleton with the plasma membrane in ascidian eggs, as it does in vertebrate erythrocytes. In contrast to A. ceratodes and H. roretzi, which are members of the families Ascidiidae and Pyuridae respectively, the pattern of ankryin-like protein expression was changed in five species in the family Molgulidae. These molgulid ascidians exhibit either indirect or direct development, and eggs of the direct developing species have lost or modified the myoplasm. The ankryin-like protein was present in young oocytes but failed to persist during oogenesis and disappeared in mature eggs and embryos of these molgulid species. The change in ankryin-like protein expression may be a preadaptation for loss of the myoplasm and the evolution of direct development.

Animals↗
PubMed1993

Novel genes expressed differentially in ascidians with alternate modes of development.

We have used a subtractive procedure to isolate cDNA clones encoding genes expressed differentially in ascidian species with alternate modes of development. The ascidians used in this study were Molgula occulta, which develops a tailed (urodele) larva, and Molgula occulta, which develops a tailless (anural) larva. Two of the identified clones, Uro-2 and Uro-11, are described. Southern blots show that the Uro-2 and Uro-11 genes are present in both species, but the corresponding mRNAs are expressed preferentially in the urodele species. In situ hybridization showed that Uro-2 and Uro-11 transcripts accumulate in small oocytes during oogenesis. The maternal Uro-2 and Uro-11 transcripts were distributed throughout the oocyte cytoplasm. Transcript concentrations declined during vitellogenesis, but mature eggs still contain detectable levels of Uro-2 and Uro-11 mRNA. After fertilization, the maternal Uro-2 and Uro-11 transcripts were localized in the ectoplasm of uncleaved zygotes and mostly entered the ectoderm cells during cleavage. The Uro-2 gene appears to produce only maternal transcripts. In contrast, the Uro-11 gene may also produce zygotic transcripts, which accumulate between gastrulation and neurulation in posterior epidermis, neural and tail muscle cells. Zygotic expression of the Uro-11 gene was not detected in embryos of the anural species. The deduced amino acid sequences of the Uro-2 and Uro-11 cDNAs suggest that they encode novel basic proteins with distinctive structural features. The predicted Uro-2 protein contain, a leucine zipper motif, suggesting that it may dimerize with another protein. The predicted Uro-11 protein contains a nuclear localization signal, a region with similarity to part of the DNA-binding motif in the bacterial histone-like HU and IHF proteins, 12 repeats of the proposed DNA-binding motif S(T)PXX, and a potential zinc finger of the C6 or C6H2 class, suggesting that it may be a DNA-binding protein. The Uro-2 and Uro-11 proteins are candidates for regulatory factors involved in the evolutionary transition from urodele to anural development.

Amino Acid Sequence↗
PubMed1992

Evolution of alternate modes of development in ascidians.

Ascidians have evolved alternate modes of development in which the conventional tadpole larva is remodeled or eliminated. Adultation, the precocious development of adult features in the larval head, is caused by superimposing the larval and adult differentiation programs. Caudalization, the addition of muscle cells to the larval tail, is caused by enhancing muscle induction or increasing the number of muscle cell divisions before terminal differentiation. Adultation and caudalization are correlated with increased egg size, suggesting dependence on maternal processes. Anural development, the elimination of the larval stage, is caused by maternal and zygotic events resulting in abbreviation and deletion of larval developmental programs. An example of a maternal change in anural species is the modification of the egg cytoskeleton during oogenesis, whereas a zygotic change may involve altered cell interactions during embryogenesis. Interspecific hybridization experiments suggest that some aspects of anural development may be caused by loss-of-function mutations. The dissociation of developmental programs is a key process in changing the mode of development in ascidians.

Animals↗
PubMed1992

Factors necessary for restoring an evolutionary change in an anural ascidian embryo.

The ascidian Molgula oculata has a tailed (or urodele) larva, whereas Molgula occulta develops directly via a tailless (or anural) embryo. Interspecific hybrid embryos produced by fertilizing M. occulta eggs with M. oculata sperm (M. occulta x M. oculata hybrids) can develop urodele larval structures, including a brain pigment cell and a short tail containing a small notochord. Development of larval features differs in individual M. occulta clutches: some eggs develop into hybrids with both a brain pigment cell and a tail, some into hybrids with either a brain pigment cell or a tail, and others into hybrids without urodele features. The expression of a 58-kDa protein (p58), which is present in eggs and embryos of urodele ascidians but lacking in those of most anural species, also varies in expression between different clutches of M. occulta eggs. Western blot and immunofluorescence studies show that p58 expression is correlated with the ability of hybrid embryos to express urodele features. For example, clutches of M. occulta eggs containing relatively high levels of p58 produce many hybrids with both a brain pigment cell and a tail. Differential expression of p58 occurs during oogenesis in M. occulta individuals: p58 is found at similar levels in previtellogenic oocytes, but in some animals it disappears during vitellogenesis, while in others it persists throughout oogenesis and is present in mature eggs. When M. occulta eggs are extracted with Triton X-100, p58 remains in the detergent-insoluble fraction, suggesting that it is associated with the cytoskeleton. In most unfertilized M. occulta eggs, p58 is uniformly distributed, but after fertilization it is localized in the uncleaved zygote and then concentrated in embryonic ectoderm, notochord, and muscle lineage cells. Despite containing high levels of p58, gynogenetic hybrid embryos, produced by fertilizing M. occulta eggs with uv-irradiated M. oculata sperm, develop into hybrids without a brain pigment cell or a tail. The results suggest that both a functional paternal genome and p58 are necessary for restoration of larval features in M. occulta x M. oculata hybrids. The cytoskeletal complex containing p58 may mediate the localization of key maternal factors in the egg or may be involved in cellular interactions during embryogenesis which are responsible for development of urodele cell fates.

Animals↗
PubMed1992

Multiple actin genes encoding the same alpha-muscle isoform are expressed during ascidian development.

Ascidian embryos develop rapidly into tadpole larvae containing striated tail muscle cells. We have isolated and characterized five actin cDNA clones from a Styela clava tailbud-stage library. The nucleotide sequences of these clones and genomic Southern blot analysis indicate that they represent at least four different muscle actin genes, which are designated ScTb1, ScTb24, ScTb30, and ScTb12/34. The derived protein sequences of these genes indicate that they encode the same alpha-muscle actin which has features related to each of the three different classes of vertebrate alpha-muscle actins. Northern and in situ hybridization with probes prepared from the 3' untranslated region (UTR) of several of the ScTb clones showed that these muscle actin genes are expressed in different temporal and spatial patterns during development. ScTb1 was detected in eggs, embryos, and adults, ScTb24 and ScTb12/34 were detected in embryos and adults, and ScTb30 was detected only in embryos. The maternal transcripts disappeared shortly after fertilization and zygotic mRNAs were first detected during gastrulation and continued to accumulate during subsequent tail muscle differentiation. ScTb30 mRNA, which is expressed in the embryo, peaks during the tailbud stage and is present at low levels in the tadpole larva. In contrast, ScTb1, ScTb24, and ScTb12/34 mRNAs, which are expressed in embryos and adults, peak during the late tailbud stage and are present in substantial quantities in the larva. The ScTb24 gene was detected only in tail muscle cells, whereas the ScTb30 gene was detected in embryonic tail muscle, mesenchyme, epidermal, and neural cells. The ScTb24 mRNA also accumulates primarily in vascular tissue in the branchial sac and mantle of adults. The existence of a gene family encoding the same alpha-muscle actin isoform is unique among the chordates and may function to maximize muscle actin production during the rapid differentiation phase of ascidian larval muscle cells.

Actins↗
PubMed1992

A gastrulation center in the ascidian egg.

A gastrulation center is described in ascidian eggs. Extensive cytoplasmic rearrangements occur in ascidian eggs between fertilization and first cleavage. During ooplasmic segregation, a specific cytoskeletal domain (the myoplasm) is translocated first to the vegetal pole (VP) and then to the posterior region of the zygote. A few hours later, gastrulation is initiated by invagination of endoderm cells in the VP region of the 110-cell embryo. After the completion of gastrulation, the embryonic axis is formed, which includes induction of the nervous system, morphogenesis of the larval tail and differentiation of tail muscle cells. Microsurgical deletion or ultraviolet (UV) irradiation of the VP region during the first phase of myoplasmic segregation prevents gastrulation, nervous system induction and tail formation, without affecting muscle cell differentiation. Similar manipulations of unfertilized eggs or uncleaved zygotes after the second phase of segregation have no effect on development, suggesting that a gastrulation center is established by transient localization of myoplasm in the VP region. The function of the gastrulation center was investigated by comparing protein synthesis in normal and UV-irradiated embryos. About 5% of 433 labelled polypeptides detected in 2D gels were affected by UV irradiation. The most prominent protein is a 30 kDa cytoskeletal component (p30), whose synthesis is abolished by UV irradiation. p30 synthesis peaks during gastrulation, is affected by the same UV dose and has the same UV-sensitivity period as gastrulation. However, p30 is not a UV-sensitive target because it is absent during ooplasmic segregation, the UV-sensitivity period. Moreover, the UV target has the absorption maximum of a nucleic acid rather than a protein. Cell-free translation studies indicate that p30 is encoded by a maternal mRNA. UV irradiation inhibits the ability of this transcript to direct p30 synthesis, indicating that p30 mRNA is a UV-sensitive target. The gasturlation center may function by sequestration or activation of maternal mRNAs encoding proteins that function during embryogenesis.

Animals↗
PubMed1991

An evolutionary change in the muscle lineage of an anural ascidian embryo is restored by interspecific hybridization with a urodele ascidian.

Anural ascidians do not develop into a conventional tailed larva with differentiated muscle cells, however, embryos of some anural ascidian species retain the ability to express acetylcholinesterase (AChE) in a vestigial muscle cell lineage. This study examines the number of AChE-positive cells that develop in the anural ascidian Molgula occulta relative to that in the closely related urodele (tailed) species, Molgula oculata. Histochemical assays showed that M. oculata embryos develop 36 to 38 AChE-positive cells, consistent with the number of tail muscle cells expressed in other urodele ascidians. In contrast, M. occulta embryos develop a mean of only 20 AChE-positive cells in their vestigial muscle lineage. Cleavage-arrested embryos of the anural species express AChE only in B-line blastomeres, showing that the vestigial muscle lineage cells are derived from the primary muscle lineage. Less than the expected number of AChE-positive B-line cells develop in cleavage-arrested anural embryos, however, implying that the allocation of primary muscle lineage cells is decreased. Eggs of the anural species can be fertilized with sperm of the urodele species resulting in the development of some larvae that contain a short tail and/or a brain melanocyte, specific features of urodele larvae. The typical urodele number of AChE-positive cells is restored in some of these hybrid embryos. Both primary and secondary muscle lineages are restored because cleavage-arrested hybrid embryos develop more AChE-positive cells in the B-line blastomeres and supernumerary AChE-positive cells in the A-line blastomeres. Hybrid embryos that develop the urodele complement of AChE-positive cells also form a tail and/or a brain melanocyte showing that restoration of muscle lineage cells is coupled to the development of other urodele features. AChE expression occurred in anural embryos with disorganized or dissociated blastomeres, indicating that AChE expression is determined autonomously. It is concluded that an evolutionary change in the allocation of larval muscle lineage cells occurs during development of the anural ascidian M. occulta which can be restored by interspecific hybridization with the urodele ascidian M. oculata.

Acetylcholinesterase↗
PubMed1991

Identification of a cytoskeletal protein localized in the myoplasm of ascidian eggs: localization is modified during anural development.

The myoplasm of ascidian eggs is a localized cytoskeletal domain that is segregated to presumptive larval tail muscle cells during embryonic development. We have identified a cytoskeletal protein recognized by a vertebrate neurofilament monoclonal antibody (NN18) which is concentrated in the myoplasm in eggs and embryos of a variety of ascidian species. The NN18 antigen is localized in the periphery of unfertilized eggs, segregates with the myoplasm after fertilization, and enters the larval tail muscle cells during embryonic development. Western blots of one-dimensional and two-dimensional gels showed that the major component recognized by NN18 antibody is a 58 x 10(3) Mr protein (p58), which exists in at least three different isoforms. The enrichment of p58 in the Triton X-100-insoluble fraction of eggs and its reticular staining pattern in eggs and embryos suggests that it is a cytoskeletal protein. In subsequent experiments, p58 was used as a marker to determine whether changes in the myoplasm occur in eggs of anural ascidian species, i.e. those exhibiting a life cycle lacking tadpole larvae with differentiated muscle cells. Although p58 was localized in the myoplasm in eggs of four urodele ascidian species that develop into swimming tadpole larvae, this protein was distributed uniformly in eggs of three anural ascidian species. The eggs of two of these anural species contained the actin lamina, another component of the myoplasm, whereas the third anural species lacked the actin lamina. There was no detectible localization of p58 after fertilization or segregation into muscle lineage cells during cleavage of anural eggs. NN18 antigen was uniformly distributed in pre-vitellogenic oocytes and then localized in the perinuclear zone during vitellogenesis of urodele and anural ascidians. Subsequently, NN18 antigen was concentrated in the peripheral cytoplasm of post-vitellogenic oocytes and mature eggs of urodele, but not anural, ascidians. It is concluded that the myoplasm of ascidian eggs contains an intermediate filament-like cytoskeletal network which is missing in anural species that have modified or eliminated the tadpole larva.

Actins↗
PubMed1990

Temporal and spatial expression of a cytoskeletal actin gene in the ascidian Styela clava.

We have cloned and characterized the temporal and spatial expression of ScCA15, a cDNA clone encoding an actin gene in the ascidian Styela clava. The partial nucleotide and derived amino acid sequences of this singlecopy gene suggest that it is a cytoskeletal actin. Northern analysis shows that ScCA15 corresponds to a 1.8-kb mRNA that is transcribed during oogenesis, during embryonic development, and in the adult. In situ hybridization shows that maternal ScCA15 mRNA is distributed uniformly in the cytoplasm of the oocyte and unfertilized egg. During the period of ooplasmic segregation following fertilization, however, ScCA15 mRNA appears to be translocated into the ectoplasm, a specialized cytoplasmic region of the egg. During the early cleavages, the ectoplasmic transcripts are partitioned to ectodermal cells in the animal hemisphere, which are precursors of the epidermis and nervous system of the larva. Maternal ScCA15 mRNA is degraded just before gastrulation and replaced by zygotic transcripts which begin to accumulate between the neurula and mid-tailbud stages. Zygotic ScCA15 mRNA accumulates primarily in the epidermal and neural cells, although lower levels of these transcripts may also be present in tail muscle cells. These results show that two mechanisms are used to concentrate ScCA15 mRNA in the ectodermal cells during development: 1) localization and differential segregation of maternal transcripts and 2) specific expression of the ScCA15 gene. ScCA15 mRNA is detected by in situ hybridization in the testes, ovaries, alimentary tract, and endostyle of adults. In the testes, ScCA15 mRNA is present in developing sperm, whereas in the ovary, these transcripts are present in the germinal epithelium and developing oocytes. In the alimentary tract, ScCA15 mRNA is confined to the gastric epithelium of the esophagus, stomach, and intestine. Since the ScCA15 gene is expressed in embryonic and adult tissues that are undergoing rapid cell division, this actin is likely to function in some aspect of cell proliferation.

Actins↗
PubMed1990

Ultraviolet irradiation during ooplasmic segregation prevents gastrulation, sensory cell induction, and axis formation in the ascidian embryo.

The effect of ultraviolet (uv) light on embryonic development was examined in the ascidian Styela clava. uv irradiation (3.0 x 10(-3) J mm-2) of the entire surface of fertilized eggs during ooplasmic segregation prevented gastrulation, sensory cell induction, and embryonic axis formation. The uv-irradiated embryos completed ooplasmic segregation and cleaved normally, but vegetal blastomeres did not invaginate at the beginning of gastrulation, sensory cells in the larval brain did not develop tyrosinase or melanin pigment, and the larval tail did not develop. Endoderm, epidermis, and muscle cells differentiated in the uv-irradiated embryos, however, as evidenced by expression of endodermal alkaline phosphatase (AP), an epidermal-specific antigen, and alpha-actin, myosin heavy chain, and acetylcholinesterase (AChE) in muscle cells. Higher doses of uv light (6.0-9.0 x 10(-3) J mm-2) suppressed expression of the epidermal antigen and muscle cell markers, whereas the development of endodermal AP was insensitive. Irradiation at various times between fertilization and the 16-cell stage revealed that gastrulation, sensory cell differentiation, and axis formation are sensitive to uv light only during ooplasmic segregation. Irradiation of restricted regions of the zygote during ooplasmic segregation showed that the uv-sensitive components are localized in the vegetal hemisphere. The absorption characteristics of the uv-sensitive components suggest that they are nucleic acids. The results show that uv-sensitive components that specify gastrulation, sensory cell induction, and embryonic axis formation are localized in the vegetal hemisphere of Styela eggs.

Acetylcholinesterase↗
PubMed1990

An ultraviolet-sensitive maternal mRNA encoding a cytoskeletal protein may be involved in axis formation in the ascidian embryo.

Ultraviolet (uv) irradiation of the vegetal hemisphere of fertilized eggs during ooplasmic segregation inhibits subsequent gastrulation and axis formation in ascidian embryos. The molecular basis of this phenomenon was investigated in by comparing in vivo protein synthesis and in vitro mRNA translation in normal and uv-irradiated embryos of the ascidian Styela clava. Analysis of protein synthesis by [35S]methionine incorporation, two-dimensional (2D) gel electrophoresis, and autoradiography showed that only 21 (or about 5%) of 433 labeled polypeptides were missing or decreased in labeling intensity in uv-irradiated embryos. The most prominent of these was a 30,000 molecular weight (pI 6.0) polypeptide (p30). Extraction of gastrulae with the nonionic detergent Triton X-100 showed that p30 is retained in the detergent insoluble residue, suggesting that it is associated with the cytoskeleton. Several lines of evidence suggest that p30 may be involved in axis formation. First, p30 labeling peaks during gastrulation, when the embryonic axis is being established. Second, axis formation and p30 labeling are abolished by the same threshold uv dose, which is distinct from that required to inactivate muscle cell development. Third, the uv sensitivity period for abolishing p30 labeling and axis formation are both restricted to ooplasmic segregation. In vitro translation of egg RNA followed by 2D gel electrophoresis and autoradiography of the protein products showed that p30 is encoded by a maternal mRNA. The translation of p30 mRNA was abolished by uv irradiation of fertilized eggs during ooplasmic segregation suggesting that this message is a uv-sensitive target. The results are consistent with the hypothesis that uv irradiation blocks gastrulation and axis formation by inhibiting the translation of maternal mRNA localized in the vegetal hemisphere of the fertilized egg.

Acetylcholinesterase↗
PubMed1990

Interspecific hybridization between an anural and urodele ascidian: differential expression of urodele features suggests multiple mechanisms control anural development.

Anural development in the ascidian Molgula occulta was examined using tissue-specific markers and interspecific hybridization. Unlike most ascidians, which develop into a swimming tadpole larva (urodele development), M. occulta eggs develop into a tailless slug-like larva (anural development) which metamorphoses into an adult. M. occulta embryos show conventional early cleavage patterns, gastrulation, and neurulation, but then diverge from the urodele developmental mode during larval morphogenesis. M. occulta larvae do not contain a pigmented sensory cell in their brain or form a tail with differentiated notochord and muscle cells. As shown by in situ hybridization with cloned probes and analysis of in vitro translation products, M. occulta embryos do not accumulate high levels of alpha actin or myosin heavy chain mRNA. In contrast, acetylcholinesterase is expressed in muscle lineage cells, indicating that various muscle cell features are differentially suppressed. M. occulta embryos also lack tyrosinase activity, suggesting that suppression of brain pigment cell differentiation occurs at an early step in development. M. occulta eggs fertilized with sperm from Molgula oculata (a closely related urodele species) develop into hybrid larvae exhibiting some of the missing urodele features. Some hybrid embryos develop tyrosinase activity and differentiate a brain pigment cell and a short row of notochord cells, and form a short tail. These urodele features appeared together or separately in different hybrid embryos suggesting that they develop by independent mechanisms. In contrast, alpha actin and myosin heavy chain mRNA accumulation was not enhanced in hybrid embryos. These results suggest that multiple mechanisms control anural development.

Animals↗