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M Jamrich

Publications and source records attributed to M Jamrich.

At least 37 records · Page 2Linked to original sources
PubMed1994

Expression of the LIM class homeobox gene Xlim-1 in pronephros and CNS cell lineages of Xenopus embryos is affected by retinoic acid and exogastrulation.

The LIM class homeobox gene Xlim-1 is expressed in Xenopus embryos in the lineages leading to (i) the notochord, (ii) the pronephros, and (iii) certain cells of the central nervous system (CNS). In its first expression phase, Xlim-1 mRNA arises in the Spemann organizer region, accumulates in prechordal mesoderm and notochord during gastrulation, and decays in these tissues during neurula stages except that it persists in the posterior tip of the notochord. In the second phase, expression in lateral mesoderm begins at late gastrula, and converges to the pronephros at tailbud stages. Expression in a central location of the neural plate also initiates at late gastrula, expands anteriorly and posteriorly, and becomes established in the lateral regions of the spinal cord and hindbrain at tailbud stages. Thus Xlim-1 expression precedes morphogenesis, suggesting that it may be involved in cell specification in these lineages. Enhancement of Xlim-1 expression by retinoic acid (RA) was first detectable in the dorsal mesoderm at initial gastrula. During gastrulation and early neurulation, RA strongly enhanced Xlim-1 expression in all three lineages and also expanded its expressing domains; this overexpression correlated well with RA phenotypes such as enlarged pronephros and hindbrain-like structure. Exogastrulation reduced Xlim-1 expression in the lateral mesoderm and ectoderm but not in the notochord, suggesting that the second phase of Xlim-1 expression requires mesoderm/ectoderm interactions. RA treatment of exogastrulae did not revert this reduction.

Animals↗
PubMed1993

Expression of a Xenopus Distal-less homeobox gene involved in forebrain and cranio-facial development.

Homeobox-containing genes are thought to perform essential functions in the process of pattern formation in vertebrates and invertebrates. They provide cells with positional information critical for normal embryonic development. Since most of the identified homeobox genes in Xenopus seem to provide positional information for the development of the trunk, we have concentrated on genes that may be specifically involved in the formation of the head region. Using a polymerase chain reaction strategy we have searched for Xenopus homeobox-containing genes that might provide positional cues for correct development of the brain. In this paper we report the identification and cloning of a novel gene that by homology appears to be a member of the Distal-less homeobox gene family. We show that its temporal expression patterns in the cement gland, neural crest derived visceral arches, retina and forebrain, while quite diverse, does suggest shared developmental features which may be required for correct craniofacial development and the regionalization of the Xenopus brain. Furthermore, expression of this gene at later stages is primarily restricted to the tadpole forebrain suggesting that the Distal-less gene product continues to play a role after the initial brain patterning is complete.

Amino Acid Sequence↗
PubMed1993

Comparative analysis of the expression and oncogenic activities of Xenopus c-, N-, and L-myc homologs.

A polymerase chain reaction-based cloning strategy allowed for the isolation of two distinct Xenopus L-myc genes, as well as previously isolated xc- and xN-myc genes, thus demonstrating that these three well-defined members of the mammalian myc gene family are present in lower vertebrates as well. Comparison of the Xenopus and mammalian Myc families revealed a high degree of structural relatedness at the gene and protein levels; this homology was consistent with the ability of the xc-myc1 and xN-myc1 genes to function as oncogenes in primary mammalian cells. In contrast, the xL-myc1 gene was found to be incapable of transforming rat embryo fibroblast cells, and this inactivity may relate to localized but significant differences in its putative transactivation domain. Analysis of xc-, xN-, and xL-myc gene expression demonstrated that (i) all three genes were highly expressed during oogenesis and their transcripts accumulated as abundant maternal mRNAs, (ii) each gene exhibited a distinctive pattern of expression during embryogenesis and in adult tissues, and (iii) the xL-myc1 and xL-myc2 genes were coordinately expressed in the maternal and zygotic genomes. The markedly high expression of the Xenopus myc gene family in differentiated tissues, such as the central nervous system and kidney, contrasts sharply with the low levels observed in mammalian adult tissues. These differences may reflect unique functions of the Myc family proteins in processes specific to amphibians, such as tissue regeneration.

Amino Acid Sequence↗
PubMed1992

The LIM domain-containing homeo box gene Xlim-1 is expressed specifically in the organizer region of Xenopus gastrula embryos.

A novel cysteine-rich motif, named LIM, has been identified in the homeo box genes lin-11, Isl-1, and mec-3; the mec-3 and lin-11 genes determine cell lineages in Caenorhabditis elegans. We isolated LIM class homeo box genes from Xenopus laevis that are closely related to lin-11 and mec-3 in the LIM and homeo domains. This paper deals with one of these genes, Xlim-1. Xlim-1 mRNA is found at low abundance in the unfertilized egg, has a major expression phase at the gastrula stage, decreases, and rises again during the tadpole stage. In adult tissues the brain shows the highest abundance, by far, of Xlim-1 mRNA. The maternal and late expression phases of the Xlim-1 gene suggest that it has multiple functions at different stages of the Xenopus life cycle. In the gastrula embryo, Xlim-1 mRNA is localized in the dorsal lip and the dorsal mesoderm, that is, in the region of Spemann's organizer. Explant experiments showed that Xlim-1 mRNA is induced by the mesoderm-inducer activin A and by retinoic acid, which is not a mesoderm inducer but affects patterning during Xenopus embryogenesis; application of activin A and retinoic acid together results in synergistic induction. The structure, inducibility, and localized expression in the organizer of the Xlim-1 gene suggest that it has a role in establishing body pattern during gastrulation.

Activins↗
PubMed1992

A novel, activin-inducible, blastopore lip-specific gene of Xenopus laevis contains a fork head DNA-binding domain.

The organizer region, or dorsal blastopore lip, plays a central role in the initiation of gastrulation and the formation of the body axis during Xenopus development. A similar process can also be induced in ectodermal explants by activin or by injection of activin mRNA into embryos. We have searched early embryo-specific cDNA libraries for genes containing the fork head box sequence that encodes a DNA-binding domain similar to that of the Drosophila homeotic gene fork head and rat hepatocyte nuclear factor HFN3 beta. These genes were subsequently tested for expression in the organizer region of blastula/gastrula-stage embryos as well as inducibility by activin. Our effort resulted in the isolation of a gene, XFKH1, that is primarily expressed in the dorsal blastopore lip of early gastrulae and is inducible by activin. At later stages it is expressed in the notochord and neural floor plate. Because of its spatial and temporal expression pattern, as well as its inducibility by activin, this gene is a good candidate to have a regulatory function in the initial processes of axis formation in Xenopus laevis embryos.

Activins↗
PubMed1989

Differential gene expression in the anterior neural plate during gastrulation of Xenopus laevis.

We have isolated three cDNA clones that are preferentially expressed in the cement gland of early Xenopus laevis embryos. These clones were used to study processes involved in the induction of this secretory organ. Results obtained show that the induction of this gland coincides with the process of neural induction. Genes specific for the cement gland are expressed very early in the anterior neural plate of stage-12 embryos. This suggests that the anteroposterior polarity of the neural plate is already established during gastrulation. At later stages of development, two of the three genes have secondary sites of expression. The expression of these genes can be induced in isolated animal caps by incubation in 10 mM-NH4Cl, a treatment that is known to induce cement glands.

Animals↗
PubMed1988

Accumulation and decay of DG42 gene products follow a gradient pattern during Xenopus embryogenesis.

The DG42 gene is expressed during a short window during embryogenesis of Xenopus laevis. The mRNA for this gene can be first detected just after midblastula, peaks at late gastrula, and decays by the end of neurulation. The sequence of the DG42 cDNA and genomic DNA predicts a 70,000-Da protein that is not related to any other known protein. Antibodies prepared against portions of the DG42 open reading frame that had been expressed in bacteria detected a 70,000-Da protein in the embryo with a temporal course of appearance and decay that follows that of the RNA by several hours. Localization of the mRNA in dissected embryos and immunohistochemical detection of the protein showed that DG42 expression moves as a wave or gradient through the embryo. The RNA is first detected in the animal region of the blastula, and by early gastrula is found everywhere except in the outer layer of the dorsal blastopore lip. By midgastrula DG42 protein is present in the inner ectodermal layer and the endoderm; it disappears from dorsal ectoderm as the neural plate is induced and later decays in a dorsoventral direction. The last remnants of DG42 protein are seen in ventral regions of the gut at the tailbud stage.

Animals↗
PubMed1988

Gene expression in amphibian embryogenesis.

The study of molecular events during the embryogenesis of Xenopus laevis has advanced as a result of the availability of molecular markers, i.e., nucleic acid and antibody probes for genes that are expressed in a temporally and spatially regulated fashion during development. In this article we summarize results on the localized expression of keratin genes and on the reconstruction of regulated transcription of the gastrula/neurula-specific DG42 gene. Furthermore, we discuss experiments that investigate molecular events during mesoderm induction and provide information on the nature of the inducing principle.

Animals↗
PubMed1988

Xenopus endo B is a keratin preferentially expressed in the embryonic notochord.

Screening of a cDNA library from neurula stage Xenopus laevis for notochord-specific sequences led to the isolation of a cDNA clone, XK endo B (Xenopus keratin endo B), which encodes a nonepidermal type I keratin. In situ and Northern blot hybridizations indicate that expression of XK endo B RNA is concentrated in the notochord, whereas expression in the endoderm is 5-10 times lower. XK endo B mRNA is present in the oocyte and increases from late gastrula. Accumulation peaks by late neurula and is greatly reduced by the tadpole stage; in the adult, a low level of XK endo B RNA is present in the liver. XK endo B shows sequence homology to mouse endo B; genomic Southern blots show that XK endo B is the most similar sequence to mouse endo B in the Xenopus genome, and vice versa, indicating that XK endo B and mouse endo B are homologs. The use of endo B as a marker and the germ layer derivation of the notochord are discussed in light of these results.

Amino Acid Sequence↗
PubMed1987

Cell-type-specific expression of epidermal cytokeratin genes during gastrulation of Xenopus laevis.

Analysis of the spatial pattern of expression of embryo-specific epidermal cytokeratin genes in Xenopus laevis shows earliest activity in the animal pole cells of stage-9 blastulae. These genes are transcribed predominantly in the epithelial or outer ectoderm, to a lesser extent in the sensorial or inner ectoderm, and at low levels if at all in other regions of the embryo. In the early gastrula the entire ectoderm, including preneural and preepidermal regions, expresses cytokeratin mRNAs; accumulation of these mRNAs in preneural cells is terminated after contact is made with involuting chordamesoderm. On the basis of this and earlier work (Sargent et al. 1986) we suggest that the pattern of expression of cytokeratin genes in frog embryogenesis is based on prelocalized components modulated by the inductive influence of involuting chordamesoderm. The cytokeratin proteins are deposited in the form of filamentous networks in both layers of the epidermis. In the epithelial layer, a much denser mesh of filaments is facing the outside of the embryo. This polarity is established at the onset of the polymerization of these filaments. Thus, intraembryonic and intracellular localization of keratin gene expression and protein deposition is established at the onset of activation of these genes.

Animals↗
PubMed1986

Cell interactions and the control of gene activity during early development of Xenopus laevis.

During embryonic development, regulation of the zygotic genome may be mediated by inductive interactions and by cell-autonomous inheritance of informational material from the egg; we have studied certain aspects of such regulatory events in Xenopus laevis. Embryos cultured in Ca2+/Mg2+-free medium can be dissociated and dispersed, eliminating cell-cell contact and thus precluding inductive interactions. Such manipulations revealed that activation of the muscle-specific alpha-actin genes is absolutely dependent upon cell contacts. Conversely, the endoderm-specific DG42 gene and the ectoderm-specific DG81 cytokeratin gene are activated in embryo cells dispersed throughout blastula stages and therefore appear to be controlled by inherited factors. Nevertheless, abnormal cell arrangements may prevent expression of the cytokeratin gene, suggesting that animal pole cells can be diverted from their normal ectodermal fate by inductive contact with vegetally derived cells. The interactions required for alpha-actin induction and inhibition of cytokeratin expression are independent of strong adhesion between embryonic cells mediated by high concentrations of divalent cations.

Actins↗
PubMed1985

Gene expression in Xenopus embryogenesis.

This article considers some aspects of the storage of macromolecules in the oocyte of Xenopus laevis and the activation of previously unexpressed genes during early embryogenesis. The large quantity and complex nature of poly(A)+ RNA accumulated in the egg provides the cleavage embryo with a supply of mRNA sufficient to sustain protein synthesis for several hours of development. Onset of gene activity at the midblastula transition (MBT) leads to the synthesis and accumulation of molecules of various RNA classes, including tRNAs, rRNAs, mRNAs and mitochondrial RNAs. At gastrulation the poly(A)+ RNA population is still qualitatively similar to that of the egg but some sequences not present in egg RNA have accumulated by this time. Through the use of a subtractive cDNA cloning procedure we have prepared a library of sequences that represent genes activated for the first time between MBT and gastrula. A study of several of these cDNA clones suggests that genes in this class are restricted in their activity to embryonic and tadpole stages.

Animals↗
PubMed1984

The rare transcripts of interrupted rRNA genes in Drosophila melanogaster are processed or degraded during synthesis.

About 50% of the ribosomal transcription units in females of the bobbed 8 mutant of Drosophila melanogaster contain an intervening sequence of 5 kb in the 28S region of the gene. We analysed the transcription of ribosomal genes in this mutant using electron microscopy and found that the majority of the active ribosomal transcription units in larval fat bodies and guts are not long enough to contain the 5-kb intervening sequence; only approximately 1% of active transcription units have a length consistent with the presence of the 5-kb intervening sequence. Transcription units of this length show an interrupted gradient of nascent RNA fibril lengths indicative of processing or degradation during transcription. The position of the discontinuity in RNA length coincides with the position of the intervening sequence. This observation suggests that even though RNA polymerase may infrequently transcribe an entire interrupted gene, the process does not result in a full-length RNA.

Animals↗
PubMed1984

Histone RNA in amphibian oocytes visualized by in situ hybridization to methacrylate-embedded tissue sections.

We present an in situ hybridization method for detecting cellular RNAs in tissue sections using methacrylate as the embedding medium. The technique offers the advantage of superior morphological preservation compared with previously published procedures. Since sections can be cut 1 micron or less in thickness, full advantage is taken of the short path length of 3H electrons. Applying this procedure to developing amphibian oocytes, we investigated the accumulation and localization of RNA complementary to the histone genes and their adjacent spacers. Histone RNA begins to accumulate in the cytoplasm of late pachytene-early diplotene oocytes, rapidly reaching a maximum concentration during Dumont stage 1. After this stage the concentration of histone RNA declines. RNA transcribed from histone coding regions is located almost exclusively in the cytoplasm of oocytes. Transcripts of the spacer regions, which are known to be synthesized on oocyte lampbrush chromosomes, do not accumulate in the oocytes. [3H]RNA complementary to U2 small nuclear RNA, used in these experiments as a control, hybridized predominantly to the nucleus of the oocytes.

Animals↗
PubMed1984

Transcription of a long, interspersed, highly repeated DNA element in Xenopus laevis.

We have analyzed the transcription of 1723, a long, repeated DNA element that is interspersed in the genome of Xenopus laevis (B. K. Kay and I. B. Dawid (1983) J. Mol. Biol. 170, 583-596). We have detected RNA homologous to 1723 in total cellular RNA from ovaries, embryos, liver, and cultured kidney cells. Transcripts from both strands of the element are present at similar concentrations in these different RNA preparations. In oocytes, approximately 100 pairs of lampbrush chromosome loops are active in the transcription of 1723 elements. The abundance of 1723 RNA increases during embryogenesis, with the highest level reached at the tadpole stage. From cellular fractionation studies, we conclude that 1723 transcripts are largely limited to the nucleus.

Animals↗
PubMed1983

Transcription of repetitive sequences on Xenopus lampbrush chromosomes.

We reinvestigated the lampbrush chromosomes of Xenopus laevis and found them well suited for the study or transcription by in situ hybridization to nascent RNA transcripts. Using this technique, we analyzed the transcription of three repetitive sequences that do not show any sequence homology and that differ in their degree of interspersion. We found that they are located on different parts of the chromosomes: two are clustered, one is interspersed. All three of these sequences are transcribed at the lampbrush chromosome stage and transcripts from both strands of each sequence can be detected. The amount of transcription is apparently not proportional to the number of copies of the repetitive sequence at a given chromosomal locus, suggesting that other sequences are involved in the regulation of their transcription.

Animals↗