The molecular organization of the β-globin complex of the deer mouse, Peromyscus maniculatus.
Molecular biology and evolution. 4:30-45. Abstract
Recombinant DNA clones have been isolated that contain 80 kb of the beta-globin complex from the deer mouse, Peromyscus maniculatus. Comparisons of this complex with that from the laboratory mouse, Mus domesticus (with an order 5'-Hbby, Hbb-bhO, Hbb-bhl, Hbb-bh2, Hbb-bh3, Hbb-bl, Hbb-b2 3') highlight organizational trends in the beta-globin complex since the two species diverged. Unlike other mammals studied thus far, the deer mouse possesses three adult genes. Partial sequence analysis indicates that each of the three adult genes is intact and hence may be functional. Hybridization of one of the two Mus pseudogenes, Hbb-bh3, to genomic blots from Peromyscus reveals that it has a homologous counterpart in Peromyscus. Homologous genes to the two gamma-like Mus genes, Hbb-bhO and Hbb-bhl, are also found in Peromyscus. The strong hybridization between the Hbb-bhl genes and significant nucleotide similarity between the Hbb-bhO genes suggest that both pairs are important for the ontogeny of these mice although no known product has been identified for the Hbb-bhO genes. The presence of Hbb-bhO and Hbb-bhl in Peromyscus suggests that the duplication that created this related gene set occurred before the two lineages diverged. A single gene for Hbb-y has been isolated from Peromyscus. The adult region in Peromyscus has undergone significant divergence from the same region in Mus, having three rather than two adult genes, the acquisition of at least 15 kb of extra DNA relative to Mus, and possibly the loss of the Hbb-bh2 pseudogene. The nonadult region of the complex, in contrast, contains the same set of genes apparently distributed over the same amount of DNA as in the Mus beta-globin complex. This observation suggests that the embryonic region of the complex is more evolutionarily stable than the adult region.
A transcript from a Drosophila pattern gene predicts a protein homologous to the transforming growth factor-β family.
Nature. 325:81-4. Abstract
The decapentaplegic gene complex (DPP-C) has been implicated in several events in pattern formation during Drosophila development. During embryogenesis, the DPP-C participates in the establishment of dorsal-ventral specification. Later, it is required for the correct morphogenesis of the imaginal disks, which will form much of the adult epidermis. We have undertaken a molecular analysis of the DPP-C to determine what role it plays in positional information. It appears to be a large genetic unit (greater than 40 kilobases (kb] consisting mostly of cis-regulatory information controlling the expression of a set of overlapping transcripts that differ at their 5' ends, but share the bulk of their transcribed sequences. Here, we describe the sequence analysis of two complementary DNAs comprising 4.0 kb of a 4.5-kb transcript. The C-terminus of the protein thereby deduced exhibits strong sequence homology (25-38% amino-acid identity) to the C-termini of a class of mammalian proteins that includes transforming growth factor-beta (TGF-beta), inhibin and Müllerian inhibiting substance (MIS). These proteins act on target cells to produce a variety of responses, such as stimulation or inhibition of cell division or differentiation. The homology suggests that the DPP-C protein contributes to correct morphogenesis as a secreted factor involved in the differential regulation of cell growth. This is the first report of a member of the TGF-beta gene family in a non-mammalian organism, and indicates that one or more members of this gene family existed before arthropod and vertebrate lineages diverged.
Genetic and biochemical analysis of TGFβ signal transduction.
Cytokine & growth factor reviews. 8:1-9. Abstract
TGF beta-like ligands are involved in many different developmental processes that pattern a variety of tissues in invertebrates and vertebrates. In the last few years, rapid progress has been made toward elucidating the developmental roles of the TGF beta-like pathways and identifying the novel components involved in transducing their signals, particularly the newly discovered Smads. This rapid progress has been the result of a synergy between classical genetic approaches and biochemical approaches, and this combined approach is likely to propel future understanding of the signaling pathway used by TGF beta.
Smads are the central component in transforming growth factor-β signaling.
Pharmacology & therapeutics. 78:47-52. Abstract
Until recently, little was known about how transforming growth factor (TGF)-beta signals are transduced to the nucleus. With the discovery of the Smad proteins initially in Drosophila and C. elegans, the unraveling of the pathway has begun. Nine different vertebrate members also have been reported, indicating that Smads are a conserved component of the TGF-beta pathway. Currently, there are three functional classes of Smads. Class I Smads are phosphorylated by TGF-beta receptors and move to the nucleus. The Class II Smads function with Class I Smads, while Class III Smads antagonize the function of Class I Smads. New evidence shows that Smads bind specific DNA sequences and induce transcription of downstream target genes, thus placing the Smads at the center of the TGF-beta signaling pathway.
Human BMP sequences can confer normal dorsal-ventral patterning in the Drosophila embryo.
Proceedings of the National Academy of Sciences of the United States of America. 90:2905-9. Abstract
The type beta transforming growth factor family is composed of a series of processed, secreted growth factors, several of which have been implicated in important regulatory roles in cell determination, inductive interactions, and tissue differentiation. Among these factors, the sequence of the DPP protein from Drosophila is most similar to two of the vertebrate bone morphogenetic proteins, BMP2 and BMP4. Here we report that the human BMP4 ligand sequences can function in lieu of DPP in Drosophila embryos. We introduced the ligand region from human BMP4 into a genomic fragment of the dpp gene in place of the Drosophila ligand sequences and recovered transgenic flies by P-element transformation. We find that this chimeric dpp-BMP4 transgene can completely rescue the embryonic dorsal-ventral patterning defect of null dpp mutant genotypes. We infer that the chimeric DPP-BMP4 protein can be processed properly and, by analogy with the action of other family members, can activate the endogenous DPP receptor to carry out the events necessary for dorsal-ventral patterning. Our evidence suggests that the DPP-BMP4 signal transduction pathway has been functionally conserved for at least 600 million years.
TGFβ superfamily signaling: notes from the desert.
Development (Cambridge, England). 134:3565-9. Abstract
The TGFbeta pathways play crucial roles in many developmental events, as well as contributing to many disease states. To provide a venue for both signaling and developmental research on TGFbeta, a FASEB-sponsored bi-annual meeting was initiated six years ago, the fourth of which was organized by Caroline Hill and Michael O'Connor and took place this July in Tucson, Arizona. The meeting highlighted major advances in our understanding of the structural and biochemical aspects of TGFbeta superfamily signaling, its intersection with other pathways, and its contribution to disease.
New developments for TGFβ.
Developmental cell. 1:343-9. Abstract
A recent FASEB meeting was held in Tucson, Arizona that encompassed TGFbeta superfamily signaling pathways and their roles in development. This review focuses on the developmental biology presented at the meeting.
TGFβ signaling pathways and human diseases.
Cancer metastasis reviews. 18:247-59. Abstract
Recent progress in deciphering the TGFbeta pathway has uncovered a new signaling molecule, the Smads, and with this finding now gives us insights into how TGFbeta-like signals are transmitted from outside the cell to the nucleus. As we learn more about how TGFbeta regulates normal development, we also are gaining insights into diseases that are caused by mis-regulation or mutation of various components of the signaling pathways.
TGF-β signaling, Smads, and tumor suppressors.
BioEssays : news and reviews in molecular, cellular and developmental biology. 20:382-90. Abstract
The transforming growth factor-beta (TGF-beta) superfamily is used throughout animal development for regulating the growth and patterning of many tissue types. During the past few years, rapid progress has been made in deciphering how TGF-beta signals are transduced from outside the cell to the nucleus. This progress is based on biochemical studies in vertebrate systems and a combination of genetic studies in Drosophila and Caenorhabditis elegans. These studies have identified a novel family of signaling proteins, the Smad family. Smads can act positively and be phosphorylated by TGF-beta-like receptors or can act negatively and prevent activation of the positively acting group. The positively acting Smads translocate to the nucleus, bind DNA, and act as transcriptional activators. Thus, genetic and biochemical studies suggest a very simple signaling pathway, in which Smads are the primary downstream participant.
Intracellular signaling: Fleshing out the TGFβ pathway.
Current biology : CB. 9:R408-11. Abstract
Recent studies of the intracellular signaling pathway initiated by ligands of the transforming growth factor beta (TGFbeta) family have provided new insights into how the receptors for such ligands phosphorylate their substrates - the Smads - and how signaling specificity is achieved.
The F-type 5' motif of mouse L1 elements: a major class of L1 termini similar to the A-type in organization but unrelated in sequence.
Nucleic Acids Res. 16:739-49. Abstract
It has previously been shown that the L1 family in the mouse (L1Md) contains two alternative 5' ends called the A- and F-type sequences (1,2). We show here that the F-type element is a major class of murine L1 elements and report on the details of organization of the 5' motif of these F-type elements. Although the A- and F-type 5' sequences share no detectable sequence homology the organization of an F-type 5' end is strikingly similar to that of an A-type. That is, the F-type 5' sequences consist of a tandem array of a small number of 206 bp monomers while the A-type 5' motif consists of a tandem array of 208 bp monomers. All of the A-type elements characterized to date have a truncated monomer at the 5' end of the array. Many of the F-type elements are also terminated at the 5' end by a truncated copy but unlike the A-type elements some F-type elements terminate with a monomer which is within a few nucleotides of being complete. In addition the F-type consensus sequence, in contrast to the A-type sequence, shows homology (70%) to the body of the L1Md starting at the position where the monomer joins the rest of the L1 element.
TGFβ-related pathways. Roles in Caenorhabditis elegans development.
Trends Genet. 16:27-33. Abstract
Genetic and molecular analysis in Caenorhabditis elegans has produced new insights into how TGF beta-related pathways transduce signals and the developmental processes in which they function. These pathways are essential regulators of dauer formation, body-size determination, male copulatory structures and axonal guidance. Here, we review the insights that have come from standard molecular genetic experiments and discuss how the recently completed genome sequence has contributed to our understanding of these pathways.
Caenorhabditis elegans pseudouridine synthase 1 activity in vivo: tRNA is a substrate, but not U2 small nuclear RNA.
The Biochemical journal. 372:595-602. Abstract
The formation of pseudouridine (Psi) from uridine is post-transcriptional and catalysed by pseudouridine synthases, several of which have been characterized from eukaryotes. Pseudouridine synthase 1 (Pus1p) has been well characterized from yeast and mice. In yeast, Pus1p has been shown to have dual substrate specificity, modifying uridines in tRNAs and at position 44 in U2 small nuclear RNA (U2 snRNA). In order to study the in vivo activity of a metazoan Pus1p, a knockout of the gene coding for the homologue of Pus1p in Caenorhabditis elegans was obtained. The deletion encompasses the first two putative exons and includes the essential aspartate that is required for activity in truA pseudouridine synthases. The locations of most modified nucleotides on small RNAs in C. elegans are not known, and the positions of Psi were determined on four tRNAs and U2 snRNA. The uridine at position 27 of tRNA(Val) (AAC), a putative Pus1p-modification site, was converted into Psi in the wild-type worms, but the tRNA(Val) (AAC) from mutant worms lacked the modification. Psi formation at positions 13, 32, 38 and 39, all of which should be modified by other pseudouridine synthases, was not affected by the loss of Pus1p. The absence of Pus1p in C. elegans had no effect on the modification of U2 snRNA in vivo, even though worm U2 snRNA has a Psi at position 45 (the equivalent of yeast U2 snRNA position 44) and at four other positions. This result was unexpected, given the known dual specificity of yeast Pus1p.
Pseudouridine modification in Caenorhabditis elegans spliceosomal snRNAs: unique modifications are found in regions involved in snRNA-snRNA interactions.
BMC molecular biology. 6:20. Abstract
BACKGROUND: Pseudouridine (Psi) is an abundant modified nucleoside in RNA and a number of studies have shown that the presence of Psi affects RNA structure and function. The positions of Psi in spliceosomal small nuclear RNAs (snRNAs) have been determined for a number of species but not for the snRNAs from Caenorhabditis elegans (C. elegans), a popular experimental model system of development. RESULTS: As a prelude to determining the function of or requirement for this modification in snRNAs, we have mapped the positions of Psi in U1, U2, U4, U5, and U6 snRNAs from worms using a specific primer extension method. As with other species, C. elegans U2 snRNA has the greatest number of Psi residues, with nine, located in the 5' half of the U2 snRNA. U5 snRNA has three Psis, in or near the loop of the large stem-loop that dominates the structure of this RNA. U6 and U1 snRNAs each have one Psi, and two Psi residues were found in U4 snRNA. CONCLUSION: The total number of Psis found in the snRNAs of C. elegans is significantly higher than the minimal amount found in yeasts but it is lower than that seen in sequenced vertebrate snRNAs. When the actual sites of modification on C. elegans snRNAs are compared with other sequenced snRNAs most of the positions correspond to modifications found in other species. However, two of the positions modified on C. elegans snRNAs are unique, one at position 28 on U2 snRNA and one at position 62 on U4 snRNA. Both of these modifications are in regions of these snRNAs that interact with U6 snRNA either in the spliceosome or in the U4/U6 small nuclear ribonucleoprotein particle (snRNP) and the presence of Psi may be involved in strengthening the intermolecular association of the snRNAs.
Blood lead concentrations in a remote Himalayan population.
Science (New York, NY). 210:1135-7. Abstract
The lead content in the air at the foothills of the Himalayas in Nepal was found to be negligible. The concentration of lead in the blood of 103 children and adults living in this region was found to average 3.4 micrograms per deciliter, a level substantially lower than that found in industrialized populations.