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The control of growth and metabolism in Caenorhabditis elegans
Umeå University, Faculty of Medicine, Umeå Centre for Molecular Pathogenesis (UCMP) (Faculty of Medicine).
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The control of growth is a poorly understood aspect of animal development. This thesis focuses on body size regulation in Caenorhabditis elegans, and in particular, how worms grow to a certain size.

In C. elegans, a key regulator of size is the TGFβ homologue DBL-1. Mutations that deplete the worm of DBL-1 result in a small body size, whereas overexpression of the gene renders long animals. The small mutants have the same number of cells as wild type suggesting that some or all cells are smaller. DBL-1 activates a TGFβ receptor leading to the nuclear localization of three Smad proteins which then initiate a transcriptional program for size control whose targets are mainly unknown. In order to learn more about how body size in C. elegans is regulated, we set up EMS mutagenesis screens to identify new loci that caused a long phenotype. A subset of the genes we have identified might function in the TGFβ signaling pathway regulating growth while others likely function in parallel pathways.

One gene that we found in this screen, lon-3, encodes a cuticle collagen that genetically lies downstream of the DBL-1 TGFβ signaling pathway. Interestingly, loss of function mutations in lon-3 result in a Lon phenotype, whereas increasing the amount of LON-3 protein cause the worms to be dumpy, i.e. shorter, but slightly fatter than wild type. LON-3 is expressed in the hypodermis, the tissue from which the cuticle is synthesized and in which TGFβ signaling, regulating body size, has its focus. This study and previous work have shown that DBL-1 may affect body volume via effects on hypodermal nuclear ploidy, however this is unaffected in lon-3 mutants. Consistent with this finding, the volume of lon-3 mutant worms is not different from wild type. Taken together, our results suggest that another mechanism, by which TGFβ signaling can regulate body length, is by altering the shape of the cuticle via its effect on lon-3 and possibly other cuticle collagens.

Studies in worms, flies and mice show that body size and nutrient allocation are closely connected. p70 S6-kinase (S6K) is a known regulator of cell and body size that also plays a role in metabolism. In mice and flies S6K mutants are much smaller than wild type. Our work on the worm homolog, rsks-1, shows that in worms as well, this gene is important for growth regulation and cell size. However, this effect seems to be at least in part independent of DBL-1 TGFβ signaling. Furthermore, rsks-1mutants have a 50 % increase in the amount of stored fat. Fatty acid metabolism has been shown to play an important role in environmental adaptation, especially in regards to temperature changes. Consistent with this idea, rsks-1 mutants appear to have difficulties in adjusting to such changes, reflected in a much-decreased fecundity at 15 and 25 °C compared to their cultivation temperature (20 °C).

Within the nervous system the gene is specifically expressed in a subset of the chemosensory neurons that, when nutrients are abundant, secrete signals that promote growth. Intriguingly, this expression seems to be negatively regulated by insulin- like signaling, in contrast to the positive regulation of S6K by insulin in Drosophila and mice. Taken together we show that rsks-1 is an important regulator of growth and fat metabolism in Caenorhabditis elegans.

Place, publisher, year, edition, pages
Umeå: Umeå centrum för molekylär patogenes (UCMP) (Medicinska fakulteten) , 2006. , 45 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1010
Keyword [en]
TGFβ, insulin, collagen, p70 S6K, metabolism, growth, dauer
Keyword [la]
Caenorhabditis elegans
National Category
Biochemistry and Molecular Biology
Identifiers
URN: urn:nbn:se:umu:diva-710ISBN: 91-7264-034-0 (print)OAI: oai:DiVA.org:umu-710DiVA: diva2:144284
Public defence
2006-03-18, Major Groove, 6L, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2006-02-24 Created: 2006-02-24 Last updated: 2009-10-05Bibliographically approved
List of papers
1. Increased or decreased levels of Caenorhabditis elegans lon-3, a gene encoding a collagen, cause reciprocal changes in body length.
Open this publication in new window or tab >>Increased or decreased levels of Caenorhabditis elegans lon-3, a gene encoding a collagen, cause reciprocal changes in body length.
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2002 (English)In: Genetics, ISSN 0016-6731, E-ISSN 1943-2631, Vol. 161, no 1, 83-97 p.Article in journal (Refereed) Published
Keyword
Amino Acid Sequence, Animals, Caenorhabditis elegans/*genetics/growth & development, Caenorhabditis elegans Proteins/*genetics/physiology, Cloning; Molecular, Collagen/*genetics/physiology, Gene Dosage, Molecular Sequence Data, Neuropeptides/genetics, Transforming Growth Factor beta
Identifiers
urn:nbn:se:umu:diva-17952 (URN)12019225 (PubMedID)
Available from: 2007-11-23 Created: 2007-11-23 Last updated: 2017-12-14Bibliographically approved
2. Identification of new loci involved in the regulation of body size in C. elegans
Open this publication in new window or tab >>Identification of new loci involved in the regulation of body size in C. elegans
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Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-4963 (URN)
Funder
Available from: 2006-02-24 Created: 2006-02-24 Last updated: 2010-11-26Bibliographically approved
3. S. Caenorhabditis elegans RSKS-1, a homologue of p70 S6 kinase, functions in sensory neurons to modulate fat metabolism and entry into dauer.
Open this publication in new window or tab >>S. Caenorhabditis elegans RSKS-1, a homologue of p70 S6 kinase, functions in sensory neurons to modulate fat metabolism and entry into dauer.
Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:umu:diva-4964 (URN)
Available from: 2006-02-24 Created: 2006-02-24Bibliographically approved
4. A new technique for genetic mosaic analysis in the nematode Caenorhabditis elegans
Open this publication in new window or tab >>A new technique for genetic mosaic analysis in the nematode Caenorhabditis elegans
Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-4965 (URN)
Available from: 2006-02-24 Created: 2006-02-24 Last updated: 2010-01-13Bibliographically approved

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