Regulation of glycogen phosphorylase genes in Dictyostelium discoideum

The cellular slime mold, Dictyostelium discoideum, provides an ideal model system to study eukaryotic development, cell differentiation, and aging. A crucial developmental event in Dictyostelium is glycogen degradation. The degradation of glycogen provides glucose monomers that are used to synthesize structural components necessary for cellular differentiation. Glycogen degradation is catalyzed by glycogen phosphorylase, and two developmentally regulated glycogen phosphorylase activities have been discovered in Dictyostelium. Glycogen phosphorylase 1 (gp-1) activity is predominant early in development, and is dependent upon 5’ AMP as a positive allosteric modifier; glycogen phosphorylase 2 (gp-2) activity peaks late in development and is independent of 5° AMP. I showed that these two glycogen phosphorylase activities are associated with unique proteins that are the products of two distinct, but related, genes. Both genes were observed to be typical Dictyostelium genes in a number of respects. The gp-1 and gp-2 enzymes were also found to be similar to glycogen phosphorylases from other organisms. I also examined the developmental expression of these genes and found that both mRNAs are developmentally regulated; gp-1 mRNA levels fluctuate during development, while gp-2 mRNA levels increase late in development. The expression of the gp-1 and gp-2 genes is regulated by exogenous cAMP. Exogenous cAMP enhances the level of gp-1 mRNA, apparently through a mechanism that requires intracellular cAMP signaling. Specific DNA sequence elements appear to be required for maximal vegetative and late developmental expression of gp-1. Exogenous cAMP induces the appearance of gp-2 mRNA via a mechanism that appears to be independent of intracellular cAMP signaling. Repeated TA-rich sequences located between nucleotides 193 and 305 upstream of the transcriptional start site are necessary for maximal cAMP induction of gp-2. I also examined the cell type specific expression of gp-1 and gp-2. gp-1 is expressed predominantly in pre-stalk cells. gp-2 1s expressed in both cell types in a temporally regulated fashion; this type of expression has not been reported for other Dictyostelium genes, but, given the importance of glycogen degradation in both stalk and spore cells, it is not inconceivable that such regulation 1s necessary.

Name thesis:degree_name

Ph. D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Biology

Department dc:contributor.department

Biology

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

1992

Author dc:creator

• Sucic, Joseph F.

Chair dc:contributor.committeechair

• Rutherford, Charles L.

Committee members dc:contributor.committeemember

• Falkinham, Joseph O. III
• Gregory, Eugene "Mick"
• Johnson, John L.
• Rogers, Patricia V.

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Dc Identifier Other

etd-06062008-170101

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/38380