The regulation of carnitine palmitoyltransferase 1 (CPT1) mRNA splicing by nutrient availability in Drosophila fat tissue
Open Access
- Author:
- Truong, Huy
- Area of Honors:
- Biology
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Justin Di Angelo, Thesis Supervisor
Sandy Feinstein, Thesis Honors Advisor - Keywords:
- CPT1
splicing
mRNA
9G8
obesity
lipid
PKA
SR protein
starvation
isoforms
exon
triglyceride - Abstract:
- After a meal, excess nutrients are stored within adipose tissue as triglycerides in lipid droplets. Previous genome-wide RNAi screens in Drosophila cells have identified mRNA splicing factors, genes that function in the expression and processing of mRNAs, as being important for lipid droplet formation. The DiAngelo lab has previously shown that a class of mRNA splicing factors called serine/arginine-rich (SR) proteins, which help to identify intron/exon borders, are important for triglyceride storage in Drosophila fat tissue, partially by regulating the splicing of the gene for carnitine palmitoyltransferase 1 (CPT1), an enzyme important for mitochondrial ß-oxidation of fatty acids. The CPT1 gene in Drosophila generates two major isoforms, with transcripts that include exon 6A producing more active enzymes than ones made from transcripts containing exon 6B. To investigate whether nutrient availability regulates CPT1 splicing in fly fat tissue, CPT1 transcripts were measured under fed and fasted/starved conditions. During ad libitum feeding, control flies produce more CPT1 transcripts containing exon 6B while fasting for 24 hours results in a shift in CPT1 splicing to generate more transcripts containing exon 6A. Enzymes made from transcripts with exon 6A are more active, consistent with the need for triglyceride breakdown to generate energy under starvation. The SR protein 9G8 is necessary for regulating nutrient-responsive CPT1 splicing as decreasing 9G8 levels in fly fat tissue blocks the accumulation of CPT1 transcripts including exon 6A during starvation. The role of protein kinase A (PKA), a mediator of starvation-induced lipid breakdown, in regulating CPT1 splicing during starvation was also investigated. In control flies, starvation resulted in more transcripts including exon 6A, but transcripts including exon 6A did not accumulate when PKA was inhibited during starvation, suggesting that PKA responds to starvation to control CPT1 splicing in fly fat tissue. Together, these results indicate that CPT1 splicing in adipose tissue responds to changes in nutrient availability contributing to the overall control of lipid homeostasis.