Kidney Week

Abstract: FR-OR043

Reciprocal Antagonism between Ppargc1a and Sim1a Regulates Boundary Formation of the Proximal Straight Segment during Vertebrate Pronephros Development

Session Information

• Defining Cellular Composition and Mechanisms of Kidney Formation
  October 26, 2018 | Location: 4, San Diego Convention Center
  Abstract Time: 05:30 PM - 05:42 PM

Category: Development, Stem Cells, and Regenerative Medicine

• 501 Development, Stem Cells, and Regenerative Medicine: Basic

Authors

• Chambers, Joseph M., University of Notre Dame, Notre Dame, Indiana, United States

Joseph M. Chambers, PhD

• Wingert, Rebecca A., University of Notre Dame, Notre Dame, Indiana, United States

Rebecca A. Wingert,

Background

The genetic and molecular mechanisms that regulate boundary formation between adjacent segment populations are not fully understood. The pronephros of several vertebrates provides a simplified, tractable model to investigate fundamental mechanisms of segmentation, as this primitive kidney is comprised of proximal and distal segments that are conserved with mammalian nephrons, including humans.

Methods

Through a bioactive small molecule chemical genetic screen, we discovered that peroxisome proliferator-activated receptor (PPAR) signaling is essential for pronephros segmentation. Next, we found that the co-activator, ppargc1a, which binds activated PPARs to regulate transcription of target genes, is dynamically expressed in renal progenitors and is requisite for segmentation.

Results

ppargc1a^sa13186-/- mutants with a T->A substitution that results in a putative null allele have an reduced distal tubule segment and increased proximal tubule domain, which was recapitulated in subsequent knockdown studies and rescued with ppargc1a overexpression. Further, ppargc1a acts to promote tbx2b, a transcription factor necessary for proper formation of the distal segment. Interestingly, ppargc1a^sa13186-/- have an expanded sim1a domain, a transcription factor which is thought to regulate proximal segments. Conversely, ppargc1a expression was expanded in sim1a deficient embryos. This data suggests a negative regulation between the two factors. To test this interaction, we examined the proximal straight tubule domain in sim1a deficient, ppargc1a deficient, and doubly deficient embryos. While the loss of sim1a resulted in an abrogated proximal straight tubule, loss of ppargc1a resulted in expanded proximal straight tubule, but loss of both factors results in a completely restored segment boundary.

Conclusion

Taken together, this data strongly suggests that Ppargc1a and Sim1a act to counterbalance each other in an antagonistic fashion that is necessary for proper nephron segment boundary formation. These findings reveal for the first time how a layer of redundancy within the mechanism of segment boundary delineation is used to mitigate segment formation. Thus, these studies have discovered a useful paradigm to advance our understanding of nephron segmentation mechanisms.

Funding

• NIDDK Support