Karen Clark and Kim Bekas Present in Genetics Student Seminar 6/12/17
CRISPR-Cas9 Gene Editing Yields a Novel Rat Model of the Metabolic Syndrome
Karen C Clark BS, Janette M Pettus BS, Justin L Grobe, PhD Anne E Kwitek, PhD
Department of Pharmacology, University of Iowa Carver College of Medicine; Interdisciplinary Graduate Program in Genetics, University of Iowa Carver College of Medicine
Metabolic Syndrome (MetS) is the clinical presentation of three or more risk factors—central obesity, dyslipidemia (elevated triglycerides, low HDL), hyperglycemia and hypertension—each of which contributes to increased risk of heart disease, diabetes and stroke in more than 20% of U.S. adults. There is strong evidence that MetS and its symptoms are highly heritable, yet identification of causative genes remains elusive, likely due to the complexity of the syndrome. Genome-wide association studies in human populations have fallen short in determining the causative loci; therefore, we employ the genetically tractable inbred Lyon Hypertensive rat model to tease apart the complex etiology of MetS.
Using a genome-wide approach, we previously identified a completely novel gene on rat chromosome 17 (RNO17) using a combination of QTL and eQTL mapping and gene network analysis, and found that RGD1562963 (RGD) has genetic effects on components of MetS.
CRISPR-Cas9 gene editing was used to introduce insertion and deletion mutations (indels) in exon 2 of RGD, and we are currently studying the mutations’ effects in male and female LH-derived rats. Though experiments are ongoing, preliminary data indicates homozygous RGD mutant females have increased resting aerobic metabolic rate (RMR) compared to wild-type controls—as measured by respirometry and core body temperature—and are hypertensive, especially when challenged with a high salt diet.
Our studies suggest RGD exerts pleiotropic effects on various components of MetS, and inhibition of this gene at the whole body level is tolerated. The continued study of this rat model of Metabolic Syndrome has the potential to functionally validate a completely uncharacterized regulatory gene, and provide novel targets for pharmacological intervention in the treatment of components of the Metabolic Syndrome.
Missing the Marx: Groucho function in Wnt Signaled Asymmetric Cell Division
Kimberly N. Bekas; Bryan T. Phillips
Genetics Graduate Program, University of Iowa, Iowa City, IAAsymmetric cellular divisions (ACDs) are a fundamental component of developmental processes that result in two daughter cells with differential cell fate at birth. C. elegans uses a modified version of the conserved Wnt/beta-catenin signaling pathway to regulate its many ACDs in embryonic and larval development. The DNA binding protein TCF/POP-1 functions in the Wnt/beta-catenin asymmetry pathway to differentially regulate gene expression in the daughter cells resulting from an ACD. The ability of POP-1, to repress or activate gene expression relies on interactions with Groucho family corepressors or the coactivator beta-catenin/SYS-1, respectively. The Groucho corepressors function in fate determination and are expressed in asymmetrically dividing tissues, such as the seam cells, yet a role for these corepressors in ACD has not been demonstrated. For this reason, we investigated the function of Groucho in the seam cell lineage, which divides asymmetrically to produce a pluripotent seam cell and terminally differentiated hypodermal cell. Seam cell fate appears to heavily rely on repression rather than activation since knockdown of the POP-1 increases seam cell number while knockdown SYS-1 does not affect seam cell number. If Groucho were required for POP-1 repression in the unsignaled daughter after ACD, we expect to see duplication of the signaled fate following Groucho depletion, similar to the POP-1 RNAi phenotype. Surprisingly, no defects in seam cell fates following corepressor depletion were seen. However, we sensitized cells via POP-1 RNAi and determined that, at low levels of POP-1 knockdown, additional knockdown of Groucho results in an increase in seam cell number that resembles the full POP-1 knockdown phenotype. This enhancement provides evidence that Groucho functions in terminal differentiation of the dividing seam cells to confer hypodermal cell fate. Current efforts include testing the role of POP-1 domains that interact with SYS-1 and DNA, using specific pop-1 alleles in combination with Groucho loss-of-function. Preliminary evaluation of a transgenic strain encoding a POP-1 deficient in SYS-1 binding, pop-1(q645) coupled with a sys-1 hypomorph (q544), shows no significant defects in seam cell ACD. These data indicate that differential transcriptional repression between the two daughters provided by Grouchos, rather than activation SYS-1, may be the critical effect of Wnt signaling in the unsignaled daughter.