PgmNr D100: Mediator subunit skuld is required sex specifically for ovary development.

Authors:
H. Sultana; H. Yang; B. Oliver


Institutes
NIDDK, National Institutes of Health, Bethesda, MD.


Keyword: sex-specific traits and molecules

Abstract:

Organogenesis requires spatio-temporal regulation of gene expression. We use development of the female gonads as a model to understand gene expression regulation. In Drosophila melanogaster, female gonads consist of a pair of ovaries, which contain both germ cells and somatic cells. Somatic cells are indispensible for proper growth, differentiation, and sex determination of germ cells. Here we took two independent approaches to identify the genes that potentially affect germ cells nonautonomously. In the first approach, we performed a reverse genetic screen using the UAS-Gal4 system to knockdown genes in Traffic Jam positive somatic cells and screen for female sterility. We tested 1,119 genes in this screen and found 169 to be female sterile. In the second approach, we performed transcriptional profiling of the anterior ovariole consisting of germaria and round previtellogenic egg chambers, which are regions with close contact between germ cells and somatic cells. We performed RNA-Seq on 12 biological replicates of anterior ovariole and compared it to whole ovary. We found expression of 3,999 genes enriched in anterior ovariole compared to whole ovary (Padj<= 0.05). Out of these 73 were female sterile in the genetic screen. We selected 67 genes for further characterization that were either female sterile in the genetic screen or were enriched in the anterior ovariole RNA-Seq experiment. Development of both testes and ovaries was affected in the knockdown of 18 genes, whereas knockdown of three genes skuld, broad and misshapen gave ovary specific phenotypes. skuld (skd) is a component of the kinase domain of the mediator complex along with kohtalo (kto), Cyclin C and Cdk8. skd knockdown in somatic cells of the gonad resulted in developmental arrest of the ovaries but not the testes. In L3 larval ovaries, germ cells were not present in a zone like control ovaries but were spread across the ovary suggesting a nonautonomous role of skd in germ cell organization. skd and kto have been shown to function in a similar context in several tissues. When we knocked down kto we found an effect on the development of both testes and ovaries. Both at L3 and adult stages, mutant ovaries for skd and kto looked similar. However, kto mutant testes were thin and sterile at 29°C unlike skd mutant testes, which were fertile. We cross-validated this phenotype by investigating gene expression of skd and kto in ovaries vs. testes from different publically available RNA-Seq datasets. We found significant enrichment of skd expression (Padj<0.0001) in the ovaries compared to the testes whereas kto is expressed at comparable levels in both male and female gonads. Our study suggests differences in function of mediator components skd and kto in gonad development and also proposes a sex specific role of skd in ovary development.



Flybase Genetic Index:
1. FlyBase gene symbol: skd; FBgn: FBgn0003415
2. FlyBase gene symbol: kto; FBgn: FBgn0001324