“Four Core Genotypes” Rats: Comparing Xx and Xy Rats with the Same Type of Gonads to Detect Sex Chromosome Effects That Cause Sex Differences in Physiology and Disease
Arthur P. Arnold1, Xuqi Chen1, Michael Gryzbowski2, Lynn Lazcares2, Akiko Takizawa2, Laurent Vergnes3, Helen Skaletsky4, David C Page4, Karen Reue3, Melinda R. Dwinell2, and Aron M. Geurts2
1Department of Integrative Biology & Physiology, University of California, Los Angeles, California; 2Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin; 3Department of Human Genetics, David Geffen School of Medicine, University of California, Los Angeles; 4Howard Hughes Medical Institute, Whitehead Institute, Cambridge, Massachusetts
The mouse Four Core Genotypes (FCG) model has successfully allowed comparison of XX and XY mice with the same type of gonads, to determine if sex differences in mouse traits are caused by cell-autonomous effects of X and Y genes (“sex chromosome effects”, SCEs). For example, among 30 brain regions shown by MRI to have different volumes in FCG mice, almost 45% showed differences caused SCEs (XX vs. XY), whereas others showed differences caused by gonadal hormones. We sought to produce an FCG-like model in rats, because many sex differences are studied in rat brain and behavior (and other traits), but measuring SCEs has not been possible in rats. A major issue is that rats have 10 or more Sry genes, with unknown functions beyond testis determination. We knocked out the testis-determining function on the Y chromosome using CRISPR, to produce XYΔ gonadal female rats that breed easily, producing and XYΔ and XX rats, both with functional ovaries, in the same litters. These rats are compared to measure the differential effects of XX vs. XY sex chromosomes (SCEs) in rats with ovaries. Secondly, we integrated a BAC transgene (Sry-tg) encoding Sry4A, Sry3C, and Sry1, onto an autosome to cause testis development in XX rats lacking any other Y genes, showing for the first time that these 3 Sry genes are sufficient as a group to cause testis differentiation. XY(Sry-tg+) males, mated to WT XX females, produce XX(Sry-tg+) and XY(Sry-tg+) rats with testes, allowing comparison of XX and XY rats with testes. XX(Sry-tg+) rats have testes lacking sperm, as expected from studies in other mammals. XX and XY rats have similar anogenital distance in the first postnatal week if they have the same type of gonad, suggesting XX and XY levels of testosterone prenatally are comparable within each gonadal sex. Body weight at 7 weeks was higher in rats with testes than ovaries, as previously reported, but there was also greater body weight in XY than XX rats, an SCE. XX and XY rats differed in fat storage in gonadal fat pads, but fat accumulation in subcutaneous fat pads was different in rats with ovaries vs. testes. Thus, we have created a novel rat model that allows easy breeding of XX and XY rats with the same type of gonads, which can be used to investigate SCEs that cause sex differences in any rat phenotype.
Supported by NIH grants OD026560 to APA, MRD, AMG, HL114474 to MRD and AMG, DK120342 to KR.
Breakout Room: Arnold, Art
View Poster: https://uclacns.org/symposium2021/1-Arnold-Art.pdf