UCLA

The sexually dimorphic nucleus of the preoptic area (SDN-POA) is one of the largest known sexual dimorphisms in the brain, and its discovery led to a greater understanding of sexual differentiation in non-gonadal tissues. The SDN-POA is larger in males, mostly due to gonadal hormones’ organizational effect around birth. The Four Core Genotypes (FCG) model in mice is an important model in understanding sex differences and is often used with other mouse models of disease and physiology. The FCG-like model in rats, better described as the Sry-modified rat model, is currently being developed in our lab. When established gonadal hormone effects are replicated in the Sry-modified rats, then people gain confidence in this newly developed model for sex differences. There are two components of the Sry-modified rat model. The first is the CRISPR-mediated reduction in dose of the testis-determining gene Sry on the Y chromosome (denoted as Y∆), producing XY∆ and XXY∆ rats with ovaries. The second component is the insertion of an Sry transgene onto an autosome (denoted as SryTG+), producing XX(SryTG+) rats with testes. These two separate modifications are bred in two breeding paradigms: transgenic and KO. The transgenic litters are produced by mating an XX female and an XY(SryTG+) male, and the KO litters are produced by mating an XY male and an XY∆ female. From these two breeding schemes, six genotypes are produced: XX gonadal females, XXY∆ gonadal females, XY gonadal males, XYY∆ gonadal males, XY(SryTG+) gonadal males, XX(SryTG+) gonadal males. Furthermore, mating XXY∆ gonadal females and XY(SryTG+) gonadal males produces two more viable genotypes: XXY∆(SryTG+) gonadal males and XYY∆(SryTG+) gonadal males. In total in the Sry-modified rats, there are eight genotypes produced and utilized for comparison. The SDN-POA can be examined in these eight genotypes and compared across groups of different sex chromosomes, gonads, and Sry and Y chromosome doses. The SDN-POA size is quantified through immunohistochemical staining for calbindin immunoreactive cells, but there are many variables that influence the quality of the immunohistochemistry. These variables include but are not limited to perfusion rates during preparation of the tissues, types of reagents used during the immunohistochemistry, and the concentrations of reagents. The SDN-POA is used for comparison because the development of this nucleus is heavily influenced by organizational effects of hormones, so it serves as a bioassay for testicular hormones before and around the time of birth. Furthermore, by measuring the sex differences in the SDN-POA in the Sry-modified rat model, it can help validate the model so that it can be used in other models of disease and physiology.