Breast cancer and prostate cancer. According to the classical view steroid hormone actions are thought to be regulated by systemic hormone levels, where endocrine glands produce the hormones and blood circulation delivers the hormones to target organs. However, accumulative evidence has shown that the control of steroid hormone actions is also regulated at the level of target cell metabolism. 

Due to the crucial roles of steroid hormones in physiological functions and in the etiology of several diseases, a better understanding of steroid hormone metabolism is needed. 

In this study, we generated a conventional global knockout mouse model, hydroxysteroid 
(17β) dehydrogenase 1 (hsd17b1ko), to achieve a better understanding of enzymatic regulation of steroid hormone actions and of the role of the hsd17b1 in the development of reproductive organs and fertility in females and males. This study revealed that a lack of the enzyme does not have an impact on fetal or pubertal development in either males or females. However, steroid synthesis is affected in both females and males, and enzyme deficiency leads to severely impaired fertility in females and infertility in males. Thus, this study indicates that the hsd17b1 enzyme plays a critical role in regulating steroid hormone synthesis and actions, and that a lack of the enzyme has a profound influence on mouse gonadal function in both males and females. 

In summary, the produced knockout mouse model provides a tool and knowledge to understand steroid hormone synthesis and actions in reproductive tissues.