Defining new methods to assess the impacts of endocrine disrupting chemicals to reproductive development

© 2020 Luke Christopher GoversHypospadias is the most common persisting congenital abnormality in males, affecting one in 125 live male births in Australia and the U.S.A. Characterised by the abnormal placement of the urethra in the ventral surface of the penis, hypospadias is associated with a reduced fertility and other differences in sexual development (DSDs). Alarmingly, numerous countries have observed a 50% increase in the incidence of hypospadias over the last 50 years. The development of the penis is hormone dependent, and exposure to endocrine disrupting chemicals (EDCs) which alter the hormonal signalling in the male reproductive tract has been implicated in driving the increase in hypospadias. Despite its high incidence, significant gaps in our understanding of normal penis development and the aetiology of hypospadias are apparent. In this thesis I examine the hormonal control of normal penis development and the induction of hypospadias by EDCs. Since oestrogenic EDCs are among the most pervasive in our environment, I first examined the endogenous and exogenous role for oestrogen in the development of the penis and hypospadias. Using oestrogen signalling deficient mouse lines I demonstrate that endogenous oestrogen is required for normal penis development and that any disruption to oestrogen signalling results in mild hypospadias. Additionally, I developed a novel in vitro culturing method to isolate the embryonic penis and demonstrate that exogenous oestrogen and oestrogenic EDCs can directly impact the penis to cause hypospadias. This mechanism of action was previously undescribed and it was assumed that oestrogens impacted androgen output from the testis to cause hypospadias. Together these data are a significant shift in our understanding of the hormonal control of penis development and the mechanisms and range of EDCs which may induce hypospadias. Further exploiting my genital tubercle culture system I sought to define the molecular targets downstream of altered hormonal signalling in the penis. The findings from this work have helped to define some of the molecular drivers of hypospadias during early development and identified several critical signalling pathways which seem to be very sensitive to an altered hormonal environment. We have also been able to define genes which seem particularly sensitive to certain EDCs which can be used in future studies to develop high through-put assays to classify and assess potential EDCs. Together the data from this thesis have improved our understanding of penis development and how this process is disrupted in the presence of EDCs. This thesis has provided a valuable first step in describing new mechanisms through which EDCs can induce hypospadias which is vital to reform current policies and produce new guidelines on the usage of EDCs