Defining the role of Sf1 in urethral closure

Hypospadias is one of the most common birth defects in the world affecting nearly 1% of newborn boys.
Hypospadias is the result of disrupted urethral closure where the urethra exits ventrally along the shaft of the
penis. The etiology of 70% of urethral closure defects remains unexplained. Androgen signaling in the penis
drives cell-to-cell communication between the urethra and the adjacent mesenchyme, which then influences
closure of the urethra. Normal penis development requires testosterone. In the absence of testosterone
produced by the testis, the urethra fails to close, leading to severe hypospadias. The testis-derived
testosterone eventually reaches the presumptive penis, and is metabolized into the more potent
dihydrotestosterone by 5-α reductase. Dihydrotestosterone then binds androgen receptor that are localized
within the penis, which transcribes a suite of genes that induce penis development. Surprisingly the regulation
of 5-α reductase and the diversity of cell populations involved in urethral closure are not well understood.
Recently, I discovered a unique cell population in the penis that expresses the steroidogenic enzyme master
regulator, Steroidogenic Factor 1 (Sf1). These cells are localized in the ventral-proximal aspect of the penis,
express both androgen receptor and 5-α reductase, and appear to be required for urethral closure. My central
hypothesis is that these SF1+ cells contribute to proper urethral closure by both producing and responding to
androgens. In the two phases of my K99/R00, I will investigate the role of SF1+ cells in penis development and
urethral closure. In the K99 phase, I will define the role of SF1+ cells and Sf1 the gene in urethral closure. I will
use a combination of the Diptheria toxin, cell ablation mouse model and a penis specific Sf1 gene knockout
mouse model. I hypothesize that these cells are essential for urethral closure and are responsible for the
penises steroidogenic capacity to convert testosterone to dihydrotestosterone. In the R00 phase, I will reveal
how androgen signaling influences SF1+ cell differentiation and urethral closure. Using SF1+ cell conditional
androgen receptor knockouts and chromatin binding assays, I will test the hypothesis that androgens are
directly involved in SF1+ cell function and differentiation. The results from this study will establish the role of a
novel cell population, the function of the gene, Sf1, and androgen responsiveness in penis urethral closure.
This new knowledge will provide a better understanding of the mechanisms involved in the occurrence of
hypospadias and will further human investigations on the etiology of hypospadias. Ultimately if there is a more
comprehensive understanding of penis development, we can begin to develop strategies to prevent this defect
that impacts millions of boys. With the technical skills I already have, the data generated in this proposal, and
the skills I will acquire during the fellowship, I will be well-poised to become an independent Principal
Investigator at an academic institution. Once at my future job, I will be fully equipped to submit an independent
R01 grant to further study the androgen responsiveness of SF1+ cell in the penis.

Grant Number: 5R00DK132460-04
NIH Institute/Center: NIH
Principal Investigator: Ciro Amato