In mammals, the transcription factor SRY, encoded by the Y chromosome, is normally responsible for triggering the indifferent gonads to develop as testes rather than ovaries. However, testis differentiation can occur in its absence. Here we demonstrate in the mouse that a single factor, the forkhead transcriptional regulator FOXL2, is required to prevent transdifferentiation of an adult ovary to a testis. Inducible deletion of Foxl2 in adult ovarian follicles leads to immediate upregulation of testis-specific genes including the critical SRY target gene Sox9. Concordantly, reprogramming of granulosa and theca cell lineages into Sertoli-like and Leydig-like cell lineages occurs with testosterone levels comparable to those of normal XY male littermates. Our results show that maintenance of the ovarian phenotype is an active process throughout life. They might also have important medical implications for the understanding and treatment of some disorders of sexual development in children and premature menopause in womenIt also gives hope to Trans men that they may be able to father children one day. We're still at a very early stage yet, what works on mice my not work on men, and the testes may require other factors to become functional, but there's real hope. Hope that the guys will be able to change their ovaries into functional testes.
There's still the problem of the, um, er, delivery system to be sorted out. That will require additional work, probably with stem cells building erectile tissue. But one of those isn't necessary to become a father - I know, from personal experience.
This research may possibly open up a whole new field. The ability to correct sex when the neurology is anomalous. Possibly for women too.
I have a dream... that possibly within my lifetime, a girl born trans will be able to give birth, as her instincts and neurology scream that she should. As mine does too, even now. Not this incarnation though. Besides, I have a son, and the exact process isn't important, it's the result.
Trans women may in many cases exhibit almost stereotyped female thought patterns, far more so than the standard factory model female. I think that that's because they have to be more strongly gendered than average to even attempt transition, or it may be an artifact of the high hormone levels some require. Or both.