How the penis arises

Development of male reproductive organs does not depend only on testosterone

How does the penis develop in a male embryo? © Janulla / thinkstock
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Looking at the development of the penis: Not only is testosterone crucial for a healthy development of the male member - a second hormone plays an equally important role. As researchers have found, this process in the embryo is also controlled by the hormone androsterone. Unlike testosterone, the messenger substance is not secreted by the fetal testicles but by the placenta. This could explain why problems with the mother cake often lead to malformations of the male genitalia.

The external sexual organs of men and women develop from the same plant: the so-called genital hump. In the course of embryonic development, this curvature between the legs of a girl gradually matures towards the clitoris. In the case of a male embryo, on the other hand, the penis develops from this.

For the male member to develop, the testes of the fetus must release the steroid hormone testosterone. This messenger substance is converted by enzymes in the genital hump into its biologically particularly active form dihydrotestosterone, in short DHT. But this process is not the only one that is crucial for normal penile development.

A second signal path

Moreover, as researchers have recently discovered, penile development seems to depend on a second signaling pathway. This "backdoor" path also leads to the production of DHT in the genital hump - however, further details were unclear so far. To change this, Peter O'Shaughnessy of the University of Glasgow and his colleagues have now gone in search of the womb in the womb.

For their study, the researchers studied the concentration of steroid hormones in the plasma and tissue of human fetuses in the second trimester of pregnancy - a period in which major steps in penile development take place. The analysis by mass spectrometry showed that especially the concentration of a hormone was conspicuously high: that of the androgens androsterone. display

Key hormone Androsterone

This messenger substance accumulated in the plasma of male fetuses. In females, however, his concentration was significantly lower. "Our findings reveal that androsterone is the main androgen of the backdoor path, " the team writes. But where is this hormone synthesized?

Further investigations showed: it is not the testicles that produce this second DHT precursor. Genetic analysis indicated that the synthesis of androsterone occurs mainly in the liver of the fetus and in the placenta. The researchers assume that the hormone in the cake is derived from the messenger substance progesterone which is released there in large quantities.

The role of the placenta

It is now clear that masculinization of the male embryo is mediated by circulating testosterone, but also by androsterone. "This process does not just depend on the testes, but also on other tissues - especially the placenta, " says O'Shaughnessy's colleague Michelle Bellingham.

According to the researchers, this fact may now also explain why problems with the placenta often lead to disturbances in male genital development - for example the so-called hypospadias, a malformation of the urethra. "The external male genitalia are the most frequent site of congenital malformations in humans. Up to 0.8 percent of male births are affected, "concludes the team. (PLOS Biology, 2019; doi: 10.1371 / journal.pbio.3000002)

Source: PLOS

- Daniel Albat