Chew, KY., Pask AJ., Hickford, D., Shaw, G., Renfree, MB., ‘A Dual Role for SHH during Phallus Development in a Marsupial’, Sexual Development, 2014; 8: 166-177.
An experiment by the ARC Centre of Excellence in Kangaroo Genomics and Department of Zoology, The University of Melbourne.
It is considered a fact that development of the sexual organ in male mammals is triggered by the sexual hormone androgen, yet little is known about the role of other factors in this development. Researchers designed an experiment to explore the role of factors such as genes, hormones, and in particular, SHH, which is known to ‘pattern’ the phallus. Tammar wallabies were chosen because both the male and female phalluses(1) of these animals develop following their birth and thus can be more easily examined than other mammals. The researchers state that they are “ideal models” because “developing young is [are] readily accessible for experimental manipulation”.
Thirty one ‘pouch age’ tammar wallabies were used in this experiment*. Of the thirty-one, five female wallabies were given an injection of androgen twenty-four days after birth with a twenty-six gauge needle; another four were given this injection at day twenty-nine. Of the twenty two male wallabies, six were castrated twenty-three days after birth, and eight were castrated at the twenty-ninth day. The remaining eight males were kept as a control group.
Finally, all thirty one animals were killed on the fiftieth day and dissected for further examination.
*Tammar foetal tissue and foetal phalluses were also used in this experiment. The only allusion to the welfare of the animals from which these samples were taken is the statement that their collection conformed to the Australian National Health and Medical Research Council guidelines and were approved by the University of Melbourne’s animal experimentation and ethics committee. In addition, several animal products were used to treat these foetal samples: goat serum; bovine serum; and IgG from rabbits.
The results of the study, the authors argue, suggest that SHH serves two roles: initially it patterns the genitals of both males and females. Later, following the increase of androgen in male wallabies, it directs the development of the male phallus.
Given that it was already known that androgen and SHH both served in the growth the male/female genitals, has the result of this study really advanced our scientific knowledge?
This experiment was supported by grants from the National Health and Medical Research Council of Australia.
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- (1) In this text the genital region (which at birth is identical) is referred to as phallus for both sexes, e.g. “can masculinize the female phallus”; “phallus size between males and females” (p168).