Independent original article The migrating gubernaculum grows like a limb bud Sophie S. Nightingale a,b , Patrick Western c,d , John M. Hutson a,b,c, ⁎ a Department of General Surgery, Royal Children's Hospital, Melbourne 3052, Australia b Murdoch Children's Research Institute, Melbourne 3052, Australia c Department of Paediatrics, University of Melbourne, Melbourne 3052, Australia d Australian Research Council Centre of Excellence in Biotechnology and Development, Murdoch Children's Research Institute, Melbourne 3052, Australia Received 6 August 2007; accepted 8 August 2007 Index words: Testicular descent; Cryptorchidism; Undescended testes; Gubernaculum; Limb bud; Fgf10; Hoxa10 Abstract Background: The gubernaculum is crucial for testicular descent, and in the second, or inguinoscrotal, phase of descent it has no caudal attachments. Cranially, it is attached to the testis, but its caudal free tip migrates to the scrotum controlled by the genitofemoral nerve. Recent studies show active proliferation in the tip. We hypothesized that the gubernacular tip may grow like a limb bud. Methods: We performed whole-mount in situ hybridization studies on male and female fetal mice (ages, E14.5-E18.5; n = 162) looking for limb bud regulatory factors. Results: Our results showed that a member of the fibroblast growth factor (Fgf) family, Fgf10, and Hoxa10 were both expressed in the male gubernaculum at E14.5, and Hoxa10 was also expressed in the E16.5 mice. Weak staining was seen in the female gubernaculum for Hoxa10 on days E14.5 and E16.5, whereas no staining for Fgf10 was seen in the female gubernaculums. Conclusions: These studies, although preliminary, suggest limb bud regulators are essential for gubernacular growth. Hox genes and Fgfs may be fruitful areas of research to unravel the molecular control of gubernacular migration during testicular descent. © 2008 Published by Elsevier Inc. Testicular descent is a complex process generally accepted to occur in 2 phases: the transabdominal phase followed by the inguinoscrotal phase [1]. Common to both these phases is the gubernaculum, which plays a role throughout the entire process. The gubernaculum has often been described as “jelly-like.” and this has implied a passive nature to the organ. Over the last few decades, studies have shown that the gubernaculum undergoes many significant changes during testicular descent, suggesting that the gubernaculum is a more complex structure than previously thought. The two phases of testicular descent are mediated by different hormones: insulin-like hormone 3 (INSL 3) mediates the transabdominal phase, and androgens are involved in the second phase. The gubernaculum is affected by both hormones but they appear to act directly (INSL 3) and indirectly (androgens), which also implies that the gubernaculum is developmentally and functionally complex. The vertebrate limb forms in a specific region of the developing embryo according to a set of preprogrammed signals. The limb bud has been extensively studied and has become a model for studying many other organ systems [2-5]. It is well established that there are distinct regions within the limb bud that produce differing signals and act in Presented at the Pacific Association of Pediatric Surgeons meeting, Queenstown, New Zealand, April 15-19, 2007. ⁎ Corresponding author. Department of General Surgery, Royal Children's Hospital, Parkville, Victoria 3052, Australia. Tel.: +61 3 9345 5805; fax: +61 3 9345 7997. E-mail address: john.hutson@rch.org.au (J.M. Hutson). www.elsevier.com/locate/jpedsurg 0022-3468/$ – see front matter © 2008 Published by Elsevier Inc. doi:10.1016/j.jpedsurg.2007.08.016 Journal of Pediatric Surgery (2008) 43, 387–390