Cell membrane and mitotic markers show that the neonatal rat gubernaculum grows in a similar way to an embryonic limb bud

The migrating gubernaculum grows like a “limb bud”

“…More importantly, the finding of a putative "progress zone" in the gubernacular tip supports the notion that elongation of the gubernaculum to the scrotum may be similar to limb bud elongation [11]. Positive expression of both Fgf10 and Hoxa10 in the bulging gubernacular tip before the elongation phase suggests that the proximodistal regulators controlling limb bud growth are also activated before gubernacular growth, which commences around birth in mice.…”

Development of the Gubernaculum During Testicular Descent in the Rat

“…Is the cremaster muscle derived from the abdominal wall muscles, transversus abdominis and/or internal oblique, or does it develop separately within the gubernaculum? Recent studies from our own laboratory suggest that the gubernaculum develops a growth center that is similar to a progress zone within an embryonic limb bud (Na et al, 2007), but the origin of this putative growth center is unknown.…”

Growth of the rat gubernaculum in vitro and localisation of its growth centre

“…In addition, Lam et al [7] showed that the rat gubernaculum also undergoes an extensive elongation and migration to reach the scrotum and that simple eversion is insufficient to explain the distance it must travel. Harnaen et al [17] have also shown that the cremaster muscle grows from the distal end of the gubernaculum, presumably from the distal progress zone, and not from the proximal internal oblique muscle, as stated in most anatomy books [16,17]. All these studies support the view that the gubernaculum grows out of the inguinal abdominal wall by a process very similar to a developing limb bud rather than simply pulling or pushing the testis into the scrotum.…”

“…A number of recent studies from our laboratory have suggested that the active growth centre of the gubernaculum is in the tip, as shown by it being the site of maximal mitosis in vivo [15], as well as the site of active uptake of fluorescent cell wall markers in vitro [16,17]. Also, it is the site of the most active apoptosis in vitro in the absence of CGRP in the medium [18] (Chan et al, in press, 2009).…”

“…These results lead us to postulate that the rat gubernaculum may grow out of the abdominal wall in a manner analogous to an embryonic limb bud, which contains a distal region of undifferentiated fibroblasts that multiply to produce all the structures in the fully grown limb. This region is known as the "progress zone" [16,17].…”