Mathematical modelling of gubernaculum during inguino-scrotal migration shows limb bud characteristics

The gubernaculum is postulated to grow like an embryonic limb bud during inguinoscrotal descent in rodents. Recently, modelling of limb bud growth suggests the undifferentiated, distal "progress zone" provides molecular morphogenic signals, rather than cell division, as previously thought. We aimed to develop a mathematical gubernacular growth model, hypothesising that it would mimic limb buds through evolutionary conservation.

Histology was done on Sprague-Dawley rats (day 2, 8; n=7/group) to determine gubernacular length, width, cell density in distal growth centre, middle and proximal cremaster muscle. Analysis of measurements enabled gubernacular growth modelling under variable growth centre sizes/densities, assuming no apoptosis.

Modelling found that gubernacular growth occurred mostly within cremaster muscle, rather than primarily in the undifferentiated mesenchymal tip, despite its higher mitotic rate. The growth centre accounted for ≤ 10% of total gubernacular enlargement/elongation.

These results suggest the gubernaculum elongates by proliferation throughout cremaster muscle like a limb bud. The distal undifferentiated tip may provide signalling molecules for growth, which could be a fruitful source for causes of failed migration/elongation in cryptorchidism.