Cellular proliferation in the urorectal septation complex of the human embryo at Carnegie stages 13–18: a nuclear area‐based morphometric analysis

Abstract

In order to analyse the patterns of cellular proliferation both in the mesenchyme of the urorectal septum (URS) and in the adjacent territories (posterior urogenital mesenchyme, anterior intestinal mesenchyme and cloacal folds mesenchyme), as well as their contribution to the process of cloacal division, a computer-assisted method was used to obtain the nuclear area of 3874 mesenchymal cells from camera lucida drawings of nuclear contours of selected sections of human embryos [Carnegie stages (CSs) 13-18]. Based on changes in the size of the nucleus during the cellular cycle, we considered proliferating cells in each territory to be those with a nuclear area over the 75th percentile. The URS showed increasing cell proliferation, with proliferation patterns that coincided closely with cloacal folds mesenchyme, and with less overall proliferation than urogenital and intestinal mesenchymes. Furthermore, at CS 18, we observed the beginning of the rupture in the cloacal membrane; however, no fusion has been demonstrated either between the URS and the cloacal membrane or between the cloacal folds. The results suggest that cloacal division depends on a morphogenetic complex where the URS adjacent territories could determine septal displacement at the time that their mesenchymes could be partially incorporated within the proliferating URS.

The development of the cloaca in the human embryo

“…Cell replication rates in the cloacal wall and its surrounding mesenchyme appear similar in human (Nebot‐Cegarra et al. ) and mouse embryos (Matsumaru et al. ), but rapid proliferation may continue longer in mesenchyme than epithelium (Matsumaru et al.…”

“…Cell replication rates in the cloacal wall and its surrounding mesenchyme appear similar in human (Nebot-Cegarra et al 2005) and mouse embryos (Matsumaru et al 2015), but rapid proliferation may continue longer in mesenchyme than epithelium (Matsumaru et al 2015). Observed regional differences in growth, therefore, point to regional accumulation of extracellular matrix or regional differences in cell death.…”

“…The cloaca is usually shown as a midsagittal drawing, with histological sections to support developmental processes in other planes. In addition, the growth pattern in the cloacal region has been globally described (van der Putte, 2004), with most quantitative histological data addressing cell proliferation and apoptosis (Sasaki et al 2004;Nebot-Cegarra et al 2005;Matsumaru et al 2015;Huang et al 2016). To clarify the growth pattern and the fate of the components of the cloacal region, we reinvestigated the changes in shape of the cloaca, including its lumen, wall and surrounding mesenchyme in human embryos and fetuses between 4 and 10 weeks of development.…”

Perineal Groove-A Case Report

“…Studies also revealed an endodermal origin of the perineum, which is the first demonstration that endoderm differentiates into skin (4). Disturbances in spatial and sequential proliferation control and septal displacement of the urorectal septum by adjacent mesenchyme might be responsible for this type of mild malformation (5). Perineal groove might be associated with other regional anomalies like perineal ectopic anus or penoscrotal hypospadia (6).…”

Development of the caudal part of the human embryo

“…The cloaca is usually shown as a midsagittal drawing, with histological sections to support developmental processes in other planes. In addition, the growth pattern in the cloacal region has been globally described (van der Putte, 2004), with most quantitative histological data addressing cell proliferation and apoptosis (Sasaki et al, 2004, Nebot-Cegarra et al, 2005, Matsumaru et al, 2015, Huang et al, 2016. To clarify the growth pattern and the fate of the components of the cloacal region, we reinvestigated the changes in shape of the cloaca, including its lumen, wall, and surrounding mesenchyme in human embryos and foetuses between 4 and 10 weeks of development.…”