R-Spondin 1/Dickkopf-1/Beta-Catenin Machinery Is Involved in Testicular Embryonic Angiogenesis

Abstract

Testicular vasculogenesis is one of the key processes regulating male gonad morphogenesis. The knowledge of the molecular cues underlining this phenomenon is one of today’s most challenging issues and could represent a major contribution toward a better understanding of the onset of testicular morphogenetic disorders. R-spondin 1 has been clearly established as a candidate for mammalian ovary determination. Conversely, very little information is available on the expression and role of R-spondin 1 during testicular morphogenesis. This study aims to clarify the distribution pattern of R-spondin 1 and other partners of its machinery during the entire period of testicular morphogenesis and to indicate the role of this system in testicular development. Our whole mount immunofluorescence results clearly demonstrate that R-spondin 1 is always detectable in the testicular coelomic partition, where testicular vasculature is organized, while Dickkopf-1 is never detectable in this area. Moreover, organ culture experiments of embryonic male UGRs demonstrated that Dickkopf-1 acted as an inhibitor of testis vasculature formation. Consistent with this observation, real-time PCR analyses demonstrated that DKK1 is able to slightly but significantly decrease the expression level of the endothelial marker Pecam1. The latter experiments allowed us to observe that DKK1 administration also perturbs the expression level of the Pdgf-b chain, which is consistent with some authors’ observations relating this factor with prenatal testicular patterning and angiogenesis. Interestingly, the DKK1 induced inhibition of testicular angiogenesis was rescued by the co-administration of R-spondin 1. In addition, R-spondin 1 alone was sufficient to enhance, in culture, testicular angiogenesis.

Vascular endothelial growth factor A: just one of multiple mechanisms for sex-specific vascular development within the testis?

“…Interestingly, RSPO1 can rescue DKK1 inhibition of angiogenesis indicating that perhaps RSPO1 is critical for necessary availability of PDGFB for endothelial cell branching during testis development. These actions of RSPO1 are thought to be mediated through beta catenin (CTNNB1) since testes treated in vitro with RSPO1 exhibit enhanced nuclear translocation of CTNNB1 which will affect gene expression within the nucleus (Caruso et al 2015). …”

Mesonephric Cell Migration into the Gonads and Vascularization Are Processes Crucial for Testis Development

“…4.4). In cultured explants of XY gonads/mesonephroi, DKK1 treatment inhibits endothelial cell migration into the gonad while RSPO1 treatment rescues this inhibition (Caruso et al 2015). Thus, molecules that promote mesonephric cell migration in the XY gonad such as SF1/CITED2 or RSPO1 have the opposite effect in the XX gonad and prevent ectopic vascularization.…”

“…In XY gonads of Rspo -/-mice testis morphogenesis appears normal, indicating that RSPO1 is not required in vivo for testis development (Chassot et al 2008;Lavery et al 2012). However, a recently published study shows that there may be a complex balance between RSPO1 and Dickkopf homolog 1 (DKK1), an inhibitor of the canonical WNT/RSPO signaling pathway regulating testicular angiogenesis with R-spondin 1 driving vascularization (Caruso et al 2015) (Fig. 4.4).…”

R-Spondin 1 Regulates WNT Signaling Pathway by Antagonizing the Function of Dickkopf Homolog 1

“…R-spondins (RSPOs) consisting of four members are a group of secreted proteins which could activate the canonical WNT/β-catenin-dependent signaling pathways [1]. Dickkopf homolog 1 (DKK1) is another important player, which is a well-known inhibitor of the canonical WNT signaling pathway [2]. More and more evidences declare that RSPO1 regulates WNT signaling by antagonizing the function of DKK1.…”

“…More and more evidences declare that RSPO1 regulates WNT signaling by inhibiting internalization of LRP6 via antagonizing the function of DKK1. DKK1 has the ability to form a complex between receptors to trigger LRP5/6 internalization [2]. It has been reported by Binnerts et al that RSPO1 could rescue the inhibition triggered by DKK1 [6].…”