Loss ofMafbandMafdistorts myeloid cell ratios and disrupts fetal mouse testis vascularization and organogenesis

Abstract

Testis differentiation is initiated when Sry in pre-Sertoli cells directs the gonad toward a male-specific fate. Sertoli cells are essential for testis development, but cell types within the interstitial compartment, such as immune and endothelial cells, are also critical for organ formation. Our previous work implicated macrophages in fetal testis morphogenesis, but little is known about genes underlying immune cell development during organogenesis. Here we examine the role of the immune-associated genes Mafb and Maf in mouse fetal gonad development, and we demonstrate that deletion of these genes leads to aberrant hematopoiesis manifested by supernumerary gonadal monocytes. Mafb;Maf double knockout embryos underwent initial gonadal sex determination normally, but exhibited testicular hypervascularization, testis cord formation defects, Leydig cell deficit, and a reduced number of germ cells. In general, Mafb and Maf alone were dispensable for gonad development; however, when both genes were deleted, we observed significant defects in testicular morphogenesis, indicating that Mafb and Maf work redundantly during testis differentiation. These results demonstrate previously unappreciated roles for Mafb and Maf in immune and vascular development and highlight the importance of interstitial cells in gonadal differentiation.Summary statementDeletion of Mafb and Maf genes leads to supernumerary monocytes in fetal mouse gonads, resulting in vascular, morphogenetic, and differentiation defects during testicular organogenesis.

Testicular macrophages are recruited during a narrow time window by fetal Sertoli cells to promote organ-specific developmental functions

“…However, we observed numerous CD11b+ myeloid cells in the gonad- mesonephros border region. In our recently published results (25), gonads lacking Mafb and Maf (also called c-Maf ), encoding transcription factors required for monocyte/macrophage development (67–69), also exhibited extensive supernumerary CD11b+ cells, and we demonstrated that these CD11b+ myeloid cells are monocytes; however, F4/80+ macrophages were not affected in Maf and Mafb mutant gonads.…”

“…In addition, the reduction of steroidogenic gene expression in CSF1R-antibodyinjected E18.5 testes may be related to the enhanced phagocytic activity of repopulated excess testicular macrophages and monocytes. In Maf mutant fetal gonads, we also found there were numerous monocytes with a downregulation of many steroidogenic genes (25). Therefore, a balance between Leydig cell steroidogenesis and testicular macrophage proliferation is critical for testis development and function.…”

“…Additionally, testis cords in Maf mutant gonads were smaller, but likely due to a significant decrease in the number of germ cells (25). However, our current results and our previous study (21) showed that macrophage-depleted gonads, either by using CSF1R antibody injection or a Cx3cr1 creER ; Rosa -DTA ablation method, have a normal number of germ cells.…”

“…We have previously shown that macrophages are present in the early undifferentiated fetal gonad and YS hematopoietic precursors give rise to macrophages in the nascent fetal testis (21), and other recent reports have also examined the origins of testicular immune cells, implicating monocytes and other myeloid cell types (22–24). In terms of function, we demonstrated that fetal testicular macrophages are required for testis morphogenesis during initial gonadogenesis, likely through modulation of vascular development that is critical for the formation of testicular architecture (21, 25).…”

Lhx2 in germ cells suppresses endothelial cell migration in the developing ovary

“…Vascularization is crucial for the delivery of exogenous factors in the testicular compartments, in the initial organization of the testis cords, and also in the regulation of testis morphogenesis (Gu et al, 2021; Singh and Modi, 2020; Svingen and Koopman, 2013). It is also required for maintaining the interstitial progenitor population of the fetal Leydig cells (Gu et al, 2021; Kumar and DeFalco, 2018; Li et al, 2021).…”