MAFB is dispensable for the fetal testis morphogenesis and the maintenance of spermatogenesis in adult mice

Abstract

The transcription factor MAFB is an important regulator of the development and differentiation of various organs and tissues. Previous studies have shown that MAFB is expressed in embryonic and adult mouse testes and is expected to act as the downstream target of retinoic acid (RA) to initiate spermatogenesis. However, its exact localization and function remain unclear. Here, we localized MAFB expression in embryonic and adult testes and analyzed its gene function using Mafb-deficient mice. We found that MAFB and c-MAF are the only large MAF transcription factors expressed in testes, while MAFA and NRL are not. MAFB was localized in Leydig and Sertoli cells at embryonic day (E) 18.5 but in Leydig cells, Sertoli cells, and pachytene spermatocytes in adults. Mafb-deficient testes at E18.5 showed fully formed seminiferous tubules with no abnormal structure or differences in testicular somatic cell numbers compared with those of control wild-type mice. Additionally, the expression levels of genes related to development and function of testicular cells were unchanged between genotypes. In adults, the expression of MAFB in Sertoli cells was shown to be stage specific and induced by RA. By generating Mafbfl/fl CAG-CreER™ (Mafb-cKO) mice, in which Cre recombinase was activated upon tamoxifen treatment, we found that the neonatal cKO mice died shortly upon Mafb deletion, but adult cKO mice were alive upon deletion. Adult cKO mice were fertile, and spermatogenesis maintenance was normal, as indicated by histological analysis, hormone levels, and germ cell stage-specific markers. Moreover, there were no differences in the proportion of seminiferous stages between cKO mice and controls. However, RNA-Seq analysis of cKO Sertoli cells revealed that the down-regulated genes were related to immune function and phagocytosis activity but not spermatogenesis. In conclusion, we found that MAFB is dispensable for fetal testis morphogenesis and spermatogenesis maintenance in adult mice, despite the significant gene expression in different cell types, but MAFB might be critical for phagocytosis activity of Sertoli cells.

The Gene Toolkit Implicated in Functional Sex in Sparidae Hermaphrodites: Inferences From Comparative Transcriptomics

“…The analysis also revealed genes encoding for transcription factors such as Tgfb1, Tgfb3, Tcf7 , and Mafb , where the former is considered to be expressed by the Sertoli cells and may be important for spermatogenesis (Memon et al, 2008), while, regarding the latter, studies in mice show that it is indispensable for the fetal testis morphogenesis and the maintenance of spermatogenesis (Shawki et al, 2018). The female-biased gonochoristic-specific genes included, among others, the TATA binding proteins Taf8 and Taf15 , the cytochoromic enzymes Cyp20a and Spdl1 that is also a female-biased gene in the guppy, Poecilia reticulata (Sharma et al, 2014).…”

Expression dynamics of self-renewal factors for spermatogonial stem cells in the mouse testis

“…Blood vessels might also be included in the interstitial compartment. To conclude, it is most appropriate to purify the subsets of testis cells using fluorescence-activated cell sorting/magnetic-activated cell sorting in combination with a reporter strain animal [ 42 , 43 ].…”

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

“…In addition to immune cell expression, both MAFB and MAF are early markers of interstitial mesenchymal cells in both sexes [9], and in later stages of fetal development MAFB is expressed in both Leydig and Sertoli cells [39]. Knock-in mutant analyses and global conditional deletion of Mafb revealed that it was not required for fetal testicular differentiation or for maintenance of adult spermatogenesis [39]. However, multiple studies have suggested that Mafb and Maf have redundant or overlapping roles [27,41], perhaps due to similar and conserved DNA binding domains [38,42,43]; additionally, Mafb;Maf double homozygous knockout embryos have earlier embryonic lethality than other combinations of large Maf genes [44], indicating that these genes have essential, redundant roles in embryogenesis.…”

“…In mice, MAFB and MAF, but not MAFA, are expressed in the fetal gonad [9,39]. MAF is expressed in macrophages within the developing gonad-mesonephros complex [8], and MAFB has been well-characterized as a marker of monocyte-derived myeloid cells [29,40].…”