Insulin-Like 3 Signaling Is Important for Testicular Descent but Dispensable for Spermatogenesis and Germ Cell Survival in Adult Mice1

Abstract

Relaxin family peptide receptor 2 (RXFP2) is the cognate receptor of a peptide hormone insulin-like 3 (INSL3). INSL3 is expressed at high levels in both fetal and adult Leydig cells. Deletion of Insl3 or Rxfp2 genes in mice caused cryptorchidism resulting from a failure of gubernaculum development. Using a novel mouse transgenic line with a knock-in LacZ reporter in the Rxfp2 locus, we detected a robust Rxfp2 expression in embryonic and early postnatal gubernaculum in males and in postmeiotic spermatogenic cells in adult testis. To study the role of INSL3/RXFP2 signaling in male reproduction, we produced a floxed Rxfp2 allele and used the Cre/loxP approach to delete Rxfp2 in different tissues. Using Cre transgene driven by retinoic acid receptor beta promoter, conditional gene targeting in gubernacular mesenchymal cells at early embryonic stages caused high intraabdominal cryptorchidism as in males with a global deletion of Rxfp2. However, when the Rxfp2 was deleted in gubernacular smooth or striated muscle cells, no abnormalities of testicular descent or testis development were found. Specific ablation of Rxfp2 in male germ cells using Stra8-icre transgene did not affect testis descent, spermatogenesis, or fertility in adult males. No significant change in germ cell apoptosis was detected in mutant males. In summary, our data indicate that the INSL3/RXFP2 signaling is important for testicular descent but dispensable for spermatogenesis and fertility in adult males.

Dynamics of insulin-like factor 3 and its receptor expression in boar testes

“…In adult rats, Rxfp2 transcripts are localized in spermatocytes, and injection of INSL3 into testes treated with a GnRH antagonist was shown to suppress germ cell apoptosis, suggesting that INSL3 acts through RXFP2 on germ cells and thereby contributes to spermatogenesis as a survival factor for male germ cells (Kawamura et al 2004). However, a more recent study in conditional Rxfp2 knockout mice, in which the gene was specifically deleted in later stages of postmeiotic germ cells, INSL3-RXFP2 signaling was found to be dispensable for spermatogenesis and male fertility (Huang et al 2012).…”

Insulin-like factor 3 as a monitor of endocrine disruption

“…Later studies on rats then showed that the cryptorchidism and other TDS-like effects induced in rats by administering phthalates during a critical window of testis differentiation also led to a marked downregulation of fetal Insl3 expression (McKinnell et al 2005, Mahood et al 2006. Combined with the knowledge from the mouse knockout studies, where either INSL3 or its receptor RXFP2 had been ablated leading to primary cryptorchidism (Nef & Parada 1999, Zimmermann et al 1999, Huang et al 2012, this placed INSL3 firmly within the signaling pathways, together with altered androgen production, linking endocrine disruptors to TDS-like defects -at least in rodents. …”

International Union of Basic and Clinical Pharmacology. XCV. Recent Advances in the Understanding of the Pharmacology and Biological Roles of Relaxin Family Peptide Receptors 1–4, the Receptors for Relaxin Family Peptides

“…However, it should be noted that androgen production is normal in INSL3 and RXFP2 knockout mice (Nef and Parada, 1999;Zimmermann et al, 1999;Overbeek et al, 2001;Gorlov et al, 2002). Additionally, conditional deletion of RXFP2 in male germ cells resulted in normal fertility (Huang et al, 2012).…”