Effects of androgen and oestrogen on IGF pathways controlling phallus growth

Abstract

The development of the mammalian phallus involves hormone-dependent mesenchymal-epithelial signalling mechanisms that contribute to urethral closure and regulation of phallus elongation and growth. In marsupials, most differentiation and growth of the phallus occurs post-natally, making them amenable to direct hormone treatment. Expression of IGFs, FGFs, EFNB2, MAFB, DLX5 and AP-1 mRNAs in the phallus at day 50 post-partum (pp) were altered after treatment of tammar wallaby young from day 20 to 40 pp with androgen, oestrogen or after castration at day 25 pp. However, the most interesting changes occurred in the IGF pathway genes. Androgen treatment upregulated IGF1 in female phalluses and oestrogen treatment upregulated IGF1 in male phalluses, but it was downregulated by castration. IGFBP3 was higher in female phalluses and downregulated by androgen. IGF1 expression was higher in all untreated male than in female phalluses from day 50 to 150 pp, but IGFBP3 had the reverse pattern. At day 90 pp, when urethral closure in males is progressing and male phallus growth is accelerating. IGF1 and PCNA protein were only detected in the male urorectal septum, suggesting for the first time that closure and elongation may involve IGF1 activation of cell proliferation specifically in male phalluses. These effects of sex steroids on gene expression and on the IGF1 signalling pathway in particular, suggest that the developing phallus may be especially susceptible to perturbation by exogenous hormones.Reproduction (2019) 157 1-12

Transcriptomic Analysis of MAP3K1 and MAP3K4 in the Developing Marsupial Gonad

“…The tammar gonadal transcriptome data confirm our previous qPCR study of changes in sexual differentiation genes after oestrogen treatment [Pask et al, 2010;Chen et al, 2018]. During testicular differentiation in the tammar, transcriptome expressions of SOX9 and AMH were similar to those of the mouse [Jameson et al, 2012] although extending over a longer time period consistent with the slower process of gonadal differentiation in tammars.…”

Hormonal and Molecular Regulation of Phallus Differentiation in a Marsupial Tammar Wallaby

“…In the tammar, both SHH and MAFB are higher in normal female phalluses and are increased in phalluses after castration in males at day 50 pp [15]. This is in contrast to our expectation due to the predominant role of Mafb in male phalluses in mice [23][24][25].…”

“…Through steroid treatment and RNA-sequencing (RNA-seq) data analysis in the tammar, a number of genes are shown to have a similar expression pattern to that of SHH. SHH, Wnt family member 5A (WNT5A), and MAF BZIP transcription factor B (MAFB) are all downregulated in female phalluses by androgen treatment at day 50 pp, but are upregulated after castration in males [13,15], while fibroblast growth factor 10 (FGF10) is upregulated by androgen treatment, but downregulated after castration in males [15]. The development of male tammar phallus is androgen dependent [5,6], like that of eutherian mammals.…”

“…In the tammar, FGF10 expression is upregulated by androgen [15], unlike SHH, WNT5A, and MAFB that are downregulated [13,15]. In mice, high levels of SHH inhibits FGF10 transcription in the endoderm during lung morphogenesis [26].…”

“…In the tammar, a transient high level of SHH in male phalluses at day 50 pp (mentioned above) may suppress FGF10 expression. When SHH decreases after day 50 pp [9], FGF10 increases [15]. Therefore, it is possible that SHH signalling suppresses FGF10 expression at day 50 pp before phallus elongation.…”