AMHY and sex determination in egg-laying mammals
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Date
2025
Authors
Shearwin-Whyatt, L.
Fenelon, J.
Yu, H.
Major, A.
Qu, Z.
Zhou, Y.
Shearwin, K.
Galbraith, J.
Stuart, A.
Adelson, D.
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Genome Biology, 2025; 26(1):144-1-144-21
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Linda Shearwin-Whyatt, Jane Fenelon, Hongshi Yu, Andrew Major, Zhipeng Qu, Yang Zhou, Keith Shearwin, James Galbraith, Alexander Stuart, David Adelson, Guojie Zhang, Michael Pyne, Stephen Johnston, Craig Smith, Marilyn Renfree, Frank Grützner
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Abstract
Background Egg-laying mammals (monotremes) evolved multiple sex chromosomes independently of therian mammals and lack the sex-determining gene SRY. The Y-localized anti-Müllerian hormone gene (AMHY) is the candidate sex-determination gene in monotremes. Here, we describe the evolution of monotreme AMHX and AMHY gametologues and for the first time, investigate their expression during gonad sexual differentiation in a monotreme. Results Monotreme AMHX and AMHY have significant sequence divergence at the promoter, gene, and protein level, likely following an original allele inversion in the early stages of monotreme sex chromosome differentiation but retaining the conserved features of TGF-β molecules. We show that the expression of sexual differentiation genes in the echidna fetal gonad, including DMRT₁ and SOX₉, is significantly different from that of therian mammals. Importantly, AMHY is expressed exclusively in the male gonad during sexual differentiation consistent with a role as the primary sex-determination gene whereas AMHX is expressed in both sexes. Experimental ectopic expression of platypus AMHX or AMHY in the chicken embryo did not masculinize the female urogenital system, as does chicken AMH, a possible result of mammalian-specific changes to AMH proteins preventing function in the chicken. Conclusions Our results provide insight into the early steps of monotreme sex chromosome evolution and sex determination with developmental expression data strongly supporting AMHY as the primary male sex-determination gene of platypus and echidna.
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© The Author(s) 2025. Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/