Letter | Published:

A relative shift in cloacal location repositions external genitalia in amniote evolution

Nature volume 516, pages 391394 (18 December 2014) | Download Citation

This article has been updated

Abstract

The move of vertebrates to a terrestrial lifestyle required major adaptations in their locomotory apparatus and reproductive organs. While the fin-to-limb transition has received considerable attention1,2, little is known about the developmental and evolutionary origins of external genitalia. Similarities in gene expression have been interpreted as a potential evolutionary link between the limb and genitals3,4,5,6; however, no underlying developmental mechanism has been identified. We re-examined this question using micro-computed tomography, lineage tracing in three amniote clades, and RNA-sequencing-based transcriptional profiling. Here we show that the developmental origin of external genitalia has shifted through evolution, and in some taxa limbs and genitals share a common primordium. In squamates, the genitalia develop directly from the budding hindlimbs, or the remnants thereof, whereas in mice the genital tubercle originates from the ventral and tail bud mesenchyme. The recruitment of different cell populations for genital outgrowth follows a change in the relative position of the cloaca, the genitalia organizing centre. Ectopic grafting of the cloaca demonstrates the conserved ability of different mesenchymal cells to respond to these genitalia-inducing signals. Our results support a limb-like developmental origin of external genitalia as the ancestral condition. Moreover, they suggest that a change in the relative position of the cloacal signalling centre during evolution has led to an altered developmental route for external genitalia in mammals, while preserving parts of the ancestral limb molecular circuitry owing to a common evolutionary origin.

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Change history

  • 17 December 2014

    Ref. 48 was corrected.

Accessions

Primary accessions

Gene Expression Omnibus

Data deposits

Sequencing data has been deposited in the Gene Expression Omnibus under accession number GSE60373.

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Acknowledgements

The authors thank D. Duboule, H. Kaessmann, A. Necsulea, B. Okaty, G. Rey and G. P. Wagner for discussions, M. A. de Bakker for the snake Tbx5 probe and A. M. Herrera and M. J. Cohn for discussing and sharing unpublished results. μCT scans were performed at the Center for Nanoscale Systems, Harvard University (supported by National Science Foundation award ECS-0335765) and at the Museum of Comparative Zoology. Next-generation sequencing was performed at the HMS Biopolymers Facility and computational analyses were run on the Orchestra Cluster, HMS Research Computing. P.T. was supported by post-doctoral fellowships from the Swiss National Science Foundation, EMBO and the Human Frontiers Science Program. A.C.G. was supported by a post-doctoral fellowship from the Swiss National Science Foundation. This work was supported by National Institutes of Health grant R37-HD032443 to C.J.T.

Author information

Author notes

    • Emma Sherratt
    • , Thomas J. Sanger
    •  & Jimmy K. Hu

    Present addresses: Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, Iowa 50011, USA (E.S.); Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, Florida 32610, USA (T.J.S.); Department of Orofacial Sciences and Program in Craniofacial and Mesenchymal Biology, UCSF, San Francisco, California 94143, USA (J.K.H.).

Affiliations

  1. Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA

    • Patrick Tschopp
    • , Ariel C. Aspiras
    • , Jimmy K. Hu
    • , Olivier Pourquié
    •  & Clifford J. Tabin
  2. Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA

    • Emma Sherratt
    •  & Thomas J. Sanger
  3. Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115, USA

    • Anna C. Groner
  4. Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), 67400 Illkirch, France

    • Olivier Pourquié
  5. Department of Pathology, Brigham and Women’s Hospital, Boston, Massachusetts 02115, USA

    • Olivier Pourquié
  6. Developmental and Stem Cell Biology Department, Institut Pasteur, 75724 Paris Cedex 15, France

    • Jérôme Gros

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Contributions

P.T., J.G. and C.J.T. conceived the project and designed the experiments. P.T. performed most experiments and computational analyses. E.S. prepared CT scans and helped with statistical analyses. T.J.S. helped with CT scans, Anolis husbandry and embryo collection. A.C.G. produced lentiviruses and A.C.A. helped with grafting experiments. J.K.H., O.P. and J.G. initiated snake analyses. O.P. contributed snake embryos. J.G. contributed to chick lineage tracing experiments. P.T., J.G. and C.J.T. wrote the paper, with comments from co-authors.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Jérôme Gros or Clifford J. Tabin.

Extended data

Supplementary information

PDF files

  1. 1.

    Supplementary Table 1

    This file contains a list of orthologous genes between mouse and anole employed for GO-term analysis. Genes are ordered according to their absolute loading value from principal component analysis (see Fig. 3e), for principal component 2 (PC2), and top 500 genes (in bold, see Fig. 3f) were used for GO-term enrichment analysis.

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DOI

https://doi.org/10.1038/nature13819

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