Evolution and Development of Testis

A special issue of Genes (ISSN 2073-4425). This special issue belongs to the section "Molecular Genetics and Genomics".

Deadline for manuscript submissions: closed (2 February 2021) | Viewed by 21659

Special Issue Editors


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Guest Editor
Department of Genetics, University of Granada, E-18100 Granada, Spain
Interests: mouse genetics; sex determination; gonad differentiation; spermatogenesis; disorders of sexual development

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Guest Editor
Universidad de Granada, Granada, Spain
Interests: genetics of sexual development in mammals; study of true hermaphroditism in natural mammalian populations; genetic control of testicular regression in mammalian species with seasonal reproduction

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Guest Editor
Departamento de Genética e Instituto de Biotecnología, Universidad de Granada, 18016 Armilla, Granada, Spain
Interests: mammalian developmental genetics; mammalian sex determination; sex reversal; true hermafroditism; intersexuality; gonadal development; ovotestis development; gene expression; seasonal testis regression; genetic biodiversity

Special Issue Information

The testes are the male gonads, where both sperm and androgenic hormones are produced. Testicular anatomy is very similar in mammals, birds, and reptiles, including the presence of a permanent germinal epithelium inside seminiferous tubules and interstitial Leydig cells, but it greatly diverges in other vertebrates. Despite the fact that spermatogenesis is evolutionarily well conserved, the mechanisms of sex determination and testis differentiation are quite different among related taxa. The comparison of these molecular mechanisms among different taxonomic groups will help us to understand how a developmental system with a common function and many common regulatory elements may differ in how the gene regulation network is triggered in different organisms, and how new genes are incorporated at the top of a taxa-specific network. This network makes it possible for the embryonic gonad to differentiate into two different organs, an ovary or a testis, depending on a decision made during development. Recently, however, this decision is proving not to be definitive, because evidence is accumulating that key genes of the male and female pathways are necessary to maintain sex throughout life and avoid transdifferentiation.

In this Special Issue we aim to provide an up-to-date overview of the mechanisms of testis determination and differentiation among different vertebrates, focusing on the aspects that may improve our understanding of the evolution of testis development.

Prof. Francisco Javier Barrionuevo Jimenez
Prof. Dr. Prof. Miguel Burgos
Prof. Dr. Rafael Jiménez
Guest Editor

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Keywords

  • testis development
  • sexual differentiation
  • sex determination
  • evolution of sexual development
  • transdifferentiation
  • gonadal embryology
  • sex chromosomes

Published Papers (4 papers)

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Review

26 pages, 5898 KiB  
Review
Genetic Regulation of Avian Testis Development
by Martin Andres Estermann, Andrew Thomas Major and Craig Allen Smith
Genes 2021, 12(9), 1459; https://doi.org/10.3390/genes12091459 - 21 Sep 2021
Cited by 11 | Viewed by 5241
Abstract
As in other vertebrates, avian testes are the site of spermatogenesis and androgen production. The paired testes of birds differentiate during embryogenesis, first marked by the development of pre-Sertoli cells in the gonadal primordium and their condensation into seminiferous cords. Germ cells become [...] Read more.
As in other vertebrates, avian testes are the site of spermatogenesis and androgen production. The paired testes of birds differentiate during embryogenesis, first marked by the development of pre-Sertoli cells in the gonadal primordium and their condensation into seminiferous cords. Germ cells become enclosed in these cords and enter mitotic arrest, while steroidogenic Leydig cells subsequently differentiate around the cords. This review describes our current understanding of avian testis development at the cell biology and genetic levels. Most of this knowledge has come from studies on the chicken embryo, though other species are increasingly being examined. In chicken, testis development is governed by the Z-chromosome-linked DMRT1 gene, which directly or indirectly activates the male factors, HEMGN, SOX9 and AMH. Recent single cell RNA-seq has defined cell lineage specification during chicken testis development, while comparative studies point to deep conservation of avian testis formation. Lastly, we identify areas of future research on the genetics of avian testis development. Full article
(This article belongs to the Special Issue Evolution and Development of Testis)
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14 pages, 965 KiB  
Review
Sex Maintenance in Mammals
by Rafael Jiménez, Miguel Burgos and Francisco J. Barrionuevo
Genes 2021, 12(7), 999; https://doi.org/10.3390/genes12070999 - 29 Jun 2021
Cited by 11 | Viewed by 4037
Abstract
The crucial event in mammalian sexual differentiation occurs at the embryonic stage of sex determination, when the bipotential gonads differentiate as either testes or ovaries, according to the sex chromosome constitution of the embryo, XY or XX, respectively. Once differentiated, testes produce sexual [...] Read more.
The crucial event in mammalian sexual differentiation occurs at the embryonic stage of sex determination, when the bipotential gonads differentiate as either testes or ovaries, according to the sex chromosome constitution of the embryo, XY or XX, respectively. Once differentiated, testes produce sexual hormones that induce the subsequent differentiation of the male reproductive tract. On the other hand, the lack of masculinizing hormones in XX embryos permits the formation of the female reproductive tract. It was long assumed that once the gonad is differentiated, this developmental decision is irreversible. However, several findings in the last decade have shown that this is not the case and that a continuous sex maintenance is needed. Deletion of Foxl2 in the adult ovary lead to ovary-to-testis transdifferentiation and deletion of either Dmrt1 or Sox9/Sox8 in the adult testis induces the opposite process. In both cases, mutant gonads were genetically reprogrammed, showing that both the male program in ovaries and the female program in testes must be actively repressed throughout the individual’s life. In addition to these transcription factors, other genes and molecular pathways have also been shown to be involved in this antagonism. The aim of this review is to provide an overview of the genetic basis of sex maintenance once the gonad is already differentiated. Full article
(This article belongs to the Special Issue Evolution and Development of Testis)
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19 pages, 440 KiB  
Review
Testis Development and Differentiation in Amphibians
by Álvaro S. Roco, Adrián Ruiz-García and Mónica Bullejos
Genes 2021, 12(4), 578; https://doi.org/10.3390/genes12040578 - 16 Apr 2021
Cited by 13 | Viewed by 4133
Abstract
Sex is determined genetically in amphibians; however, little is known about the sex chromosomes, testis-determining genes, and the genes involved in testis differentiation in this class. Certain inherent characteristics of the species of this group, like the homomorphic sex chromosomes, the high diversity [...] Read more.
Sex is determined genetically in amphibians; however, little is known about the sex chromosomes, testis-determining genes, and the genes involved in testis differentiation in this class. Certain inherent characteristics of the species of this group, like the homomorphic sex chromosomes, the high diversity of the sex-determining mechanisms, or the existence of polyploids, may hinder the design of experiments when studying how the gonads can differentiate. Even so, other features, like their external development or the possibility of inducing sex reversal by external treatments, can be helpful. This review summarizes the current knowledge on amphibian sex determination, gonadal development, and testis differentiation. The analysis of this information, compared with the information available for other vertebrate groups, allows us to identify the evolutionarily conserved and divergent pathways involved in testis differentiation. Overall, the data confirm the previous observations in other vertebrates—the morphology of the adult testis is similar across different groups; however, the male-determining signal and the genetic networks involved in testis differentiation are not evolutionarily conserved. Full article
(This article belongs to the Special Issue Evolution and Development of Testis)
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Graphical abstract

23 pages, 2745 KiB  
Review
Diverse Regulation but Conserved Function: SOX9 in Vertebrate Sex Determination
by Brittany Vining, Zhenhua Ming, Stefan Bagheri-Fam and Vincent Harley
Genes 2021, 12(4), 486; https://doi.org/10.3390/genes12040486 - 26 Mar 2021
Cited by 28 | Viewed by 7319
Abstract
Sex determination occurs early during embryogenesis among vertebrates. It involves the differentiation of the bipotential gonad to ovaries or testes by a fascinating diversity of molecular switches. In most mammals, the switch is SRY (sex determining region Y); in other vertebrates it could [...] Read more.
Sex determination occurs early during embryogenesis among vertebrates. It involves the differentiation of the bipotential gonad to ovaries or testes by a fascinating diversity of molecular switches. In most mammals, the switch is SRY (sex determining region Y); in other vertebrates it could be one of a variety of genes including Dmrt1 or dmy. Downstream of the switch gene, SOX9 upregulation is a central event in testes development, controlled by gonad-specific enhancers across the 2 Mb SOX9 locus. SOX9 is a ‘hub’ gene of gonadal development, regulated positively in males and negatively in females. Despite this diversity, SOX9 protein sequence and function among vertebrates remains highly conserved. This article explores the cellular, morphological, and genetic mechanisms initiated by SOX9 for male gonad differentiation. Full article
(This article belongs to the Special Issue Evolution and Development of Testis)
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