Molecular analysis of the sex chromosomes of the platyfish Xiphophorus maculatus: Towards the identification of a new type of master sexual regulator in vertebrates

Abstract

In contrast to mammals and birds, fish display an amazing diversity of genetic sex determination systems, with frequent changes during evolution possibly associated with the emergence of new sex chromosomes and sexdetermining genes. To better understand the molecular and evolutionary mechanisms driving this diversity, several fish models are studied in parallel. Besides the medaka (Oryzias latipes Temminck and Schlegel, 1846) for which the master sex-determination gene has been identified, one of the most advanced models for studying sex determination is the Southern platyfish (Xiphophorus maculatus, Günther 1966). Xiphophorus maculatus belongs to the Poeciliids, a family of live-bearing freshwater fish, including platyfish, swordtails and guppies that perfectly illustrates the diversity of genetic sex-determination mechanisms observed in teleosts. For X. maculatus, bacterial artificial chromosome contigs covering the sex-determination region of the X and Y sex chromosomes have been constructed. Initial molecular analysis demonstrated that the sex-determination region is very unstable and frequently undergoes duplications, deletions, inversions and other rearrangements. Eleven gene candidates linked to the master sexdetermining gene have been identified, some of them corresponding to pseudogenes. All putative genes are present on both the X and the Y chromosomes, suggesting a poor degree of differentiation and a young evolutionary age for platyfish sex chromosomes. When compared with other fish and tetrapod genomes, syntenies were detected only with autosomes. This observation supports an independent origin of sex chromosomes, not only in different vertebrate lineages but also between different fish species.

Worthless and Nutritive Nuptial Gifts: Mating Duration, Sperm Stored and Potential Female Decisions in Spiders

“…All mating experiments were carried out during October-December 2012. A virgin female was placed in a transparent plastic cage (30 cm diameter and 10 cm height) with pebbles covering the bottom one day before the experiment, allowing her to deposit silk threads which are important stimuli for male courtship [ 43 ]. We then exposed each female to one male carrying a wrapped housefly (Fly gift-interrupted and uninterrupted mating), or a wrapped exoskeleton (Worthless gift-uninterrupted mating), or no gift (No-fly gift-interrupted mating).…”

Expression and Sequence Evolution of Aromatase cyp19a1 and Other Sexual Development Genes in East African Cichlid Fishes

“…Four of these genes, DMY/dmrt1bY , Gsdf Y , amhy and amhr2 , exemplify the scenario that genes already implicated downstream in a network (such as the genetic cascade of sex determination) are more readily uprecruited to the top of the hierarchy than nonimplicated genes—a hypothesis originally proposed by Wilkins (1995). Sex determination and differentiation have also been studied in various other model fish species including zebrafish (Anderson et al 2012), the poeciliid fishes guppy (Tripathi et al 2009) and platyfish (Böhne et al 2009), with a main focus on understanding and characterizing the genetic control over the establishment of the two sexes. Also, the downstream factors or particular genetic pathways of, for example, gonad development have been studied in several species (for review see Nakamura 2010; Angelopoulou et al 2012).…”

Estudio de la perturbación del desarrollo sexual de Cnesterodon decemmaculatus (Pisces, Poeciliidae) por compuestos con actividad estrogénica

“…Los poecílidos son una de las familias de peces más estudiadas con respecto a la determinación genética del sexo y la selección sexual, ilustrando perfectamente la diversidad de mecanismos observados en los teleósteos (Böhne et al, 2009). En esta familia se han descripto distintos tipos de sistemas genéticos de determinación del sexo, incluyendo tanto heterogamia masculina como femenina (Kallman, 1984;Volff y Schartl, 2001Schultheis et al, 2009).…”

“…nigrensis, X. cortezi, X. nezahualcoyotl y X. milleri (Böhne et al, 2009). Es importante destacar que especies filogenéticamente relacionadas, o incluso en diferentes poblaciones dentro de una misma especie, pueden observarse diferentes sistemas de determinación sexual.…”

“…Como se mencionó anteriormente, los poecílidos presentan una gran diversidad de mecanismos de determinación genética del sexo, y se han documentado especies con heterogamia femenina y otras con heterogamia masculina (Böhne et al, 2009;Schultheis et al, 2009). Por ello, sería interesante trabajar sobre aquellos genes que determinan y/o diferencian el sexo en C. decemmaculatus y relacionarlos con el sexo gonadal, aunque puede no ser trivial.…”