Gene amplification and functional diversification of melanocortin 4 receptor at an extremely polymorphic locus controlling sexual maturation in the platyfish.
In two swordtail species of the genus Xiphophorus, the onset of puberty has been shown to be modulated at the P locus by sequence polymorphism and gene copy-number variation affecting the type 4 melanocortin hormone receptor Mc4r. The system works through the interaction of two allelic types, one encoding wild type and the other dominant-negative receptors. We have analyzed the structure and evolution of the P locus in the platyfish Xiphophorus maculatus, where as many as nine alleles of P determining the onset of sexual maturity in males and females, fecundity in females, and adult size in males are located on both the X and Y chromosomes in a region linked to the master sex-determining locus. In this species, mc4r has been amplified to up to 10 copies on both the X and Y chromosomes through recent large serial duplications. Subsequently, mc4r paralogues have diverged considerably into many different subtypes. Certain copies have acquired new untranslated regions through genomic rearrangements, and transposable element insertions and other mutations have accumulated in promoter regions, possibly explaining observed deviations from the classical mc4r transcriptional pattern. In the mc4r-coding sequence, in-frame insertions and deletions as well as nonsense and missense mutations have generated a high diversity of Mc4r-predicted proteins. Most of these variants are expressed in embryos, adults, and/or tumors. Functional receptor characterization demonstrated major divergence in pharmacological behavior for Mc4r receptors encoded by different copies of platyfish mc4r, with differences in constitutive activity as well as binding and stimulation by hormones. The high degree of allelic and copy-number variation observed between individuals can explain the high level of polymorphism for sexual maturation, fecundity, and body size in the platyfish: multiple combinations of Mc4r variants with different biochemical properties might interact to modulate the melanocortin signaling that regulates the hypothalamus-pituitary-gonadal axis.
Institut de Génomique Fonctionnelle de Lyon, Ecole Normale Supérieure de Lyon-Centre National de la Recherche Scientifique UMR5242-Université Claude Bernard Lyon I, F-69364 Lyon Cedex 07, France.
Jean-Nicolas
JN
Volff
Yvonne
Y
Selz
Carsten
C
Hoffmann
Alexander
A
Froschauer
Christina
C
Schultheis
Cornelia
C
Schmidt
Qingchun
Q
Zhou
Wolfgang
W
Bernhardt
Reinhold
R
Hanel
Astrid
A
Böhne
Frédéric
F
Brunet
Béatrice
B
Ségurens
Arnaud
A
Couloux
Sylvie
S
Bernard-Samain
Valérie
V
Barbe
Catherine
C
Ozouf-Costaz
Delphine
D
Galiana
Martin J
MJ
Lohse
Manfred
M
Schartl
D000595:Amino Acid Sequence; D000818:Animals; D003532:Cyprinodontiformes / Q000235:genetics* / Q000378:metabolism; D004251:DNA Transposable Elements; D005260:Female; D005784:Gene Amplification; D015321:Gene Rearrangement; D056426:Genetic Loci; D016678:Genome; D057809:HEK293 Cells; D006801:Humans; D054643:INDEL Mutation; D008297:Male; D008969:Molecular Sequence Data; D011110:Polymorphism, Genetic; D011485:Protein Binding; D044105:Receptor, Melanocortin, Type 4 / Q000235:genetics* / Q000378:metabolism; D012730:Sex Chromosomes / Q000235:genetics
D004251:DNA Transposable Elements; D044105:Receptor, Melanocortin, Type 4
duplication; fish; melanocortin receptor; sex chromosomes; sexual maturity