Monday, 26 March 2012

The number of x-chromosomes in cells affects sexual behaviour


The number of x-chromosomes in cells affects sexual behaviour

Recent research undertaken by Paul  Bonthuis, Kimberly Cox and Emilie Rissman of the University of Virginia School of Medicine published in the journal, Hormones and Behaviour has found that mice models with two X-chromosomes, regardless of gender, exhibited significantly higher incidences of ‘masculine sexual behaviour’. The mice with two x-chromosomes of both sexes mounted and thrusted significantly more often than the mice with a single x-chromosome, while male double-x mice ejaculated faster and more frequently than the single-x mice [1].

It is well known that the x-chromosome encodes a very large number of genes, whereas the
y-chromosome encodes relatively few, all of which are unique to it. The Sry gene, found on the
y-chromosome encodes for the testes [5]. In the experiment the Sry gene was taken out of the
y-chromosome and copied onto an autosome. Inheritance of the modified autosome with the Sry gene resulted in four distinct groups XX males, XY males, XX females, XY females. The XX males had a modified form of the XX male syndrome [3] whereby instead of Sry expression on the x-chromosome it was instead expressed on an autosome. The XY female mice inherited the defunct y-chromosome without inheriting the Sry autosome resulting in mice with Turner Syndrome [4]. It was found that the XX males were possessed of more masculine sexual behaviour, consisting of faster ejaculation, more incidences of mounts and thrusts in both the male and female XX mice [1].

To determine whether it was the presence of the y-chromosome or the presence of the two x-chromosomes that caused these behaviours, a second group of mice we tested. These mice did not have the modified Sry autosome, however instead several groups were implanted with extra chromosomes. The four groups present were XY males, XXY males, XYX females, and XX females.  This allowed the mice to be differentiated into 1X-chromosome and 2X-chromosome groups, with the 2X mice suffering from Klinefelter’s Syndrome in males, and Klinefelter’s Syndrome-like symptoms in females [2]. Of the two groups the 2X mice had significantly more instances of ‘masculine sexual behaviour’ with a much larger number of 2X mice ejaculating during one or more of the trials. Similarly all of the 2X mice mounted and thrusted during all four of the trials compared to only half of the 1X. Despite the higher number of mounts, the number of ejaculations found were similar between 1X and 2X mice [1].


From the evidence of these two groups, it can be seen that the mice with two x-chromosomes regardless of the presence of a Sry modified autosome or a regular y-chromosome, display more masculine sexual behaviours, indeed females possessing two x-chromosomes displayed as many of these behaviours as did the male mice that possessed two x-chromosomes. The research team has speculated that there is a gene, that’s expression drastically affects the sexual behaviour of mice and maybe higher mammals [1].


Genotype
Gonads
Sry
Copies of Y
Copies of X
FCG





XYM
XY- Sry
Testes
1
1
1
XXM
XXSry
Testes
1
0
2
XYF
XY-
Ovaries
0
1
1
XXF
XX
Ovaries
0
0
2
Y*





1XM
XY*
Testes
1
1
1
2XM
XXY*
Testes
1
1
2
1XF
XY*X
Ovaries
0
0
1
2XF
XX
Ovaries
0
0
2
Table 1: Composition of sex chromosome regions in experimental mice.[1]

Reference List
[1] Bonthuis, P.J., et al., X-chromosome dosage affects male sexual behavior, Horm. Behav. (2012), doi:10.1016/j.yhbeh.2012.02.003
[2] Medscape: Medscape Access. 2012. Medscape: Medscape Access. [ONLINE] Available at: http://emedicine.medscape.com/article/945649-overview#a0104. [Accessed 19 March 2012].
[3] Clinical, Endocrinological, and Epigenetic Features of the 46,XX Male Syndrome, Compared with 47,XXY Klinefelter Patients . 2012. Clinical, Endocrinological, and Epigenetic Features of the 46,XX Male Syndrome, Compared with 47,XXY Klinefelter Patients . [ONLINE] Available at: http://jcem.endojournals.org/content/92/9/3458.full. [Accessed 19 March 2012].
[4] Turner syndrome - PubMed Health. 2012. Turner syndrome - PubMed Health. [ONLINE] Available at: http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001417/. [Accessed 19 March 2012].
[5] SRY: Sex determination - Genes and Disease - NCBI Bookshelf. 2012. SRY: Sex determination - Genes and Disease - NCBI Bookshelf. [ONLINE] Available at: http://www.ncbi.nlm.nih.gov/books/NBK22246/. [Accessed 19 March 2012].

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