Biology Reference
In-Depth Information
Table 1. Main characteristics and differences between mammals and teleost fi shes regarding
gonadal differentiation (from Mouriec et al. 2009; Le Page et al., 2010; condensed)
Mammals
Teleosts
1. Sex determination
Genetic determination only
Genetic determination only in a couple of
medaka
Sry is the only master male
determining gene
Many others, temperature, hypoxia, density,
social environment also determine sex
2. Neurogenic activity
High during development only
High throughout development and adult life
3. Hormones
(i) Testosterone
Crucial for brain masculinization,
Stimulates secondary sexual characters
Not a male specifi c hormone
Involved in fi nal maturation of ♂ and ♀
(ii) Estrogen
Required for brain feminization via
testosterone aromatization, regulation
of ovarian cycle
Triggering and maintenance of ovarian
differentiation, stimulates vitellogenesis,
strongly up-regulates brain aromatase
(iii) 11-Ketotestosterone
Not present
Key androgen hormone in most fi shes, involved
in testis differentiation
(iv) 11β Hydroxy testosterone
Not present
Key androgen hormone in some fi shes, involved
in testis differentiation, stimulates secondary
sexual characteristics, modulates adult sexual
behaviour
(v) Aromatase
One aromatase gene but different
expression regulated at promoter
level. Low expression in testis, high
expression in ovary and associated
functions
Gonad specifi c gene cyp19a1a . Down- regulated
during testis differentiation, up-regulated during
ovary and associated functions
(vi) Aromatase in brain
Key role in brain sexualization
during prenatal period but moderate
expression in adult. Mainly expressed
in neurons. Radial glial cells disappear
following embryonic neurogenesis
Extraordinarily high levels (100 to 1000 fold)
brain specifi c cyp19a1b. Involved in brain
sexualization throughout life. cyp19a1b activity
restricted to radial glial cells from forebrain. Low
expression on embryos but high in adults of both
sexes
located on different chromosomes. For instance, a QTL sex determining gene
is linked to another QTL for body size in Sparus aurata (Loukovitis et al.,
2011) and Dmrt1 is located on chromosome 5 and cyp21a2 on chromosome
16 in Danio rerio (Bradley et al., 2011). Hence this presentation emphasizes
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