Biology Reference
In-Depth Information
to depend on temperature (Strussmann et al., 1998), as in zebrafi sh, has
shown that anti-apoptosis gene
pen-2
plays a specifi c role in protecting
germ cells from apoptosis (Fernandino et al., 2010; see also Silva et al.,
2008). Knockdown of
pen-2
strongly induces the p53-dependant apoptosis
cascade (Cambell et al., 2006). Further Fernandino et al. (2010) have also
observed a higher expression level of
amh
at masculinizing temperatures
than at feminizing temperatures during the gonadal differentiation. At
intermediate temperatures, the expression level of
amh
remains higher in
half of the larvae than in the others.
Cyp19a1
shows a reciprocal expression
pattern.
The zebrafi sh has been used as a model species to assess the effects
of endocrine and similar chemicals on reproduction. Yet the molecular
mechanisms controlling zebrafi sh reproduction are poorly understood.
Using a 17K oligo nucleotide microarray, Santos et al. (2007) have investigated
the molecular basis for the phenotypic specifi city between sexes, between
individuals within a sex and reproductive status of breeding zebrafi sh. The
gonadal transcriptome has been found to differ substantially between sexes.
Microarray analysis of individual gonad reveals the consistent expression of
about 8,769 genes in the gonads, from which 7,976 and 7,060 are consistently
expressed in ovaries and testes, respectively. Of them, statistical analysis
has identifi ed 2,940 genes that are differently expressed between males and
females; among these sex specifi c genes, 1,570 are overexpressed in females
and 1,370 in males. Gene ontological analysis has revealed that
sox11b,
sox21a
and
sox31
are overexpressed in ovaries; in contrast, the absence of
elevated expression of
sox9a
and the relative overexpression of
amh
and its
receptor in testes induce not only the differentiation and development of
testes but also the maintenance of the sexual dimorphism. Incidentally, the
overexpression of
foxl2
in ovaries may be related to suppression of biological
activity of androgens in this organ.
Among the genes differentially expressed between ovaries and testes
in the array dataset, 53 genes have been further identifi ed to show a 10-fold
difference in expression between sexes. A magnitude of 3,000-fold difference
in expression of some genes between the ovary and testis is likely to play a
crucial role in context of sex specifi c gonadal function. Variation between
gonadal transcriptomes of individual males is limited and may account for
the phenotypic difference in sperm quality, such as sperm motility. However,
the variation between individual females exceeds the levels observed for
the males. Within the growing follicles, two groups are identifi ed; the fi rst
one includes predominantly early oocytes undergoing oogenesis and the
second one comprises of vitelloginic follicles, requiring batteries of enzymes
(e.g., cathepsins) to process this large yolk precursor into small molecules,
which are stored within the oocytes to provide nutritional support for
the developing embryos. Cluster analysis of 13 genes selected from these
