Biology Reference
In-Depth Information
system without having to dissect them. Analysis of their mutations has
demonstrated the value of the system for genetic dissection of vertebrate
development and diseases (Talbot and Hopkins, 2000).
In vertebrates, maternal genes direct fertilization, egg activation, the fi rst
cell division(s) and initiation of zygote transcription (Dorsch et al., 2004).
In amphibians and fi shes, the Animal-Vegetal pole (AV) or prospective
anterior-posterior axis is already established during oogenesis, as evidenced
by the asymmetric localization of germinal vesicle (King et al., 1999; Suzuki
et al., 2000). The dorso-ventral axis, established during embryonic cleavage,
also relies on maternal gene products. Thus the maternal genes and their
products lay the foundation for embryonic development, on which zygotic
factors build upon later. For example, Dorsch et al. (2004) have identifi ed
68 maternal effect mutants in zebrafi sh. Of them 15 are described to control
the formation of blastodisc, embryonic polarity, initiation of cell cleavage
and division (Table 30). Incidentally, Araki et al. (2001) have shown that
Table 30.
Selected maternal genes and their role in early embryonic development in zebrafi sh
(compiled from Dorsch et al., 2004 and others)
Classes of mutants and their
location in chromosomes
(chr)
Reported observations
Opaque egg
Ruehrei
p25ca
on chr 6
over easy
p37ad
sunny side up
p144de
on chr 22
souffl e
p96rc
on chr 16
These eggs fail to segregate cytoplasm to animal pole
and to form bastodisc. The failure is due to defective
oogenesis during stage IV
Egg activation and cytoplasmic segregation
Jumpostart
p108re
p11cv
Egg activation includes fusion of cortical granules to
the egg membrane. Release of their contents results in
chorion hardening
One or more of these events fail. Involved in activation
and formation of microfi lament required for blastodisc
formation
Animal-Vegetal polarity
Emulsion
p41p1
on chr 4 dp
14nb
Buck ball
p106re
p6cv
Wrong localizations of
cyclinB
mRNA in animal pole and
Bruno-like
in vegetal pole. Responsible for streaming of
cytoplasm and consequent cytoplasmic segregation to the
animal and vegetal poles. Cold shock affects cytoplasmic
tubulin formation
Failure to initiate cleavage
atomos
p71fm
on chr 9
indivisible
p15dia
irreducible
p15mf
on ch 20
Responsible for initiation of cytokinesis and karyokinesis.
Indivisible eggs
are fertilizable but do not initiate cleavage
Incomplete cellurization
Cellular island
p63cd
cellular atol
p57mfa
on chr 22
Responsible for completion of cleavage. Mutants cause
failure of cytokinesis but karyokinesis proceeds leading
to the formation syncytium, as in
cei
nuclei
