Introduction
This page introduces the role of localized messenger RNA in regulating processes of development in the frog. This mechanism has been shown not only to
function in other species but is also seen as a mechanism within individual cells.
Some Recent Findings
Birsoy B, Kofron M, Schaible K, Wylie C, Heasman J.
Vg1 is an essential signaling molecule in Xenopus development.
Development. 2006 Jan;133(1):15-20. Epub 2005 Nov 24.
"Xenopus Vg1, a transforming growth factor beta (Tgfbeta) family member, was one of the first maternally localized mRNAs identified in vertebrates.
Its restriction to the vegetal pole of the egg made it the ideal candidate to be the mesoderm-inducing signal released by vegetal cells,
but its function in vivo has never been resolved. We show that Vg1 is essential for Xenopus embryonic development, and is required for mesoderm induction
and for the expression of several key Bmp antagonists. Although the original Vg1 transcript does not rescue Vg1-depleted embryos, we report that a second allele is effective.
This work resolves the mystery of Vg1 function, and shows it to be an essential maternal regulator of embryonic patterning."
De Robertis EM, Kuroda H.
Dorsal-ventral patterning and neural induction in Xenopus embryos.
Annu Rev Cell Dev Biol. 2004;20:285-308. Review.
References
PubMed
Requires internet connection.
Search PubMed:term=frog+development
| term=xenopus+development
Developmental Biology (6th ed) Gilbert:
Frog Life Cycle
Molecular Cell Biology (4th ed.)Lodish
Figure 23-5. Early embryogenesis of the frog Xenopus laevis
- Organisation of Xenopus oocyte and egg
cortices. Chang
P, Perez-Mongiovi D, Houliston E Microsc Res
Tech 1999 Mar 15;44(6):415-29
- Abstract: The division of the Xenopus
oocyte cortex into structurally and
functionally distinct "animal" and "vegetal"
regions during oogenesis provides the basis
of the organisation of the early embryo. The
vegetal region of the cortex accummulates
specific maternal mRNAs that specify the
development of the endoderm and mesoderm, as
well as functionally-defined "determinants"
of dorso-anterior development, and
recognisable "germ plasm" determinants that
segregate into primary germ cells. These
localised elements on the vegetal cortex
underlie both the primary animal-vegetal
polarity of the egg and the organisation of
the developing embryo. The animal cortex
meanwhile becomes specialised for the events
associated with fertilisation: sperm entry,
calcium release into the cytoplasm, cortical
granule exocytosis, and polarised cortical
contraction. Cortical and subcortical
reorganisations associated with meiotic
maturation, fertilisation, cortical rotation,
and the first mitotic cleavage divisions
redistribute the vegetal cortical
determinants, contributing to the
specification of dorso-anterior axis and
segregation of the germ line. In this article
we consider what is known about the changing
organisation of the oocyte and egg cortex in
relation to the mechanisms of determinant
localisation, anchorage, and redistribution,
and show novel ultrastructural views of
cortices isolated at different stages and
processed by the rapid-freeze deep-etch
method. Cortical organisation involves
interactions between the different
cytoskeletal filament systems and internal
membranes. Associated proteins and
cytoplasmic signals probably modulate these
interactions in stage-specific ways, leaving
much to be understood.
- Translocation of a
localized maternal mRNA to the vegetal pole of
Xenopus oocytes. Melton
DA Nature 1987 Jul 2-8;328(6125):80-2
- A key paper in establishing localization
of maternal mRNAs as regulators of
developmental pattern formation. This
localization of mRNAs has also been found for
many different drosophila (fly) mRNAs with
many different patterns.
- Abstract: A prominent hypothesis in
embryology is that localized maternal factors
are important in specifying cell fate. There
are, however, only a few examples of maternal
molecules that have been shown to be
localized and very little is known about how
such factors are physically localized within
an egg (for review see ref. 1). Previously,
cDNA clones were obtained for a class of
localized maternal mRNAs from Xenopus laevis.
These mRNAs are unusual in that they are
concentrated at either the animal or vegetal
pole of unfertilized eggs. In the present
study the synthesis and intracellular
distribution of one of them, Vg1, has been
examined during oogenesis. The results show
that Vg1 mRNA is localized as a crescent at
the vegetal pole of mature oocytes.
Surprisingly, this mRNA is uniformly
distributed in the cytoplasm of immature
oocytes. These findings suggest that a single
cell, the frog oocyte, has some mechanism for
translocating specific RNAs like Vg1. The
process that moves Vg1 mRNA is evidently a
cytoplasmic localization machinery which is
not directly coupled to the synthesis of Vg1
RNA.
- A two-step model for the localization of
maternal mRNA in Xenopus oocytes: involvement of
microtubules and microfilaments in the
translocation and anchoring of Vg1 mRNA.
Yisraeli
JK, Sokol S, Melton DA Development 1990
Feb;108(2):289-98.
- Abstract: In an effort to understand how
polarity is established in Xenopus oocytes,
we have analyzed the process of localization
of the maternal mRNA, Vg1. In fully grown
oocytes, Vg1 mRNA is tightly localized at the
vegetal cortex. Biochemical fractionation
shows that the mRNA is preferentially
associated with a detergent-insoluble
subcellular fraction. The use of cytoskeletal
inhibitors suggests that (1) microtubules are
involved in the translocation of the message
to the vegetal hemisphere and (2)
microfilaments are important for the
anchoring of the message at the cortex.
Furthermore, immunohistochemistry reveals
that a cytoplasmic microtubule array exists
during translocation. These results suggest a
role for the cytoskeleton in localizing
information in the oocyte.
- RNA sorting in
Xenopus oocytes and embryos. Mowry
KL, Cote CA FASEB J 1999
Mar;13(3):435-45
- mRNA localisation during
development. Micklem DR Dev Biol 1995
Dec;172(2):377-95.
- Thyroid hormone-dependent metamorphosis
in a direct developing frog. Callery, EM and
Elinson RP, Proc. Natl. Acad. Sci. USA, Vol. 97,
Issue 6, 2615-2620, March 14, 2000
- The direct developing anuran,
Eleutherodactylus coqui, lacks a tadpole,
hatching as a tiny frog. We investigated the
role of the metamorphic trigger, thyroid
hormone (TH), in this unusual ontogeny.
Expression patterns of the thyroid hormone
receptors, TR and TR, were similar to those
of indirect developers. TR mRNA levels
increased dramatically around the time of
thyroid maturation, when remodeling events
reminiscent of metamorphosis occur. Treatment
with the goitrogen methimazole inhibited this
remodeling, which was reinitiated on
cotreatment with TH. Despite their radically
altered ontogeny, direct developers still
undergo a TH-dependent metamorphosis, which
occurs before hatching. We propose a new
model for the evolution of anuran direct
development.
External WWW Links
Note the dynamic developmental nature of the Internet means that some links may not always work (search using the link term).
- Xenbase A database of information pertaining to the cell and developmental
biology of the frog, Xenopus
- Xenopus Laboratory List A database of Labs studying Xenopus
- Xenopus Microarrays
- Xenopus Cell Biology
- The
Xenopus Molecular Marker Resource
- An electronic library of information on
embryonic development of the frog, Xenopus
laevis.
- Index
page for all Markers
- It also contains a collection of
wholemount staining
patterns
- Molecular Markers of Development
- cement gland; XA,
XAG,
XCG
- early mesoderm; BMP2,
BMP4,
Chordin,
goosecoid,
Mix,
noggin, Xbra,
Xnr3,
Xwnt-8,
XVent1
and XVent2
- endothelial; Xl-fli
- germ cells; Xpat
- heart; cardiac
troponin I , XNKX-2.5,
XTin1
(XNKX-2.3)
- lateral line; tor70,
2G9
- muscle; 5A3,
12/101,
cardiac
actin, XMyf-5,
XMyoD
- neural crest; Slug,
XTwist
, xAP2
- notochord: Xnot,
tor70
- pronephros; 3G8
, Wilms'
tumor (xWT1), Xlim-1,
Xwnt-4
- pronephric duct; 4A6
- Frogs
of Greater Brisbane Region
(Australia)
- DNA SequenceXenopus laevis mitochondrial
DNA, complete genome- 17553 bp
- gi|343717|gb|M10217.1|XELMTCG
[343717] View GenBank
report
- The complete nucleotide sequence of
the Xenopus laevis mitochondrial genome.
Roe,B.A.,
Ma,D.P., Wilson,R.K. and Wong,J.F. J.
Biol. Chem. 260 (17), 9759-9774 (1985)
- Abstract: The complete sequence
of the 17,553-nucleotide Xenopus laevis
mitochondrial genome has been determined.
A comparison of this amphibian
mitochondrial genomic sequence with those
of the mammalian mitochondrial genomes
reveals a similar gene order and compact
genomic organization.
- Developmental Biology- Laurie Iten's
Serially
Sectioned Frog and Chick Embryos
- Developmental Biology- Jeff Hardin's
Amphibian
Embryology Tutorial
- NIH-
Organisms for biomedical research
Glossary of Terms
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Comments
This page introduces the role of localized (or localised) messenger RNA in the developmental process of the Frog.
Even today the entire process can be easily observed in the classroom using basically a small aquarium tank and eggs from a pond.
Please email Dr Mark Hill if you wish to make a comment about this current project.
