(发育生物学)III 生殖细胞发生与受精
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In mice, At day 6.5 of embryonic development, BMP4/BMP8b from the extraembryonic ectoderm give certain cells in this area the ability to produce germ cells.
The pole plasm at the posterior pole is critical for determination of the PGCs
The molecular mechanisms underlying the specification and determination of the PGCs in Drosophila
Specification and determination of the PGCs
Gametes in all sexually reproducing organisms arise from the primordial germ cells (PGCs).
In many instances (including nematodes, flies, and frogs ), the PGCs are specified and determined autonomously by the cytoplasmic determinants in the early embryos that are comprised of specific proteins and mRNAs. These cytoplasmic determinants are collectively referred to as the germ plasm（生殖质）(The cell-autonomous manner)
Specification and determination of the PGCs
Germ plasm can be identified morphologically by the presence of conspicuous membrane-unbound organelles with an electron-dense granulofibrillar appearance called germ granules
The pole plasm includes several components that are crucial for the PGC determination. Those are Oskar, Nanos, Vasa, mRNA of gcl (germ cell less) gene, mitochondrial ribosomal RNA (mtr RNA) etc
There is no evidence for germ plasm being involved in germ cell formation in the mouse or other mammals. Instead, germ cell specification in the mouse involves cell induction (cell-cell interactions).
2 Gametogenesis
2.1 Spermatogenesis 2.2 Oogenesis
3 Fertilization
3.1 The recognition of egg and sperm 3.2 The prevention of polyspermy 3.3 The activation of egg metabolism
(发育生物学）III 生殖细胞发生与受精
The germ cell development and fertilization
Questions need to be addressed: ➢ How are the germ cells specified and determined? ➢ How are the primordial germ cells (PGCs) differentiated into eggs and sperm? (including meiosis) ➢ Fertilization and activation of the egg by the sperm that initiates the embryonic development.
Mutations in any of those genes, e.g oskar, result in the affected homozygous females being “grandchildless”. The mutant female does not produce functional pole plasm in her eggs, thus having offsprings (F1) who lack germ cells and therefore are sterile (no F2 offsprings).
P4 blastomere is the PGC
Origin of the PGCs in Drosophila
The PGCs known as pole cells become distinct at the posterior pole of the egg about 90 minutes after fertilization. The cytoplasm at the posterior pole is called pole plasm (极质) and is distinguished by large organelles, the polar granules.
Origin of the PGCs in Drosophila
The PGCs known as pole cells become distinct at the posterior pole of the egg about 90 minutes after fertilization. The cytoplasm at the posterior pole is called pole plasm (极质) and is distinguished by large organelles, the polar granules. The role of pole plasm in PGC determination: ✓ No germ cells develop if the posterior end of the egg is irradiated with ultraviolet light ✓ If pole plasm of an egg is transferred to the anterior pole of another embryo, the nuclei surrounded by the pole plasm at the anterior pole are specified as germ cells
The germ cell development and fertilization
1 The germ cell fate determi Specification and determination of the primordial germ cells (PGCs) 1.2 The germ cell migration and development of gonads
Posterior granules (P granules) in C. elegans Polar granules( P granules) in Drosophila Germinal granules in Xenopus
The germ cell fate of C. elegans is determined at the 16-cell embryo
Germ cell specification in the mouse involves cell-cell interactions
Expression of oskar alone is sufficient for ectopically specifying the germ cells
The gene oskar is sufficient to specify the germ cells in Drosophila
The germ cell development and fertilization
1 The germ cell fate determination and development of gonads
1.1 Specification and determination of the primordial germ cells (PGCs) 1.2 The germ cell migration and development of gonads
2 Gametogenesis
2.1 Spermatogenesis 2.2 Oogenesis
3 Fertilization
3.1 The recognition of egg and sperm 3.2 The prevention of polyspermy 3.3 The activation of egg metabolism
In other instances (such as salamanders蝾螈 and mammals), the PGCs are specified by cell induction via neighboring cells. (The non cell-
autonomous manner)
Functionally conserved genes in Germ-Cell Development
Origin of the PGCs in mammals
There is no obvious germ plasm in mammals, and mammalian germ cells are not morphologically distinct during early development. Rather, germ cells are induced in gastrulating embryos In mice, the germ cells form at the posterior region of the epiblast, at the junction of the extraembryonic ectoderm, epiblast, primitive streak, and allantois (尿囊).
The mammalian PGCs appear to be induced in the early gastrulating embryos
The molecular mechanisms underlying the specification and determination of the PGCs in Mammals
So far, it has been reported that several maternal gene (at least 8 genes) are functionally necessary and sufficient for the pole plasm formation, and the germ cell specification/determination
The pole plasm at the posterior pole is critical for determination of the PGCs
The molecular mechanisms underlying the specification and determination of the PGCs in Drosophila
Specification and determination of the PGCs
Gametes in all sexually reproducing organisms arise from the primordial germ cells (PGCs).
In many instances (including nematodes, flies, and frogs ), the PGCs are specified and determined autonomously by the cytoplasmic determinants in the early embryos that are comprised of specific proteins and mRNAs. These cytoplasmic determinants are collectively referred to as the germ plasm（生殖质）(The cell-autonomous manner)
Specification and determination of the PGCs
Germ plasm can be identified morphologically by the presence of conspicuous membrane-unbound organelles with an electron-dense granulofibrillar appearance called germ granules
The pole plasm includes several components that are crucial for the PGC determination. Those are Oskar, Nanos, Vasa, mRNA of gcl (germ cell less) gene, mitochondrial ribosomal RNA (mtr RNA) etc
There is no evidence for germ plasm being involved in germ cell formation in the mouse or other mammals. Instead, germ cell specification in the mouse involves cell induction (cell-cell interactions).
2 Gametogenesis
2.1 Spermatogenesis 2.2 Oogenesis
3 Fertilization
3.1 The recognition of egg and sperm 3.2 The prevention of polyspermy 3.3 The activation of egg metabolism
(发育生物学）III 生殖细胞发生与受精
The germ cell development and fertilization
Questions need to be addressed: ➢ How are the germ cells specified and determined? ➢ How are the primordial germ cells (PGCs) differentiated into eggs and sperm? (including meiosis) ➢ Fertilization and activation of the egg by the sperm that initiates the embryonic development.
Mutations in any of those genes, e.g oskar, result in the affected homozygous females being “grandchildless”. The mutant female does not produce functional pole plasm in her eggs, thus having offsprings (F1) who lack germ cells and therefore are sterile (no F2 offsprings).
P4 blastomere is the PGC
Origin of the PGCs in Drosophila
The PGCs known as pole cells become distinct at the posterior pole of the egg about 90 minutes after fertilization. The cytoplasm at the posterior pole is called pole plasm (极质) and is distinguished by large organelles, the polar granules.
Origin of the PGCs in Drosophila
The PGCs known as pole cells become distinct at the posterior pole of the egg about 90 minutes after fertilization. The cytoplasm at the posterior pole is called pole plasm (极质) and is distinguished by large organelles, the polar granules. The role of pole plasm in PGC determination: ✓ No germ cells develop if the posterior end of the egg is irradiated with ultraviolet light ✓ If pole plasm of an egg is transferred to the anterior pole of another embryo, the nuclei surrounded by the pole plasm at the anterior pole are specified as germ cells
The germ cell development and fertilization
1 The germ cell fate determi Specification and determination of the primordial germ cells (PGCs) 1.2 The germ cell migration and development of gonads
Posterior granules (P granules) in C. elegans Polar granules( P granules) in Drosophila Germinal granules in Xenopus
The germ cell fate of C. elegans is determined at the 16-cell embryo
Germ cell specification in the mouse involves cell-cell interactions
Expression of oskar alone is sufficient for ectopically specifying the germ cells
The gene oskar is sufficient to specify the germ cells in Drosophila
The germ cell development and fertilization
1 The germ cell fate determination and development of gonads
1.1 Specification and determination of the primordial germ cells (PGCs) 1.2 The germ cell migration and development of gonads
2 Gametogenesis
2.1 Spermatogenesis 2.2 Oogenesis
3 Fertilization
3.1 The recognition of egg and sperm 3.2 The prevention of polyspermy 3.3 The activation of egg metabolism
In other instances (such as salamanders蝾螈 and mammals), the PGCs are specified by cell induction via neighboring cells. (The non cell-
autonomous manner)
Functionally conserved genes in Germ-Cell Development
Origin of the PGCs in mammals
There is no obvious germ plasm in mammals, and mammalian germ cells are not morphologically distinct during early development. Rather, germ cells are induced in gastrulating embryos In mice, the germ cells form at the posterior region of the epiblast, at the junction of the extraembryonic ectoderm, epiblast, primitive streak, and allantois (尿囊).
The mammalian PGCs appear to be induced in the early gastrulating embryos
The molecular mechanisms underlying the specification and determination of the PGCs in Mammals
So far, it has been reported that several maternal gene (at least 8 genes) are functionally necessary and sufficient for the pole plasm formation, and the germ cell specification/determination