Samenvatting – Hoofdstuk 1 – EZO-22306
1.1.1
Before oogenesis begins – oogonium divides - 15 nurse cells and 1 oocyte precursor (at posterior
site of the egg chamber) are formed.
Anterior-posterior polarity in oocyte
Gurken - synthesized by nurse cells – transported to oocyte nucleus – translated to Gurken
protein – oocyte nucleus is very near posterior end of egg chamber – Gurken signal received
by follicle cells through torpedo gene (receptor protein) results in posteriorization of
follicle cells. following Par-1 protein (at posterior site oocyte) organises microtubules
(grow from ant. To post.).
PAR proteins are initially uniformly distributed in cytoplasm, but become concentrated in
posterior pole of oocyte.
Oskar – translated at posterior site
- recruits more par-1 protein
So microtubular rearrangement + increase in oocyte volume
increase in oocyte volume transfer of bicoid mRNA’s + nanos from nurse cells.
Dorsal-ventral Patterning in oocyte
nucleus moves anteriorly – determines dorsal position
Gurken signal has short diffusibility, only the dorsal follicle cells receive signal – dorsal morphology –
inhibits synthesis of pipe protein- pipe protein only made by ventral follicle cells.
Pipe activates Nudel protein – Nudel acgivates proteases – are products of gastrulation defective etc.
cascade reactions results in cleaved Spätzle protein, binding to Toll receptor – ventralizes cell.
1.1.2
Dorsal, the ventral morphogen
Dorsal gene – placed in oocyte by nurse cells
- when translated – found throughout the embryo
- translocated into nuclei in ventral part embryo - acts as transcription factor
- if Dorsal does not enter nucleus – the genes and all cells become dorsal cells
- in mutants in which all cells have ventral phenotype, Dorsal is found in every nucleus
Establishing a nuclear Dorsal Gradient
Dorsal produced – complexed with Cactus in cytoplasm syncytial blastoderm – if Cactus bound to it
Dorsal remains in cytoplasm – separation of Dorsal from Cactus is initiated Toll receptor – Toll is
activated by Spätzle protein, that is highest in ventral region, so Dorsal translocation also in ventral
cells – highest concentration Dorsal in ventral cell nuclei.
Effects Dorsal protein gradient
Dorsal protein specifies cells to become mesoderm in 2 ways:
1. The protein activated genes that create mesodermal phenotype
target genes: twist, snail, fgf8, fgf8 receptor, rhomboid
Twist: activates mesodermal gene, Snail: represses mesodermal genes, Rhomboid and fgf8:
activated by Dorsal, but repressed by snail and are not expressed in most ventral cells, but expressed
1.1.1
Before oogenesis begins – oogonium divides - 15 nurse cells and 1 oocyte precursor (at posterior
site of the egg chamber) are formed.
Anterior-posterior polarity in oocyte
Gurken - synthesized by nurse cells – transported to oocyte nucleus – translated to Gurken
protein – oocyte nucleus is very near posterior end of egg chamber – Gurken signal received
by follicle cells through torpedo gene (receptor protein) results in posteriorization of
follicle cells. following Par-1 protein (at posterior site oocyte) organises microtubules
(grow from ant. To post.).
PAR proteins are initially uniformly distributed in cytoplasm, but become concentrated in
posterior pole of oocyte.
Oskar – translated at posterior site
- recruits more par-1 protein
So microtubular rearrangement + increase in oocyte volume
increase in oocyte volume transfer of bicoid mRNA’s + nanos from nurse cells.
Dorsal-ventral Patterning in oocyte
nucleus moves anteriorly – determines dorsal position
Gurken signal has short diffusibility, only the dorsal follicle cells receive signal – dorsal morphology –
inhibits synthesis of pipe protein- pipe protein only made by ventral follicle cells.
Pipe activates Nudel protein – Nudel acgivates proteases – are products of gastrulation defective etc.
cascade reactions results in cleaved Spätzle protein, binding to Toll receptor – ventralizes cell.
1.1.2
Dorsal, the ventral morphogen
Dorsal gene – placed in oocyte by nurse cells
- when translated – found throughout the embryo
- translocated into nuclei in ventral part embryo - acts as transcription factor
- if Dorsal does not enter nucleus – the genes and all cells become dorsal cells
- in mutants in which all cells have ventral phenotype, Dorsal is found in every nucleus
Establishing a nuclear Dorsal Gradient
Dorsal produced – complexed with Cactus in cytoplasm syncytial blastoderm – if Cactus bound to it
Dorsal remains in cytoplasm – separation of Dorsal from Cactus is initiated Toll receptor – Toll is
activated by Spätzle protein, that is highest in ventral region, so Dorsal translocation also in ventral
cells – highest concentration Dorsal in ventral cell nuclei.
Effects Dorsal protein gradient
Dorsal protein specifies cells to become mesoderm in 2 ways:
1. The protein activated genes that create mesodermal phenotype
target genes: twist, snail, fgf8, fgf8 receptor, rhomboid
Twist: activates mesodermal gene, Snail: represses mesodermal genes, Rhomboid and fgf8:
activated by Dorsal, but repressed by snail and are not expressed in most ventral cells, but expressed
