Chapter 10: Sea Urchin Development Flashcards
What type of cleavage do sea urchin embryos undergo
radial holoblastic cleavage: occurs in eggs with sparse yolk, and it goes through the entire egg.
Outline the first 7 cleavages
1) first and 2nd cleavages are meridional and perpendicular to each other, going through both the animal and vegetal poles. (4 cells)
2) third cleavage is equitorial, separating the animal adn vegetal poles. (8 cells)
3) fouth cleavage: the 4 cells in the animal pole divide MERIDIONALLY (8 ANIMAL MESOMERE CELLS). The 4 cells in the vegetal hemisphere divide equatorially into 4 MACROMERES AND 4 MICROMERES . (16)
4) fifth cleavage: the 8 animal mesomeres divide EQUATORIALLY to form two tiers of animal cells, named An1, and An2. The 4 vegetal macromeres divide MERIDIONALLY to form 1 tier of 8 equal sized cells below An2. the 4 micromeres do not divide until either. This forms a tier with 4 larger micromeres and 4 smaller micromeres at the vegetal pole. The small micromeres divide one more time and then stop dividing until the larval stage of development.
5) 6th cleavage involves animal cells dividing meridionally and the macromere vegetal cells divide equitorially to form veg 1 and veg2 tiers (in addition to the 4 smaller micromeres that do not divide)
6) the 7th is the reverse of the sixth, and forms a blastula: cells will form hollow sphere surrounding a central cavity called a blastocoel
fifth cleavage: the 8 animal mesomeres divide ____ to form two tiers of animal cells, named___ and ___ . The 4 vegetal macromeres divide ____ to form 1 tier of 8 equal sized cells below An2. the 4 vegetal micromeres do not divide until either.
fifth cleavage: the 8 animal mesomeres divide EQUATORIALLY to form two tiers of animal cells, named An1, and An2. The 4 vegetal macromeres divide MERIDIONALLY to form 1 tier of 8 equal sized cells below An2. the 4 micromeres do not divide until either.
every cell in a blastula is the same sized, being connected by ___ ___ and contacts the outer ___ layer.
every cell in a blastula is the same sized, being connected by TIGHT JUNCTION and contacts the outer HYALINE layer.
In early blastula stages, how does it stay in a single layer?
there is an influx of protein-containing water into blastocoele, and its contact with they hyaline layer maintain a single cell layer of the blastocoele. As the cells continue to divide, the blastula remains one cell layer thick, thinning out as it expands.
after the 9th or 10th cleavage, the blastula cells have already been specified. How is blastula basal and apical polarity established? What does this allow?
the cells of the blastula become ciliated on the surface that faces AWAY from the blastocoele cavity. The ciliated blastula now has basal and apical polarity, and the cilia allows the lbasula to rotate within the fertilization envelope.
Once the blastula gets ciliated and is able to rotate, what happens to the cells of the vegetal and animal poles?
at the vegetal poles, cells thicken to form a VEGETAL PLATE.
at the animal hemisphere, the cells secrete a HATCHING ENZYME that digest the fertilization envelope. This allows the ciliated embryo to become a free swimming hatched blastula.
By the 60 cell stage, most embryonic cell fates are specified, but the cells are not irreversibly committed. What does the animal hald of the embryo give rise to? Veg1? Veg2? upper macromere tier? lower micromere tier?
animal half of the embryo gives rise to the ectoderm: larval skin and its neurons
- veg1 layer produces cells that can enter into either the laraval ectoderm too, or the endodermal organs
veg 2 layer can form either the endoder, coeloM (internal mesodermal body wall) or non-skeletogenic mesenchyme (generates pigment cells, immunocytes and muscle cells)
upper tier of the micromeres forms skeletogenic mesenchyme (primary mesenchyme, which forms the larval skeleton)
Lower tier of micromeres forms the larval coelum, but they technically do not play a role in embryonic developmend– they will contriubte tot eh development of adult tissues during metamorphosis.
animal half of the embryo gives rise to the ___: larval skin and its neurons
- veg1 layer produces cells that can enter into either the laraval ____ too, or the ____ ____
veg 2 layer can form either the ____, ____,(internal mesodermal body wall) or ____ _____ (generates pigment cells, immunocytes and muscle cells)
upper tier of the micromeres forms ___ ____ (primary mesenchyme, which forms the ___ ____)
Lower tier of micromeres forms the larval coelum, but they technically do not play a role in embryonic development– they will contriubte to the development of ___ ___ during ____
animal half of the embryo gives rise to the ectoderm: larval skin and its neurons
- veg1 layer produces cells that can enter into either the laraval ectoderm too, or the endodermal organs
veg 2 layer can form either the endoderm, coeloM (internal mesodermal body wall) or non-skeletogenic mesenchyme (generates pigment cells, immunocytes and muscle cells)
upper tier of the micromeres forms skeletogenic mesenchyme (primary mesenchyme, which forms the larval skeleton)
Lower tier of micromeres forms the larval coelum, but they technically do not play a role in embryonic developmend– they will contriubte tot eh development of adult tissues during metamorphosis.
in the 16-cell embryo, the large micromeres specify ___ (they do not need external stimuli)
specify autonomously
in the 16-cell embryo, the large micromeres (upper tier of micromeres) specify autonomously because they have inherited ___ ___ in the ___ pole, which are portioned into the large micromeres during the 4th cleavage event.
in the 16-cell embryo, the large micromeres (upper tier of micromeres) specify autonomously because they have inherited MATERNAL DETERMINANTS in the VEGETAL pole, which are portioned into the large micromeres during the 4th cleavage event.
the larger micromeres (upper tier of micromeres) in the 16 cell embryo are autonomously to be the ___ ___, (skeletogenic mesenchyme)
the larger micromeres (upper tier of micromeres) in the 16 cell embryo are autonomously to be the LARVAL SKELETON, (skeletogenic mesenchyme).
- the autonomously specified large micromeres are now able to produce paracrine and juxtacrine factos that conditionally specify the fates of neighbors
the autonomously specified large micromeres are now able to produce paracrine and juxtacrine factos that conditionally specify the fates of neighbors.
These factors tell the cells above the large micromeres to become ___ (the endoderm and the secondary mesenchyme cells), and induces them to ____ into the embryo.
the autonomously specified large micromeres are now able to produce paracrine and juxtacrine factos that conditionally specify the fates of neighbors.
These factors tell the cells above the large micromeres (THE VEG2 TIER) to become ENDOMESODERM (the endoderm and the secondary mesenchyme cells) (AKA THE NON-SKELETOGENIC MESENCHYME THAT FORMS PIGMENT CELLS, IMMUNOCYTES, AND MUSCLE CELLS) , and induces them to INVAGINATE into the embryo.
the autonomously specified large micromeres will eventually leave the blastula epitherlium and enter the blastocoele and feel around using ___. They migrate to new locations along the blastocoele wall and idfferentiation into a ___ ___. These large micromeres are considered to be __ ___ cells. After producing paracrine and juxtacrine signals, the cells above the large micromeres (veg 2) become ____ and causes them to then invaginate into the embryo.
the autonomously specified large micromeres will eventually leave the blastula epitherlium and enter the blastocoele and feel around using FILOPODIA. They migrate to new locations along the blastocoele wall and idfferentiation into a LARVAL SKELETON. These large micromeres are considered to be SKELETOGENIC/PRIMARY MESENCHYME cells. After producing paracrine and juxtacrine signals, the cells above the large micromeres (veg 2) become SECONDARY MESENCHYME AND ENDOMESODERM, and causes them to then invaginate into the embryo.
what is a gene regulatory network
interconnections among cell types to specify genes.
Double negative gate for skeletogenic mesechymal (large micromere) specification:
usually, Hesc represses ____< ___ ,__ and___ genes in every other non-micromere cell. These genes are involved in skeletogenic mesenchymal specification and are thus expressed in the micromeres via GESC suppression through Pmar1 activation due to Otx/betacatenin activation.
usually, Hesc represses alx1, ets, tbr, and delta genes in every other non-micromere cell. These genes are involved in skeletogenic mesenchymal specification and are thus expressed in the micromeres via GESC suppression through Pmar1 activation due to Otx/betacatenin activation.
alx1, ets, tbr, and delta (juxtacrine– can interact with other cells by delta on the membrane) activation due to PMAr1 repression of Hesc repressor = TF production = activation of other genes invovled in skeletogenesis.
