Chapter 2: Specifying Identity Flashcards
the fate of a tissue is ___ when it is capable of differentiating autonomously when placed in a neutral environment. However, the cell fate is still capable of being altered if transplanted to a new environment with new neighbors
the fate of a tissue is specified.
3 types of specification
1) autonomous
2) conditional
3) syncytial specification
a cell is ____ when it is capable of differentiating autonomously even when it is placed into a new environment with a new neighbor
a cell is determine when it cannot be influence by the environment anymore. the commitment is nor irreversible.
a cell is considered differentiated when the cell:
stops dividing and develops specialized structures and functions.
egg cytoplasm is not homogenous. Different egg regions contain different ___ ___ that will influence the cell’s development
dif egg regions contain dif MORPHOGENETIC DETERMINANTS that will influence the cell’s development.
What is autonomous specification
factors that are in place in the cell very early allow the cells to know their fate without influence of other cells. Ie, they are being specified autonomously.
- each blastomere will form its determined cell type even when separted from the remainder of the embryo beacuse it already holds the factors it needs to create a specific cell type.
Explain autonomous specification seen in sea squirts.
muscle forming cells contain macho transcription factors that are required for muscle development. Only found in cells that will differentiate into muscle cells. Macho TF probably found in mesoderm cells allows these cells to differentiate into muscle cells, even if they are removed and placed in a petri dish away from the rest of the embryo.
What is conditional specification
process by which cells determinate and achieve their respective fates by interacting with other cells. Specified by array of interactions it has with its neighbors ex/ Juxtacrine, paracine, mechanical signalling.
In conditional specification, cell rearrangements and ____ may accompany it
cell migrations accompany specification. In autonomous specification however, the cells are specified by what they contain, and autonomous specification precedes any large-scale embryonic cell migration.
in conditional specification, interations ___ cells determine cell fates rather than being determined by ___ ___ particular to a specific cell type
in conditional specification, interactions BEWEEN cells determine cell fates rather than being determined by CYTOPLASMIC FACTORS particular to a specific cell type
- this results in the ability for cells to take on the fate of the cells in the region it gets transplanted in.
conditional specification in the sea urchin embryo
if you separate blastomeres from a 2cell/4cell/8 cell embryo, each isolated blastomere will produce a new complete organism. If it was autonomously specified and you separated each cell into nutral environments, it wouldve just created the tissue that the transcription factor inside them indicated. BUT in this case, a cells fate depends on that of its neighbors.
recombination experiments have shown that conditional differentiation/specification allws different cells to adopt different roles when displaced.
syncytial specification involves____cells
multinucleated cells in a single cytoplasm.
- during cleavage stages of insects, nuclei divide through 13 cycles without cytoplasmic cleavege. Forms an embryo called syncytial blastoderm.
in drosophila, nuclei replication without cleavage results in ___ ___> Within this structure, the identity of future cells is established ____ across the entire embryo, along the ___ ____ axis of the blastoderm.
in drosophila, nuclei replication without cleavage results in SYNCYTIAL BLASTODERM. Within this structure, the identity of future cells is established SIMULTANEOUSLY across the entire embryo, along the ANTERIOR-POSTERIOR axis of the blastoderm.
- THEREFORE, IDENTITY of each nuclei is established using gradients without any membranes separating nuclei into individual cells. Syncytial specification is like a combo of autonomous and conditional specification.
- as nuclei undergo waves of division, each nucleus positioned at specific corrdinates along the anterior posterior axis experiences unique concentrations of determination factors
- cellularization occurs just before gastrulation, after mitotic cycle 13, but cells determined to become the head, thorax and tail are specified before cellularization using syncytial specification via factor gradients,
In syncytial blastoderm, how do cells stay in the same position relative to the axial concentration gradient?
nuclei maintain their position in the syn. blastoderm with their own cytoskeletal machinery: their centrosome, affiliated microtubules, actin filaments, and interacting proteins.
In syncytial blastoderm, each nuclei radiates ___ ___ extensions from their ___ that establish an exert a force on other nuclei, ensuring regular spacing of nuclei across the syncytial blastoderm, ensuring that each nucleus is exposed to a specific factor gradient.
In syncytial blastoderm, each nuclei radiates DYNAMIC MICROTUBULE extensions from their CENTROSOME that establish an exert a force on other nuclei, ensuring regular spacing of nuclei across the syncytial blastoderm, ensuring that each nucleus is exposed to a specific factor gradient.
