Determination Flashcards
what is determination? what is a cell’s potency during determination?
determination = second stage of commitment
determinated state is attained when cell/region carrious out its intended fate even after ectopic transplantation
cell is determined when its potency = its fate
what is clonal restriction, how does it relate to determination?
clonal restriction - using lineage mapping to determine fate of specific founder cells
if a founder cell crosses boundaries of structures across clones, it cannot be said to be determined to contribute to one structure at that stage
lack of clonal restriction can be a negative criterion
clonal restriction itself usually cannot be used as evidence unless sample size is very large - clones are likely exposed to different environments than real embryos and thus clonal restriction may not be representative of all embryos everywhere.
real life examples - what did clone analysis of Drosophila reveal?
clonal analaysis of dros. @ cellular blastoderm stage resulted in reproducible appearance of clones that overlapped between wings + legs on same side of body
therefore, clones overlapped w/ dorsal and ventral structures
what else did clonal analysis reveal about interactions (e.g. w/ mesothorax)? what did these observations hint at?
no clones were found to overlap between mesothorax region and head or abdomen.
these observations started to hint at (what we now know is true) that blastoderm cells are determined to contribute to a single segment, but are not yet determined to form certain structures along dorsal-ventral axis w/in that segment.
when are cells determined for a single segment?
at the blastoderm stage, not before!
define the community effect
tendency of large numbers of cells that are either isolated or ectopically transplanted to adhere to their original fate, whereas the same cells would tend to depart from their fate if treated as individuals
what causes the community effect and stabilization of fates?
autocrine signaling - signaling in which a cell secretes signal molecules that act on itself and/or on other cells of the same type
stabilizes determined state for a group of cells that are similary specified (or “biased”) based upon cytoplasmic determinants they have already inherited
give an example of the community effect
FGF (fibroblast growth factor) secretion + perception by mesoderm precursor cells in Xenopus blastulas are both required for maintenance of mesodermal fate.
what is another method for studying determination? give an example
creation of chimeras - organisms composed of cells w/ different genotypes
two 8 cell embryos can be fused into a single large blastocyst, which, when implanted into surrogate mother, will form into single mouse
define paracrine signaling and juxtacrine signaling
paracrine signaling - signaling of one cell to cells further away from it and of different type through the secretion of signal molecules
juxtacrine signaling - signaling between two adjacent cells in which both the ligand and receptors are membrane bound (are not secreted extracellularly like autocrine/paracrine).
