6

6

1. differentiation

   • cells stop this (x) and start this (y)
     • x: dividing y: start developing specialized element and distinct functions
   • the generation of -
     • specialized cell type

2. commitment

   • the process that determines the cell to be a certain fate
   • stage 1: specification
     • the cell/tissue has a specific fate it will become, but this differentiation pathway is labile (can change) and reversible. there's no garauntee 
     • capable of differienting autonomously when placed in a neutral environment
   • stage 2: determination
     • the cell/tissue has a certain fate and it is 100% DETERMINED to become that. non-reversible. happens very early on in embryonic development
     • capable of differitiating autonomously even if placed into a non-neutral environment
   • 3 strategies of commitment
     • ACS
     • conditional specification
       • cell fate determined by the conditions surrounding the cell
       • cells have ability to achieve their fate through a number of different interactions
         • juxtacrine factors
           • cell-to-cell contact. cells must be close
         • paracrine factors
           • secreted signals
         • mechanical stress
           • physical properties of its local environment 
       • predominates in most vertebrates like zebrafish or mouse; predomanites some invertebrates
       • ex: normal back cells in blastula
         • if normal development (no transportation)
           • cells form back tissue
         • if transported to belly area
           • form belly
         • if removed by glass needle
           • - -also considered normal development because no transportation
     • syncytial specification
       • Specification of presumptive cells within such a common cytoplasm containing many nuclei.  
       • what is a synctium?
         • a cytoplasm containing many nuclei
       • uses elements from both autonomous and conditional specification
       • predominantely in insects like drosophilia
       • cell fate OF BODY REGIONS determined by conditions affecting nuclei in a single multinucleate cell
         • specification of body regions by interactions between cytoplasmic regions BEFORE cellularization of the blastoderm
       • a cytoplasm with many nuclei
         • nuclei divide through 13 cycles in the absence of any cytoplasmic cleavage
           • cycles 1-9 are pre-blastoderm
             • cycles 10-13 are synctial blastoderm cycles
               • next, cellularization interphase 14 then cellular blastoderm is
                 • after cellularization, both autonomous and conditional specification are seen
                   • check ppt slides for which part i missed
     • autonomous specification
       • cell fate determined before fertilization by morphogenetic factors in ovum regardless of their environment
         • what are the morphogenetic factors?
           • mRNA or transcription factors
           • example: the macho gene
             • a transcription factor that regulates (x) in the tunicate
               • muscle development
             • B4.1
               • this is the (part of the) blastomere where b4.1 is expressed
             • slide 10
         • blastomere inherits transcription factors from?
           • egg cytoplasm
         • "regardless of their environment" ?
           • each blastomere will form most of its cell type even if separated from the rest of the embryo
       • predominates in most invertabrates like tunicate
     • no embryo uses only 1 type of specification
       • embryos that use autonomous early use conditional for the formation of some organs
       • syncytial can be used for very early events, both autonomous and conditional will occur later on

3. experiments

   • weismann's germ plasm theory of inheritance
     • 1. each cell of embryo develops autonomously
       • 2. equal chromosomal contributions from sperm and egg
         • 3. chromosomes carried the inherited potential for this new organism
   • roux's attempt to demonstrate autonomous
     • He destroyed one cell of a 2-cell frog embryo that resulted in the development of only one half of the embryo
     • DEFECT
     • frog
   • driesch's demonstration of conditional
     • RECOMBINATION EXPERIMENT
       • explained?
     • sea urchin
     • 1st experimental evidence of conditional