6

1. cells stop this (x) and start this (y)

   Anmerkungen:

   • x: dividing y: start developing specialized element and distinct functions
2. the generation of -

   Anmerkungen:

   • specialized cell type

Anmerkungen:

• the process that determines the cell to be a certain fate

1. stage 1: specification

   Anmerkungen:

   • the cell/tissue has a specific fate it will become, but this differentiation pathway is labile (can change) and reversible. there's no garauntee 
   1. capable of differienting autonomously when placed in a neutral environment
2. stage 2: determination

   Anmerkungen:

   • the cell/tissue has a certain fate and it is 100% DETERMINED to become that. non-reversible. happens very early on in embryonic development
   1. capable of differitiating autonomously even if placed into a non-neutral environment
3. 3 strategies of commitment

   Anmerkungen:

   • ACS
   1. conditional specification
      1. cell fate determined by the conditions surrounding the cell
      2. cells have ability to achieve their fate through a number of different interactions
         1. juxtacrine factors

            Anmerkungen:

            • cell-to-cell contact. cells must be close
         2. paracrine factors

            Anmerkungen:

            • secreted signals
         3. mechanical stress

            Anmerkungen:

            • physical properties of its local environment 
      3. predominates in most vertebrates like zebrafish or mouse; predomanites some invertebrates
      4. ex: normal back cells in blastula
         1. if normal development (no transportation)

            Anmerkungen:

            • cells form back tissue
         2. if transported to belly area

            Anmerkungen:

            • form belly
         3. if removed by glass needle

            Anmerkungen:

            • - -also considered normal development because no transportation
   2. syncytial specification

      Anmerkungen:

      • Specification of presumptive cells within such a common cytoplasm containing many nuclei.  
      1. what is a synctium?

         Anmerkungen:

         • a cytoplasm containing many nuclei
      2. uses elements from both autonomous and conditional specification
      3. predominantely in insects like drosophilia
      4. cell fate OF BODY REGIONS determined by conditions affecting nuclei in a single multinucleate cell
         1. specification of body regions by interactions between cytoplasmic regions BEFORE cellularization of the blastoderm
      5. a cytoplasm with many nuclei
         1. nuclei divide through 13 cycles in the absence of any cytoplasmic cleavage
            1. cycles 1-9 are pre-blastoderm
               1. cycles 10-13 are synctial blastoderm cycles
                  1. next, cellularization interphase 14 then cellular blastoderm is
                     1. after cellularization, both autonomous and conditional specification are seen
                        1. check ppt slides for which part i missed
   3. autonomous specification
      1. cell fate determined before fertilization by morphogenetic factors in ovum regardless of their environment
         1. what are the morphogenetic factors?

            Anmerkungen:

            • mRNA or transcription factors
            1. example: the macho gene
               1. a transcription factor that regulates (x) in the tunicate

                  Anmerkungen:

                  • muscle development
               2. B4.1

                  Anmerkungen:

                  • this is the (part of the) blastomere where b4.1 is expressed
               3. slide 10
         2. blastomere inherits transcription factors from?

            Anmerkungen:

            • egg cytoplasm
         3. "regardless of their environment" ?

            Anmerkungen:

            • each blastomere will form most of its cell type even if separated from the rest of the embryo
      2. predominates in most invertabrates like tunicate
   4. no embryo uses only 1 type of specification
      1. embryos that use autonomous early use conditional for the formation of some organs
      2. syncytial can be used for very early events, both autonomous and conditional will occur later on

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