Chapter 2 Developmental Patterning

Developmental patterning

cell speciation

how embryonic cells acquire trajectory toward certain cells

embryos of different organisms used different ways for cell fate

differentiation

cell committed to cell fate single cell forms many cells with specialized function

Differentiation divided into 2 stages

labile speciation and determination

Labile speciation

cell fate specified if it is capable of differentiating autonomously when in neutral environment

commitment of cells can be REVERSED

Determined cell

cell is capable of differentiating autonomously even when placed into another region of embryo commitment of cell CANNOT BE REVERSED

Modes of Commitment mechanism

autonomous specification, conditional specification, syncytial specification

Autonomous

cells know very early what it is to become without interacting with other cells

ex. blastomeres contain regulatory factors

fixed development

cell is removed and placed somewhere different, it will still develop into what it is supposed to.

title mosaic

independent, self-differentiating parts

Cytoplasmic determinants

lineage tracing and fate maps

lineage tracing

Tracks the development of cell maturation over time

ex. group of embryonic cells can be labeled to see what they become in adult organisms

fate maps Edwin Conklin

observations of tunicates (sea squirt) embryo sea speciation in tunicates

Dark yellow coloration that was asymmetrically partitioned within egg cytoplasm

called YELLOW CRESCENT to muscle cell in larva

Conditional speciation

fate of cells depends on the condition the cell finds itself in

interaction with neighboring cells

each cell has the ability to become any of many different cells

ex. blastomere removed - remaining cells alter their fate to compensate for missing roles

regulative development Driesch

Cell fates altered by abutting neighboring cells

ex. isolated sea urchin blastomeres by shaking them and produced complete, bilaterally symmetrical larvae

ex. identical twins

Hans Driesch Hypothesis

concluded fate of a nucleus depended solely on its location in embryo

Syncytial specification

interaction occurs between different parts of some cells

this happens through splitting (division) of the nuclei within the cytoplasm of the egg

syncytium

cytoplasm with many nuclei division of nuclei (many nuclei)

ex. insects use this to commit cells to their fate

Morphogens

The proteins responsible for providing positional information across anatomical axes (like dorsal-ventral or anterior-posterior) through concentration gradients

Morphogens concentration gradient

Diffuses from high concentration to low concentration over a long distance

-point of synthesis High concentration

Drosophila (fruit fly) anterior

produces protein bicoid diffuses toward posterior

*bicoid protein controls development of the anterior structures

Drosophila (fruit fly) posterior

produces protein nanos diffuses toward anterior

Drosophila (fruit fly) posterior and anterior forms

opposing gradients and coordinates system based on ratios

ex. regions distinguished by 2 proteins