Chapter 2 - Specification

cell’s developmental fate is restricted, but the cell is not overly showing changes in structure, function, or biochemistry

what is commitment

1) specification

2) determination

2 stages of commitment

specification

1st stage of commitment and reversible → cell’s fate can still be altered

it will become the cell it was sought to be

if cell in specification phase of commitment is placed by itself what will occur

determination

2nd stage of commitment and irreversible → no matter what the environment, the cell will become what it’s set to be

differentiation

display of different phenotypes by cells of the same genotype

after commitment

does differentiation come before or after commitment

surround cell of interest with cells of a different fate

1) if the cell of interest still becomes its original cell fate then it’s in determination phase

2) if the cell of interest takes on the fate of the surrounding cells instead, then it’s in the specification phase

how to differentiate if cell is in specification or determination commitment phase

fate maps

how do we know what a cell is specified to be

differentiated cells

produces specialized proteins and has specialized functions

1) autonomous specification

2) conditional specification

3) syncytial specification

what are the 3 types of cell type specification

blastomeres of embryo are given a set of determination factors from the egg cytoplasm

what is autonomous specification

blastomere

cell at blastocyst stage

conditional specification

interactions with other cells determine cell fate

syncytial specification

only nuclei divide initially and gradients of that determine cell fate

syncytial specification

which cell type specification do insects typically use

yes!

can 1 organism have different cells use different type of cell type specification

through an isolation experiment → isolate the red cells, and if they become ciliated in isolation then it’s autonomous specification because it knew what to become without any other cells around

you have a presumptive trochoblast in which there are red and blue cells. the red cells become ciliated and the blue cells do not. how can we tell if this is autonomous specification?

it’s ciliated cells

what is a trochoblast

snail

what type of animal is Patella

muscle cells in the tail of the tunicate

what does the yellow crescent at the bottom of the tunicate cell become

the cells still became what we expected them to become (including the muscle cells of the tail)

during the 8-cell stage of the tunicate embryo, the cells underwent an isolation experiment → what was the result

macho mRNA (made into protein)

what mRNA in the oocyte regulates muscle development in tunicates

at the bottom where the yellow cytoplasm is and where the muscle cells end up developing

where is macho mRNA seen in the tunicate egg

muscle cells of the tail will only develop in that region

what does localization of macho mRNA at the bottom of the tunicate egg result in

used in situ hybridization to stain the specific mRNA to visualize it

how were we able to see where the macho mRNA was located in the tunicate egg

in the same area where macho mRNA was localized

when we stain for the muscle actin where is the staining showed in relation to macho mRNA

when macho was depleted, there was much fewer muscle cells

what did the lose it experiment showcase in the tunicates and muscle cells

when macho was added to other blastomeres, there were more muscle cells and in more places

what did the move it experiment showcase in the tunicates and muscle cells

there is no compensation

in autonomous specification, what happens if cells are killed off

transplant experiment → moving cells from one part of the body to another part

what type of experiments are used to prove conditional specification

those cells would now form belly tissue instead

in conditional specification, if normal back cells are transplanted to the belly region what occurs

other cells will compensate, so normal development will still occur

in condition specification, what happens if cells are removed

pluteus cells at the 4-cell stage were isolated, yet the cells were still able to develop into plutei → the cells compensated

what was Driesch’s experiment demonstrating conditional specification

syncytium

cytoplasm containing many nuclei

Drosophila melanogaster

which model organism experiences syncytial cells

the nuclei are in a specific position of each other due to microtubules keeping them spaced and preventing crowding

how are the nuclei in positioned during the interphase stage of nuclear cycle 13 of the fruit fly syncytium

factor that occurs in a concentration gradient and turns on different sets of gene at different concentrations

what is a morphogen

Bicoid is high in concentrations at the anterior end and low at the posterior end

Caudal is high in concentrations at the posterior end and low at the anterior end

what do the morphogens Bicoid and Caudal in the cytoplasm impact during syncytial specification in Drosophila

they activate specific nuclear genes depending on the concentration

what do morphogen gradients cause

1) have staged embryos at different developmental stages

2) dissociate those embryos into single cells for each developmental stage

3) every cell gets a different barcode which is placed on droplet with the cell to sequence

4) release RNA and generate cDNA (more stable) then sequence the DNA to determine what genes being expressed

5) conduct for lots of genes

5 steps of single-cell RNA sequencing (scRNAseq)

epiblast

developing embryo made up of stem cells

hours post fertilization

what does hpf stand for

how cells differentiate over time

what do developmental trees show