Summary Mechanisms of Development (MOB-20803)

Summary Mechanisms of Development
lecture 1 and 2
Multicellularity evolved at least three times in the course of the evolution (animals, plants and fungi)

All cells:
 store their hereditary information in the same linear chemical code (DNA)
 transcribe portions of their hereditary information into the same intermediary form (RNA)
 translate RNA code into protein code
 use proteins as catalysts
 control the activity of individual genes by regulatory proteins binding to DNA (‘transcription
factors’)

All eukaryotes:
 have a cytoskeleton
 have internal membranes (including a nuclear envelope)
 have mitochondria

Transcription factors are very important for the formation and the differentiation of all the cell in the
development of organisms

There are 4 essential processes that contribute to mechanisms of development
 cell proliferation  the making of more cells out of one
 cell specialization  a cell becomes a specific cell
 cell interaction  the specialized cell communicates what the other cells have to become
 cell movement  the movement of the specialized cells to their correct formation

Cell specification: differences in regulators that
initiate cell specialisation (the cell knows what
it has to become but you can see it yet)
Cell differentiation: changes in protein content
complete and lock cell specialisation
Pattern formation: the process that leads to a
spatial pattern of cell specification

DNA (all information)  transcription  RNA (active information)  translation Proteins (building
blocks) + transcription regulators  used or not-used

Conclusions:
 Multicellular development evolved several times
 Development is about making cells different at the right place and time
 Development is about how to use entangled information

Axis of animals:
 Anterior-posterior axis
 Dorsoventral axis
 Left-right axis

Axis of plants:
 Apical-basal axis
 Radial axis
 Bilateral axis


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, The axis are independent systems with limited interaction, if you change something in one axis
system then the others are (almost) unaffected

Animals Plants
Body plan almost ready in embryo Embryo + post-embryonic development
Cells change position in body to form layers Rigid cell wall and therefor no cell movement
Development less affected by environment Overall development highly controlled by
environment

Tissues are formed by precisely oriented cell divisions, but moved cells know their new position. If
you remove a single cell another cell with another function can fill its place and change its purpose 
continuous positional information

The main similarities in development between animals and plants are:
 Pattern formation by gene regulation programs
 Differences in gene expression (transcription and translation)  different cell types

The pattern formation is mostly due to differences in transcription between different cells, which is
guided by transcription factors. Therefore transcription factors guide pattern formation

Developmental biology and evolution:
 Development differs between species
 This is due to selected mutations
 Proteins are only partially flexible for evolutionary change
 Transcription factors therefore evolve slowly
 Many mutations that rapidly change development occur on DNA in TF binding sites, thus
influencing only one target gene

During first cell cycles, auxin maxima are formed at root and embryotic leaf (cotyledon) poles
Auxin can induce transcription factors, like PLETHORA, and this transcription factor can form a
gradient and through the transcription factors many target genes it can control where cells divide
and do not differentiate

Locally produced RNA  translation of PLT protein  divided over daughter cells  protein gradient

Auxin is a long range plant developmental signal which allows coordination of development
Auxin and PIN transport protein form polar flow, which is the regulated transport of auxin in plants

Summary:
 Plants develop most architecture after embryogenesis by using meristems
 Cells in plant meristems divide in meaningful orientations and know in which tissue they are
 Meristem cells sense environmental cues and adapt their development
 Plants use mobile long-distance signals to organize development
 Plants use transcription factors for pattern formation as animals do

Lecture 3
Syncytium: is a cell with multiple nuclei, after the cleavage
stage of the fertilized fruit fly egg. After the syncytium the
nuclei migrate to the periphery and form boundaries




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