Development Flashcards
define development
how genotype (DNA sequences) becomes phenotype (form and function of an organism )
what 2 protein coding genes control development and how
1) transcription factor genes —> determine cell’s function
2) intercellular signaling genes —> cellular communication
what portion of your protein-coding genes are dedicated to development?
24%
role of transcription factor genes
encode transcription factor proteins that determine which other genes are turned on or turned off in a cell
2 type of intercellular signaling genes
1) intercellular signaling ligand genes: encode secreted protein ligands that allow cells to talk to other cells
2) intercellular signaling receptor genes: encode cell surface receptor proteins that allow cells to listen to other cells
purpose of using hundreds of different intercellular signaling ligands and receptors
makes up a cellular “language” for cells to communicate position, cell cycle status, timing, differentiation status, etc. during development
how do cells respond to each other?
by changing the expression of genes, including transcription factors
4 stages of development
1) growth: more cells
2) morphogenesis: cells form shape
3) patterning: embryonic cells allocated
4) differentiation: cells function in the right places
describe stage 1 of development (growth)
1 cell becomes millions (or billions or trillions)
describe stage 2 of development (morphogenesis)
embryonic cells take on the basic shape of an organism
describe stage 3 of development (patterning)
embryonic cells in specific parts of the embryo are “fated” to form different tissues, organs, and structures
describe stage 4 of development (differentiation)
embryonic cells mature into fully functional cells, tissues, organs, structures
can the 4 stages of development can occur at the same time?
yes
at what rate do cells divide in early development? what about late development into adulthood?
in early development, most cells divide at a similar max rate
in later development, different cell types divide at different rates
why is it important for different cell types to divide at different rates?
allows tissues/organs to grow at different rates to achieve different sizes
what is a cell’s division rate determined by?
“cell cycle check point” proteins
what are cell cycle check point proteins regulated by during development?
intercellular signaling receptors & ligands and transcription factors
does the zygote (fertilized egg) have all the resource it needs to get through early development?
yes, they were loaded into the egg cell made by the female, but no change in size is possible without additional nutrients and energy
what are larvae? % of animals on Earth that have free-living larval forms?
larvae can feed themselves to keep developing, they are feeding embryos
80% of animals on Earth
how does morphogenesis create the form or shape of an organism?
via morphogenetic movements, which are the coordinated movements of embryonic cells to give shape
3 types of morphogenetic movements
invagination, migration, apoptosis
describe invagination, what is it driven by?
indenting of a sheet of cells forms a groove, tube, or cavity driven by changes in cells shape caused by changes in the cytoskeleton
describe migration, what is it caused by?
amoeba-like movement of cells to a new place caused by changing expression of cell adhesion and cytoskeletal genes
describe apoptosis and how it contributes to morphogenesis
apoptosis is programmed cell death and it contributes to morphogenesis be removing cells and “sculpting” the body
what controls morphogenetic movements of a cell and whether it goes through apoptosis? how?
intercellular signals and transcription factors, which regulate the expression of cytoskeletal, cell adhesion, and apoptosis genes/proteins
what is patterning?
sets of embryonic cells in specific parts of the embryo are allocated to form specific tissues, organs, and structures; cells are fated by gradually acquiring their set of unique transcription factor proteins
difference between axial patterning and tissue patterning
-axial patterning involves whole regions of the early embryo along the main body axes acquire specific T.F.s combos
-tissue patterning involves individual cells in embryonic regions progressively acquire their own unique set of T.F.s
what are the body axes along which axial patterning occurs?
dorsal-ventral, anterior-posterior, left-right
2 things driving axial patterning
1) maternal determinants
2) morphogen gradients
describe maternal determinants
proteins and RNAs that are anchored to particular parts of the cytoplasm in the fertilized egg (zygote) and they are positioned during egg production
examples of maternal determinants
1) transcription factors
2) intercellular signaling ligands/receptors
3) mRNAs encoding TFs, ligands, receptors
4) micro RNAs that target mRNAs encoding TFs, ligands, receptors
how do maternal determinants instantly create embryonic cells with different combos of T.F.s, ligands, and receptors with the initial first few cell divisions? without what???
because maternal determinants are localized to different parts of the zygote, cell division instantly creates embryonic cells with different combos of T.F.s, ligands, and receptors without any new transcription or translation
what adds to the contribution of maternal determinants to cause axial patterning?
cells must talk to each other (morphogen gradients) in order to pattern complex animals
describe morphogen gradients
concentration gradients of secreted intercellular signaling ligands that pattern the embryo
what are intercellular signaling ligands? purpose?
intercellular signaling ligands (or their mRNAs) are often maternal determinants (or are “turned on” by maternal determinant transcription factors) that are secreted by small clusters of cells and diffuse across the embryo between cells and are received by cells with the right receptors
what do different concentrations of ligands cause in the responding cells?
causes responding cells to express different kinds and amounts of transcription factors, “patterning” the responding cells
2 processes that drive tissue patterning
1) asymmetrical cell division
2) short-range intercellular signaling
describe asymmetrical cell division
transcriptions factors (or RNAs) are localized to certain parts of the cells, after division the daughter cells have different combos of T.F.s (similar to maternal determinants)
describe short-range intercellular signaling
(similar to morphogen gradients) signaling cell releases ligand, responding cell expresses different T.F.s
what is differentiation?
embryonic cells mature and take on their final form and function
role of transcription factors during differentiation?
T.F.s turn on hundreds of tissue-specific effector genes which allow a mature cell to do its job
epigenetic role of transcription factors during differentiation
T.F.s recruit different enzymes to genes that are on or off; these enzymes make epigenetic changes to histones that keep the right genes on and other genes off
epigenetic changes that turn genes on
his tone acetylation, euchromatin
epigenetic changes that turn genes off
DNA methylation, histone deacetylation, heterochromatin
6 main stages of vertebrate development
1) zygote: fertilized egg (diploid)
2) cleavage stage
3) blastula
4) gastrula
5) neurulation
6) organogenesis
describe the cleavage stage
repeated division of the zygote (growth, patterning)
describe the blastula stage
ball of cells becomes hollow (growth/cell division, patterning, morphogenesis)
describe the gastrula stage
the blastula invaginates to create two cell layers (growth, patterning, morphogenesis)
what is the outer layer of the gastrula? what does it differentiate into?
ectoderm, differentiates into skin and nervous system
what is the inner layer of the gastrula? what does it differentiate into?
mesoderm and endoderm, differentiates into everything else inside of the body
consequence of incomplete gastrulation?
gut can be partially outside of the body (laparochisis)
describe the neurulation stage
formation of the nervous system by rolling up of dorsal ectoderm into neural tube (growth, patterning, morphogenesis, differentiation begins)—> basic body plan formation is complete
consequence of failed neurulation
spina bifida in which the spinal cord is still open
what does neurulation require?
folic acid (vitamin B9), supplementation for pregnant women
describe the organogenesis stage
development of organs and other structures by coordinated growth, patterning, differentiation, morphogenesis
