Dev. Bio

• Ectoderm: generates outer embryonic layer (skin, brain, nervous system)
• Mesoderm: middle region (blood, heart, kidney, gonads, bones, muscles)
• Endoderm: interior part of embreyo (digestive tube epithelium, associated organs)

• 1. General features develop first
• 2. More specialized are generated from general features
• 3. Embryo of advanced species doesnt go thru adult stage of lower species
• 4. Advanced species have common embryos as lower species but not common adult stages

• Homologous: similarity of structures in embryo coms from common ancestor
• Analogous: similarity comes from performance of the same function

• example: Wings vs. Arms
• Human arm, seal limb, bat wing, bird wing = homologus
• bat wing and bird wing = analogous (similar because they formed that function, not from winged ancestor)

• follow individual or groups of cells and document their divisions, migrations, differentiation, dealth
• allowed for 2 cell types to be found
• epithelial cells
• mesenchymal cells
• allowed for fate maps to be made (provide easy comparison between organisms)

• eptihelial: tightly connected to neighboring cells, in sheets or tubes, immobile
• mesenchymal: independent entities, migratory

• rapid, mitotic divisions
• increase cell number
• egg has same volume
• single cell called blastomere

dramatic changes in cell postitions to generate the three germ layers

ex. frog: small slit formed 180 degrees opposite of sperm entry-marks dorsal side (top) of embryo

• extensive cell-cell interactions resulting in tissues and organs
• signaling between tissues
• reciprical signaling: one thing signals something which signals something else

ex. frog: notochored (formed by mesodermal cells) signal ectoderm to not be epidermis, which form nervous system, which signals mesoderm next to notochord to become muscle

transition from larva to sexually mature adult

precursor to multicellular organisms

• somatic cells differentiated from germ cells
• asymmetrical division (due to gls binding to mitotic spindle)
• large cells: lag genes act, make gonidum
• small cells: regA genes act, make somatic cell, cell death
• asexual development
• 1. symmetrical divison (to make 32 cell embryo)
• 2. asymmetrical after that (inside out: gondial cell outside, somatic inside
• 3. embryo turns inside out
• inversion causes shape change
• microtubules and microtuble motor (kinesin) required for inversion
• sexual reproduction
• sex based on sexual inducer
• can survive dry environment, becomes asexual

• multicelluar organization
• cells come together and work

ex. all cells in slug could be alone, but they come together when food is scarce and work together to move. can produce spores which can survive bad conditions (eventually find food)

multicellular animals that pass thru embryonic stages of development

• protosomes: mouth formed first
• deuterostomes: anus formed first

• phenotypic differences due environmental change
• different forms called morphs

ex. temperature and sex of offspring

• autonomous: blastomeres act independently, each contributing fate to whole organism. morphogenetic determinates. mosaic model
• syncytial: many nuclei share common cytoplasm (cytoplasm not uniform), morphogen dictates different fates depending on the concentration gradient. ex. bicoid protein
• conditional: extensive cell-cell interactions, piece removed develops more cell types/fates than when it was part of a whole, there were limitations, regulative development

morphogens tell positional information (what you develop into, not what organ you are)

ex. fly. taking piece of leg and putting it in the antenna. still leg, but much thinner because it is not located in the antenna.

• cells organize themselves in specific ways to give rise to organs and tissues
• use integral membrane proteins- cadherins
• like-binds-like, due to type and amount of expression

form adheren junctions (linked by actin, common in epithelia) and desmosomes (linked via intermediate filaments, common is mechanical stress cells)

• 5 extracellular domains with Ca between
• 1st EC provides specificity to bind
• intracellular bind to b-catenin in ER and maybe a-catenin
• unknown binds to actin filaments for structure

binds (4 models) with W (tryptophan)

• leading edge of cell that is extended in order to get in contact with other cells
• Arp 2/3 complex is linked with branched actin filaments which provides movement

• as cells move closer, cadherin interaction occurs
• a-catenin believed to be attached to b-catenin
• as more cadherins move together to form connection, a-catenin moves off, forms dimers, and interacts with actin filaments causing Arp 2/3 complex to be inhibitted
• this bundle of actin and a-catenin provides structural support

a-catenin sends signal when cells are connected

• migratory tumors (maligant) break away from orgin
• epithelial and mesenchymal transition mesenchymal

cadherin levels may play a role in cancer (less cell-cell binding = less cadherin = movement ()

genomes of somatic cells with in a multicellular organism are essentially the same

ex. cloning: removed somatic cell genome of donor and place in zygote of another animal (whose genome has been destroyed) = embryo forms offspring.

• every cell nucleus has complete genome
• only small % of total genome is expressed in each cell

• determining gene expression
• know what you are looking for

collect cells- lyse and seperate mRNA- use gel electrophoresis- transfer to nylon membrane- probe for specific mRNA

• gel electro: bigger on top, smaller on bottom
• probe: complementary sequence to mRNA

• determining gene expression
• how gene acts under different conditions (dont need much mRNA)

mRNA- perform reverse transcription to make cDNA- destroy mRNA- perform PCR with gene specific primers- quantitative amount of end product

determines how much mRNA is acting under different conditions

• determining gene expression
• using 2 different cell types (male vs female, cancer vs normal)

mRNA- reverse transcription- dye each sample different color- equal amounts of each hybridized- color scheme

• determining gene expression
• see where gene fucntions

uses probe labeled with detector to determine where phenotype shows

• transgenic animals: add gene into developing organism and determine the effect
• knock out or knock down: removed a gene, or mRNA, from developing organism and see effect

embryonic stem cell (has full potential to become mouse)- grow invitro- add cloned gene in a vector to cell- select cells which incorporated the gene and put in host embryo- inject embryo in fetus

mate chimeric mouse with norma (hope trangenic cells become germ line)l- get heterzygote offspring- mate heterzygote and hope for homozygote

take culture of embryonic stem cells- use restriction endonuclease to removed gene- reseal chromosome- continue thru duplication, transcription and translation- determine phenotype

select heterozygous ES cells- inject ES into blastocyte- inject blastocytes into uterus- formation of chimeric mice

ex. Cre/loxP and FLP/FRT

systems which rely on recombination to remove specific genes

clone sequences surround DNA of interest- sequences recognized by recombinase- removes DNA

• tissue specific
• grow ES that have gene flanked by loxP
• target gene expressed in all tissues where Cre is not expressed, delted in tissue where Cre is expressed

know protein, want to know function- knock down

• 1. start with mRNA sequence, single strand
• 2. pick short, unique sequence to the protein
• 3. make complementary sequence, now double stranded
• 4. put new double stranded mRNA in cells
• 5. cell machinery notices double strand, and pulls them apart
• 6. complementary strand binds to mRNA in the cell
• 7. the bound mRNA is chopped up since it is double stranded
• 8. Without the mRNA, the protein cannot be made

western blot shows RNA knock down

• allow to determine the expression pattern of a gene
• green fluorescent protein (GFP)

ex. paralyzed animals. add GFP to end of gene, inject good gene into animals with the mutant gene, some of the progeny are no longer paralyzed. use fluorescent microscope to see which cells are effected.