invertebrate models Flashcards
what do sea urchins have
-large number of embryos, experimental manipulation
-transparent embryo which is large and easily accessible for manipulations
what do eugenic models entail of
-here breeding is easily done in a lab.
-Genes within the genome can be altered to study their effect on development.
- Caenorhabditis elegans/Drosophila melanogaster (fruit fly)
what are sea urchins
-Echinoderms (“spiny skin”)
-Echinoderms are Deuterostomes
-closer related to humans than we think
-PRIMITIVE protostome, the mouth is formed by gastrulation and the anus is formed secondarily- tinkered with in evolution however
whats the lifecycle of an animal like
-schematically
-4 hours it develops into a blastula through a number of stereotypic cell divisions
-they have a strict order and orientation
-From the first day onwards the embryo will undergo gastrulation movements, during which the primitive gut is formed, this fuses at the animal side forming a mouth (deuterostome), the larva has an internal calcareous skeleton that is responsible for these extensions on the pluteus larva
what are the two types of development Sea urchin experiments contributed to discussion on
-Mosaic or Regulative development.
-Weissman put forward the Mosaic model
-a variant of this is where cytoplasmic determinant control cell fate
-Alternative is Regulative development, differences can be generated de novo by cell-cell interaction
what does the mosaic model entail of
-the nucleus of the egg would contain determinants that specify different fates to different cells by specific segregation to these cells
how do sea urchins divide
-2 divisions at right angles along the Animal-Vegetal axis
-animal vegetal axis is an asymmetry in the egg that can already be observed at fertilization when the fertilised egg (zygote) is formed
-1 perpendicular to these divisions, separating the animal from the vegetal half
why is the development in sea urchin regulative and not mosaic
-when he separated the two blastomeres at the 2 cell stage he did not get 2 half embyos, rather he got two smaller but complete embyos, thus the cells had adapted their normal developmental programmes
sea urchin development : slight signs of mosaicism
-Splitting the 8 cell embryo in a ventral and dorsal half showed that there is at least along this axis a degree of mosaicism is present
-in this case, no embryo formed, rather an animalized and vegetalised incomplete larvae are the result, thus when we consider this axis there appears to be some form of mosaicism
what is meant by a gene model
-In “genetic model organisms” technologies have been developed to alter the genome of that organism.- In addition in such GENETIC MODELS have been chosen because they are relatively easy and quick to breed, thus one can do breeding quickly and efficiently and then examine the consequences of such gene alterations on development of the organism
what are the Ideal characteristics for ease of genetic analysis
-small organism (because of the need to keep large numbers) ✔︎
-large batches of embryos ✔︎
-short generation time ✔︎
-easy to breed ✔︎
-easy scoring of phenotypes +/-
-sequenced genome ✔︎
what are Caenorhabditis Elegans
-one of the most simplest organisms
-mainly consists of gut and reproductive organs
-has some muscle
-has neurons and sensory cells that convey information to the animal about the environment is navigating
life cycle of a C.Elegans
-develops really rapidly and hatches from the egg within 24 hours at normal temperatures
-The animal usually develops as a HERMAPHRODITE, it will first become male and then transform into a female that can use her own sperm to fertilise eggs
-Occasionally male only individuals occur,and these can mate with females. In this way continuous inbreeding, which would be detrimental for their fitness, is prevented
what is the first cleavage in C.Elegans like
-always asymmetric, this is due to the action of a set of Par proteins (Par from partitioning)
-the first cell division create a larger AB cell and a smaller P1 cell. The P1 cell divides to form the P2 and EMS cell whereas the AB cell forms ABp and Aba (A and P are anterior and posterior).
-very stereotypic cell division
what can happen to figure out the fat of early cells
-map them
what do each cells in C.Elegans make
-the AB cell mainly makes hypodermis
- neurons makes the EMS cell predominantly (but not perfectly) mesoderm and endoderm
- the C and D cells (formed from P2 and P3 resp.) will also make somatic tissues
- However P4 will go on and form the germ line.
-P4 receives a cytoplasmic granules named P-granules- required to make germ line
what do par genes act on
-our other invertebrate model Drosophila,but in another cellular context.
experiment that outlines why lineage invariation doesnt mean cell fate is determined
-the relative position of the cells is changed by simply prodding the the cells (changing position and therefore cells can adapt)
-this can lead to the ABa cell lying posterior and the Abp lying anterior
-These will then go on to produce the lineage according to their NEW position, this would be impossible if they would contain determinants. -The EMS cell is formed by what originally would have been the P2 cell, so also here there is no fixed determinant.
how many ells are formed during programming
-1090
-131 undergo destruction - apoptosis
what happens in programmed cell death (apoptosis)
-In multicellular organisms, cells are sometimes actively removed.
This happens during development but is also essential in a variety biological processes in adults.
-This is a highly controlled process, not a simple bursting of a cell (this is called NECROSIS).
-As apoptosis occurs in a highly stereotyped manner in C. Elegans development, it allowed an efficient genetic dissection of the process in this organism.
-In this organism the pathway/genes that are required for this process were first identified, using genetics and then molecularly.
why is apoptosis Essential for proper development
-Formation of reproductive organs Male/Female
-Skin between digits
-Immune system maturation
why is apoptosis Essential for Homeostasis
-Mitosis/Apoptosis to maintain constant number of cells
-Removal of damaged cells (DNA damage, Viral infections)
what diseases does improper regulation of apoptosis lead to
-Autoimmune disease
-Cancer
different genes identified in screening and what they are
-BID=BH3 interacting-domain death agonist
-Bcl2=B-cell lymphoma 2
-APAF1=Apoptotic protease activating factor 1
-Caspase=cysteine-aspartic proteases
-look at slide 29 to see these in mammals, drosophila and nematodes
