Animal Development Flashcards
4 stages of Animal Development
- Fertilization
- Cleavage
- Gastrulation
- Organogenesis
then growth!
Fertilization, Cleavage, Gastrulation, Organogenesis basics
Fertilization - egg and sperm fusion
cleavage - zygote subdividing and determinants partitioned in blastomere (body plan); cell division with no intermediate growth - fast division
gastrulation - germ layers
organogenesis - organs forming, cell interacting and differentiating
acrosome and mitochondria in sperm
acrosome: head of sperm; releases digestive enzymes that destroy the jelly layer/zona pellucida for sperm to reach egg
mitochondria: lots of mitochondria, need the energy to move to fertilize
jelly layer/zona pellucida in mammals
glycoproteins that release chemoattractants to guide sperm to eggs
yolk
nutrients to support growth of developing embryo
vitalline envelope
separates the egg from zona pellucida/jelly layer; outside of cell’s plasma membrane
cortical granules
vesicles that hold enzymes that will degrade the proteins that hold the vitalline envelope around the plasma membrane when fertilization occurs
Events in Fertilization (8)
- sperm binds to jelly layer
- initates acrosome reaction - chewing up jelly layer
- allows sperm-egg membrane fusion (bindin on sperm and bindin receptors n eggs)
- membrane fusion leads to egg membrane depolarization as a fast block to stop further fusion of sperms
- depolarization induces Ca2+ wave (triggers formation of fertilization envelope)
- induces cortical reaction
7.degrades bindin receptors and bindin proteins on sperm and causes vitelline membrane to lift and form fertilization envelope (slow block) - egg activation - egg recognizes fertilizaation has occured - DNA fusion of eggs? and intiates development
cleavage cell division
the whole embryo stays the same size, individual cells are getting smaller because its dividing
cleavage results in
blastomeres (the actual small cells, mass of cells)
–blastula: when cleavage is completed; embryo of 100+ blastumeres - a spherical layer of blasteomeres considered to be the first embryonic tissue (below)
blastoderm (first tissue) - surrounds a fluid-filled, yolk-filled (below)
blastocoel (first cavity)
establishment of body axes (first division in protostomes and much later in clceavafe for deuterosomes)
blastocyst
mammalian blastula; unlike other animals, it has an inner cell mass and outer cell layer (trophoblast) – inner cell mass becomes the embryo and trophoblast will form the embryonic portion of placenta
intrinsic vs extrinsic factors in cell specialization
intrinsic - lineage info, inherited from mother cell, present in the cytoplasm of mother cell and therefore cytoplasm of daughter cell: asymettric distribution of these fate-determinant cytoplasmic determinants can have daughter cells with different identities
extrinsic: induction, info from surrounding environment and neighboring cells
body axes
all animals except sponges
lateral-medial (left-right)
dorsal-ventral (back-belly)
anterior-posterior (head and feet)
cytoplasmic determinants
mostly protosomes/invertebrates
insects - Drosophila embryo!; assymetric distribution after first cleavage - resulting cells have different instrinsic information and different cell fates - highest concentration of bicoid in Drosophila mean head with the lowest becomes the tail/posterior SO future cell identity is set after very first cleavage division
-not mammals!
yolk polarity
animals like amphibians, reptiles, birds, fish
-asymmetrical distribution of yolk due to heaviness of yolk - in animals with large amounts of yolk
- region with less yolk becomes head while with the most becomes posterior
by the time the first cleavage comes - already established (left and right)
ventral and dorsal established where sperm entry
mammals body plans
uses induction and extrinsic information bc we have less yolk and no cytoplasmic determinants
splitting an egg after fertilization
with mammals - get identical twins!
with cytoplasmic determinants/yolk polarity: dividing too early due to the cytoplasmic determinants or yolk polarity - you get different cell fates and embryo fates!!
morphogenesis
gastrulation + organogenesis - resulting in organism’s shape and body organization
gastrulation results in
gut formation: archenteron (embryonic gut)
embryonic germ layers
APPEARANCE of major body axes - actually becomes visible
germ layers - embryonic tissues
endoderm
ectoderm
mesoderm
later differentiate into different tissues and organ systems
blastopore
invagination: group of cells move into blastocoel to form the endoderm
mesoderm
group of cells that move into the locations between the endo and ectoderm
archenteron
endodermal cells continue through interior of embry until it reaches the other side and creates a continuous tract or embryonic gut
fate of blastopores in deuterostomes and protostomes
protosomes mouths
deutersomes anus
diploplasts vs triploplasts
2 germ layers - radial symmetry and less tissue types vs 3 germ layers
germ layers in relation to tissues
ectoderm - nervous system and epidermis
mesoderm - muscle cells and connective tissue
endoderm - columnar cells in digestive system and internal organs
four extra-embryonic membranes from amniotes
germ tissues extend beyond embryo and develop into these
amnion, yolk sac, chorion, allantois
amnion
membrane surrounding fluid-filled cavity to give an aqueous environment and cushions against mechanical shock;
ectoderm
yolk sac
provides nutrients and blood vessels for transporting nutrients from yolk to embryo;
endoderm
chorion
gas exchange between embryo and air;
mesoderm
allantois
waste disposal and helps chorion with gas exchange;
endoderm?
extraembryonic membranes in placental mammals
yolk sac and allantois function as part of umbilical cord
placenta - provides oxygen and nutrients to a growing baby and removes waste product
development in placental animals
fertilization occurs in fallopian tube/oviducts; cleavage occurs while traveling through tube; implantation on uterine wall and gastrulation occurs after implantation
organs and tissues
organs made up of 2 or more tissues
tissues: groups of similar cells that work together on specific task
4 primary types of adult tissues
cells of germ layers will proliferate, migrate, and differentiate into :
epithelial tissue
connective tiissue
muscle tissue
nervous tissue
epithelial tissues
tightly packed sheets that cover surfaces and form barriers
polarized: top and bottom side
muscle tissues
contractile tissues that allow movements
connective tissues
cells in a extracellular matrix of plasmawith solids, jelly, liquids: adipose tissue (bodyfat),bone cartilage, blood, etc; support and connect other tissues - supports organs and blood vessels - links epithelial tissues to muscles; connecting bones to nuscles
nervous tissues
sensory and processing cells that transduce electrical signals or support cells that do
neurons and glia cells
skeletal, cardiac, and smooth muscle
skeletal is attached to bones and voluntary; cardiac line walls of heart and are involuntary; smooth muscle are walls of blood vessels, digestive tract, uterus, bladder, and other internal structures also involuntary
what systems do ectoderm form
nervous system, cornea and lens of eyes, epidermis of skin, epithelial lining of mouth and rectum
what systems do mesoderm form
skeletal, circulatory, lymphatic, muscular, excretory, reproductive, dermis of skin, lining of body cavity
endoderm derived systems
epithelial lining of digestive tract, respiratory, reproductive, urinary tract - liver, pancreas, parathyroids, thymus?
5 essential developmental processes
- proliferation
- programmed cell death
- cell movement and differential expansion
- differentiation - cell type specific changes in gene expression
- induction - cell cell communication which mediates basically all other developmental processes
epigenetics
how cell differentiation occurs - differences in cell types are result of expression of different genes even tho all cells share the same genome
cell differentiation - asymmetry
- during cleavage divisions, embryonic cells become different from one another if egg contains cytoplasmic determinants - cytoplasm is heterogenous (not uniform)
- after cell asymmetries are set up, interactions among embryonic cells can influence fate and change gene expression: induction!
example of organogenesis: formation of the nervous system
notocord forms: signals the ectoderm to fold (thicken and move to become) into a neural tube which becomes the spinal cord and brain while the notochord will disappear and become spongy discs in the vertebrae
somites
from the mesoderm; lies on either side of the vertebrate neural tube; temporary structures
later development: migrate to different parts of the body to develop into bone, skeletal muscle, and connective tissue; specific pattern of induction from nearby tissues from ectodern, neural tube, notochord. surrounding mesoderm –> determines what tissue a particular region a somite will become
morphogenesis
differential gene expression
morphogens and cytoplasmic determinants with regulatory genes
in a concentration gradient of drosophila embryos - cytoplasmic determinants that establishes anterior-posterior gradient?
cytoplasmic determinants are often regulatory genes? that direct expression of other genes - developmental “cascade” leading to proper development of animal
regulatory genes
regulatory genes that organize cells into groups along segments; which regulate genes that organize cells into individual segments, which regulate genes that establish anterior-posterior in each segment which triggers the Hox genes which trigger the development of structures which effect the effector genes (cell death, movement, differentiation)
Homeobox or Hox genes
type of regulatory genes; regulate gene expression by binding to DNA control regions like promoters and enhancers
encode transcription factors
-family of genes responsible for determining general body plan like number of body segments – each body segment is specificed by a specific comibation of Hox genes (segment identity!!) where other different body parts then develop
-all animals except sponges have this
-plants relu on Mads box (not evolutionary related)
-control identity of body parts “head architects” - have other lower tier genes for more specific instructions
transcription factors
if transcription factors attach to regulatory element: go for the transcription of that set of genome? so Hox genes make those transcription factors
misexpression hox genes
segments can take on new identities
misexpression of Ubx - lead to extra wings
of Antp: legs in new places - in segments its not supposed to be
Hox genes in tetrapods and in segment identity
for tetrapods with forelimbs, certain combinations of hox genes will lead to different body parts compared to just one hox gene by itself
duplication of Hox cluster
occurred in more than 2x in vertebrates during animal evolution - more genes mean more complex body types
Hox genes homology
homologous in animal kingdom, genetic sequences and positions on chromosomes are remarably similar across most animals
instructions of hox genes
“make something here” not HOW – passes the instruction to other regulatory genes which then make that animal’s version of that body part
