developmental bio exam 3

acromsome, acrosomal vesicle

digest proteins and complex sugars

movement of sperm

flagellum made up of tubulin motorized by the axoneme (formed by microtubules coming from centrioloes at the based of the sperm nucleus)

Kartagener syndrome-primary ciliary dyskinesis (importance of dynein in sperm motility)

• characterized by defect in gene for dynein

• males are sterile - nonmobile sperm

• males and femalres are more prone to bronchial infections with immotile respiratory cilia

• cilia also important for left-right axis so patients have 50/50 chance of heart being on the right side of body

anatomy of egg INVERTEBRATES

vitelline envelope: ECM on outside that forms fibrous mat - important for species specific recognition/binding

anatomy of egg MAMMALS

Zona pellucida: extracellular envelope, separate from egg surface, thick ECM

cumulus: ovarian follicular cells - activiate sperm as nears egg

corona radiata: region between cumulus and zona pellucida

external fertilization in echinoderms (sea urchins, sand dollars, sea stars)

1. fusion of acrosomal vesicle with sperm cell membrane (exocytosis that results in release of contents of the vesicle)

2. extension of a cellular protrusion-acrosomal process

How does the acrosomal process bind the egg surface?

• in sea urchins - bindin protein 30,500 Da protein

• binds species specifically

roles of Bindin

• promote fusion

• sperm egg adhesion: ensures sperm attaches specifically to the egg

• species-specific recognition: faciliates recognition between egg and sperm of same species, preventing cross specific fertilization

2 mechanisms to block polyspermy in sea urchins

1. Fast Block - change in electrical potential of egg cell membrane

2. Slow Block - physical block exocyotsis of cortical granules

3. Goals - Eliminate sperm’s ability to fuse (after one has)

4. Push sperm already bound to outer membranes away

Slow Block

• Cortical granule reaction: slow block to polyspermy where sperm bound to the vitelline envelope are removed; many animal species; 1 min after fusion

Internal Fertilization in Mammals : Translocation of Gametes into the Oviduct

Translocation of sperm:

1. Sperm motility: thick protein sheaths of the axoneme, strong flagellar action to move through thick cervical mucus

2. Uterine muscle contractions

3. Sperm rheotaxis: migrate against the direction of the flow with sperm specific calcium channels to monitor direction of the current

These sperm are immature and NOT capable of finding or entering the egg, need to undergo capacitation and hyperactivation

capacitation

Maturation (gain of capacity) - occurs in oviducts

1. recognizing the cues that will guide them to the egg

2. undergoing the acrosome reaction

3. fusing with the egg cell membrane

hyperactivation

swim at greater speed and force

gamete fusion, sperm entry

• izumo: exposed after acrosomal reaction

• BINDS to: Juno - oocyte membrane protein

• all mitochondria are derived from mother

Early cleavages occur independent of nuclear material

Cleavages do not require DNA - mom provides everything

Evolutionary history of gastrulation

• Ernst Haeckel, came up with Gastraea Theory (“primitive-gut animal”), ancestral invagination mechansim to form the gut

• Elie Metchnikoff, critic of Haeckel, instead proposed Phagocytella theory (gut forming endoderm evolved from ingression of cells)

sequence of Gastrulation in Sea urchin

1. Ingression

2. Migration

3. Invagination

4. Blastopore

5. Filopodia Pulling

6. Convergent Extension

7. Involution

Fertilization and Cortical Reaction

• Fertilization occurs in the animal pole

• Cortical cytoplasms rotates 30 degrees relaties to internal cytoplasm, exposes region of gray colored inner cytoplasm (GRAY CRESCENT POINT OF GASTRULATION)

apical constriction,bottle cells

are required, actin filaments collect at the apical edges causing constriction, causes that wedge shape in invagination

Cleavage in Mammals

Cleavage is super slow, is rotational, and is asynchronous

steps leading up to the MBT and zygotic genome being activated

changes to the DNA:Cytoplasm Ratio causes changes to cell cycle length

Tetraploid (double DNA)

Diploid (normal amount)

Haploid (half the DNA)

Nucleocytoplasmic Ratio

1. controls onset of cell cycle lengthening and 2. Midblastula transition (process of switching to maternal factors to zygotic genes)

Goals of Gastrulation

by the end of gastrulation, 3 germ layers are established (endo,meso,ecto) and AXIS OF THE ORGANISM HAS BEEN SPECIFIED

2 regions of Drosophila chromosome III contain homeotic genes

1. Antennapedia Complex - head segments

2. Bithorax Complex - abdominal segments

2 factors controlling cleavage patterns

1. Amount/distribution of yolk protein within the cytoplasm

2. factors in the egg cytoplasm that influence angle of the mitotic spindle and timing of its formation

Gastrulation in chicks

Primitive Streak : equivalent to blastopore lip in amphibians, migration of mesoderm and endoderm cells

gastrulation in mammals

gastrulation begins at the posterior end of the embryo where primitive streak arises

Find it, Lose it, Move it Experiments - Bicoid and anterior development

Find it: normal development, bicoid localized at the anterior front (head formation), in situ hybridization

Lose it: no bicoid at all, results in two tails and no head, bicoid is necessary for head formation

Move it: add bicoid to front (normal development), add bicoid to middle (head forms in middle), add to back (two heads): bicoid is sufficient to specifiy head whereever its placed

Secondary Mesenchyme Cells (SMCs) pull through the last stage of elongation of the archenteron (primitive gut)

Filopodial processes: extend from non skeletogenic mesenchyme located at the tip of the archenteron

Characteristic “necking” due to physical pulling forces

Laser Ablation of SMCs and filopodia

• use laser ablation of SMCs and their filopodia to see if they are necessary for elongation

• measure length of the archenteron to assess changes in elongation

• SMC Filopodia pulling is required for last third of archenteron extension

molecular link that pulls the gut up

INTEGRINS, bL integrin mRNA and protein are expressed in the SMC . integrin is necessary for the gut elongation

homeotic transformations

a structure or whole region along the axis is replaced with a structure from a different axial region

Find it experiment

IN SITU HYBRIDIZATION

localization of PROTEIN

immunocytochemistry/immunohistochemistry