fertilisation Flashcards
four stages of fertilisation
- sperm capacitation
- sperm activation & interaction w oocyte
- activation of oocyte
- syngamy
sperm capacitation
- strip glycoproteins so less stable
- Ca2+ influx > PKA phosphorylate Tyr > less stable > fuse with oocyte
examples of sperm acrosomal contents
- hyaluronidase, required to digest matrix between cumulus cells to expose ZP
- acrosin, enzyme that digests ZP
deacribe sperm activation
- induced by binding to ZP
- acrosome swells, membrane fuses
- activation of PKC > whiplash movement
describe sperm binding + fusion
- in perivitelline space, microvilli from equatorial side bind to & envelop sperm head
- involves equatorial and postacrosomal
membranes on oocyte and sperm respectively - sperm stops moving, membranes fuse
molecules for sperm binding and fusion
Izumo1 (sperm)
Juno (oocyte)
CD9 (tetraspanin on oocyte)
activation of oocyte
- increases in [Ca2+]i
- by PLC-zeta from sperm
- occurs in waves from site of sperm entry
- every 3-15 min for next 4-5h
cortical reaction is produced by ? and involves ?
produced by elevated Ca
involves release into the perivitelline space of:
- ovastatin, so cleavage of ZP3/4 and ZP2
- ZP crosslinks
- Juno exocytosed off oocyte membrane
sequence of events leading to syngamy
- during oocyte-sperm fusion and second polar body expulsion, cytoplasmic sperm contents > oocyte cytoplasm
- sperm nuclear breaks down, protamines replaced with histones, chromatin unwinds. induced by oocyte factors
- paternal and maternal pronuclei form. move from subcortical position to centre of zygote. then DNA synthesis occurs to prep for first mitotic division
- membranes break down, mitotic spindle forms, chromosomes line up at equator
- syngamy = final phase of fertilisation; gametic chromosomes come together
- immediate first cell division
parental contribution to offspring - structures
maternal: everything
paternal: centriole and pericentriolar material to make up centromere, ncRNA (proteins broken down, mitochondria don’t survive)
why paternal mitochondria is broken down
- might be mutated by oxidative stress
- exposed to ROS from leucocytes in epididymus, during transit, and through sperm movements
- poor quality sperm have mutations & deletions in mtDNA
are all mitochondrial diseases maternally-inherited
no, 85% aren’t because nuclear DNA encodes for genes involved in mt function
types of chromosomal anomalies
- errors of ploidy - won’t survive
- errors of somy, e.g. trisomy 21
- translocations
- genetic mosaics (number of nuclei, chromosomal composition)
causes of aneuploidy
- failure of polar body formation, cleavage division, or polyspermy
- problems with oocyte meiotic divisions
- events in ovaries/testes (mutagens)
- alcohol, anaesthesia
- increased maternal age
(germ cells have less surveillance for mutations because need genetic diversity)
parthenotes only having maternal chr are called
gynogenetic
can gynogenetic parthenotes survive
only until first cleavage cause then no centriole
complete hydratidiform moles - genetic makeup, cause
- 46XX or 46XY; all of paternal origin
- female pronucleus is lost + 2 sperm fertilise egg, or 1 sperm but duplicates
partial hydratidiform moles - genetics
69XXX or 69XXY (cause 1 sperm duplicates or 2 sperm fertilise)
example of unequal genetic contribution
IGF2/H19
