CWRU Bio 216 Exam 1 Kuemerle

primordial germ cells (PGCs)

specific precursor cells that eventually undergo gametogenesis to become sperm or egg

"P granules"

RNA and protein complexes that move to the posterior end of the zygote before the first cleavage and are found in adult germ cells (C. elegans)

SOX9 and FGF9

tfs activated by SRY in males

RSPO9 and WNT4

tfs activated in females

Aneuploidy

Abnormal number of chromosomes

Mitosis during Gametogenesis

purpose: expand PGC population

interphase includes G1 (normal growth), S (DNA rep), G2 (increased growth)

this is a CYCLE

Meiosis during Gametogenesis

develops egg or sperm for reproduction

independent assortment and crossing over cause genetic variation

cells are n (haploid) after meiosis I

this is a ONE WAY process

Oogenesis

PGCs become oogonium, then the primary oocyte begins meiosis and is arrested at PROPHASE I

This 2n cell splits into a polar body and a secondary oocyte (both n)

secondary oocyte begins meiosis II and is arrested at METAPHASE II

ovulation releases secondary oocyte and it matures when combined with sperm and meiosis II resumes

corpus luteum

forms from ruptured follicle and produces progesterone to thicken uterine lining

Spermatogenesis

PGCs become spermagonial stem cell (2n) then divide into spermatogonium and primary spermatocyte (can produce sperm)

2 secondary spermatocytes form (n) then divide into 4 spermatids that mature into 4 sperm cells (n)

inhibin

prevents sperm formation through negative feedback by inhibiting FSH secretion

male hormone secretion

LH: simulates testosterone production from Leydig

Leydig: promotes spermatogenesis

Testosterone: inhibits LH and GnRH production

FSH: stimulates Sertoli cells to secrete inhibin

menstrual cycle

Days 1-7: primary oocyte releases estrogen to inhibit LH and FSH

Days 8-13: LH and FSH cause ovum release; estrogen peaks

Day 14: follicle ruptures and ovulation begins; LH and FSH peak

Days 15-28: progesterone peaks and follicle degenerates if not fertilized

acrosome reaction

1) sperm head fuses with egg and releases digestive enzymes

2) acrosomal process is extended by polymerized actin monomers

sea urchin fertilization

EXTERNAL fertilization

1 sec: sperm contacts jelly egg coat

2 sec: acrosome breaks down jelly coat and bindin binds to the vitelline layer of the egg

20 sec: FAST block where Na+ enters egg; CORTICAL/SLOW block where Ca+ is released and vitelline layer hardens

5-40 min: egg is activated and increases metabolism to prep for first division at 90 min

mammalian fertization

INTERNAL fertilization

1) capacitation removes proteins from acrosome so sperm can be more motile and bind; triggered by basic HCO3- in vagina (5-6 hrs)

2) acrosomal enzymes dissolve zona pellucida (ECM of egg) and Ca+ flows in

3) sperm bind to zp3; zp2 and zp3 are cleaved and causes BLOCK

4) oocyte has 2nd meiotic division forming n ovum and polar body (12-36 hrs)

5) sperm and egg fuse DNA

sea urchin cleavage

cell divisions with no significant growth - very rapid with no interphase

it partitions embryo into blastomeres

blastula created after 5-7 cleavage divisions and its a hollow cell ball with a fluid-filled cavity

yolk distribution

influences cleavage pattern

vegetal: most concentrated yolk amount

animal: opposite of vegetal pole

furrow: indentation on embryo surface

cytoplasmic determinants

needed for blastomere development

regulates gene expression in egg

holoblastic cleavage

frogs, mammals, sea urchins

cleavage furrow passes entirely through yolk

meroblastic cleavage

birds, fish, reptiles

too much yolk and furrow can't pass through

gastrulation

cell movements reorganize the blastula into a multilayered organism

forms ecto (skin and nervous), meso (skeleton, muscles, organs), and endo (linings) derms

primitive streak starts to form and create left/right body axes

4 extraembryonic membranes form: amnion (amniotic sac), yolk sac, allantois (nutrition, excretion, gas exchange), chorion

gastrulation movements

invagination: sheets bend inward

ingression: leave sheet and become moving mesenchyme cells

involution: sheets roll inward to form underlying layer

epiboly: sheet of cells spreads by thinning

intercalation: cell rows move between each other

convergent extension: intercalation but very directional

archenteron

future digestive tract formed during gastrulation running from vegetal to animal poles

blastopore on vegetal pole will become anus

stage is called gastrula

Protostone

mouth first

worm

Deuterostome

anus first

urchin

blastoderm

ongoing cleavage where the area pellucida marks location of gastrulation to begin (13 days after fert)

7 days after fert - epiblast: surface layer that becomes ecto, meso, and endo

hypoblast: extraembryonic cell tissue for external membranes and chemical signals

blastula forms blastocyst

in mammals after cleavage produces 100+ cells two layers form

inner cell mass: develops into embryo

trophoblast: fetal part of placenta

chorion

fetal part of placenta that will give rise to chorionic villi for nutrient transfer

placenta

temporary organ developed on implantation of blastocyst

amnion (inner), allantois (middle), chorion (outer) layers

neurulation in humans

18 days: neural plate invaginates to form neural groove

20 days: neural folds approach and fuse at midline and groove becomes neural tube

primary: neural plate creases until edges fuse

secondary: tube forms by hollowing out solid interior

becomes brain and spinal cord (24-26 days)

somites: formed by meso and become vertebrae

cadherins: transmembrane proteins for cell adhesion

body plan

frogs

A/P determined at oogenesis

D/V determined at fertilization

chicks

A/P based on gravity in oviducts

D/V based on pH differences in blastoderm

pattern formation

morphogen: diffuses as product of genes or signaling molecules

Bicoid (two tailed)

maternal effect gene: mutant in mom causes mutant phenotype in offspring

sets up anterior end of fly so mutation caused posterior structures at both ends

limb bud development

AER: dense ecto at outer edge of bud that lead to P/D organization and limb bud outgrowth

ZPA: meso tissue on posterior end that sets up A/P; close to ZPA creates posterior structures and far from ZPA produces anterior

ZPA secrete Shh protein that specifies limb growth and digits

Hox genes

fundamental for A/P axis in animals

can repress on one gene and activate another

specifies positional identity NOT specific structures

cell differentiation

differences between cells come from gene expression differences NOT different genomes

can genes be irreversibly inactivated during differentiation?

totipotent

ability to give rise to every type of cell in adult body

zygote

pluripotent

ability to give rise to many cell types / any of three germ layers

inner cell mass of blastocyst

multipotent

ability to differentiate into a few cell types

bone marrow cells

Somatic Cell Nuclear Transfer (SCNT)

Dolly the sheep

mammary cells nutrient deprived to induce de-differentiation

cells fused with enucleated egg from donor sheep

mitosis stimulating inducers to form embryos

embryo placed in surrogate

cells could have aged prematurely due to incomplete reprogramming to totipotent stem cells

epigenetics

changes in gene expression that do not change DNA sequence

methyl groups to cytosine that causes repression

acetyl groups to histones to expose/uncoil DNA

differentiated cells have more methylation

induced pluripotent stem cells (iPSCs)

adult cells genetically reprogrammed to an ESC state due to forced gene expression (don't need to destroy embryos anymore)

retrovirus to get master regulatory genes into PSCs (reverse transcriptase for replication)

differences in iPSCs and ESCs due to methylation

retrovirus can randomly insert genes causing mutations and cancer

CRISPR Cas9

prokaryotic DNA segments with short base sequence repeats interspersed from viruses followed by spacer DNA

Cas9 nuclease allows to target specific DNA sites to knock out, insert, up or down regulate, or tag genes

crRNA binds to targeted DNA sequence, tracrRNA bps with crRNA so Cas9 can locate target

PAM is DNA on target DNA so Cas9 can bind