M2. development of xenopus laevis

Question 1

the vertebrate body plan

Answer 1

-similar basic body plan

Question 2

vertebral column

Answer 2

segmented backbone surrounding the spinal cord

Question 3

anterior-posterior axis

Answer 3

• head - trunk - tail

- head end enclosed in a skull (bone or cartilage)

Question 4

dorsal-ventral axis

Answer 4

• spinal cord (d)

- mouth (v)

Question 5

bilateral symmetry

Answer 5

dorsal midline

Question 6

phylotypic stage

Answer 6

-all chordate embryos pass through the phylotypic stage
(embryos are similar in appearance)
-common features : head, notochord, neural tube (earliest appearance of nervous system), somites (blocks of mesoderm)

Question 7

all vertebrate embryos undergo a similar pattern of development

Answer 7

• gametogenesis
• fertilization
• cleavage
• gastrulation
• notochord formation
• neurulation
• somitogenesis
• organogenesis

Question 8

cleavage

Answer 8

earliest cell division, rapid cell division through which embryo becomes divided into smaller cells

Question 9

gastrulation

Answer 9

dynamic process through three germ layeter (ectoderm, mesoderm, endoderm) organize themselves

Question 10

notochord formation

Answer 10

column of mesoderm located just ventral to neural tube

Question 11

neurulation

Answer 11

formation of the neural tube - precursor to nerve cord

Question 12

somitogenesis

Answer 12

formation of regularly spaced blocks of mesoderm (somites) flaking notochord that give rise to skeleton and muscle

Question 13

organogenesis

Answer 13

development of organs

Question 14

model amphibian embryo: xenopus laevis

Answer 14

• basis for what we know about early development of the embryo
• embryos are large (scaled bar 0.5mm) - allowed for dissection of the early embryo
• dissected tissues easy to culture

Question 15

xenopus laevis: egg

Answer 15

• egg has a distinct polarity –> animal to vegetal axis (bar 1mm)
• dark pigmented animal region and heavier yolk vegetal region
• sperm enters animal region
• zygote is diploid (2N)
• first cleavage along animal -vegetal axis

Question 16

xenopus blastulation: cleavage of the embryo to form blastomeres

Answer 16

• first cleavage along A/V axis, divides egg in left -right
• second cleavage 90 degrees to first cleavage
• third cleavage equatorial and asymmetric - four small animal and four small vegetal cells, eight total blastomeres

Question 17

blastula

Answer 17

germ layers start to form
(ectoderm, endoderm, mesoderm)

an animal embryo at the early stage of development when it is a hollow ball of cells.

Question 18

blastula stage :

Answer 18

• reached after 12 divisions (~4096 cells)
• has radial symmetry (ie. no visible sign of A/P or D/V axis)
• has blastocoel
• marginal zone

Question 19

blastocoel

Answer 19

a fluid filled cavity in animal region

Question 20

marginal zone

Answer 20

equatorial ring around embryo separating animal and vegetal region

Question 21

ectoderm

Answer 21

animal region- epidermis and nervous system

Question 22

mesoderm

Answer 22

marginal zone - muscle, bone, blood, heart

Question 23

endoderm

Answer 23

vegetal zone - intestine , lungs, liver, pancreas

Question 24

xenopus laevis : gastrulation

Answer 24

the morphogenic process occurring in three dimensions where endoderm and mesoderm are internalized
-blastopore

Question 25

blastopore

Answer 25

small slit like in folding of marginal zone on dorsal side, site of embryonic organizer (i.e. Spemann-Mangold organizer) -organized dorsal development and antero-posterior axis

Question 26

gastrula mesoderm and endoderm

Answer 26

enter blastopore and migrate (via involution) to the future anterior of the embryo -first tissues to enter the embryo are most anterior

Question 27

involution

Answer 27

germ layer migrate as a coherent sheet of cells

Question 28

gastrula : ventral and dorsal

Answer 28

ventral side initiates involution after dorsal side - delayed but similar cell movement occur on ventral side - epiboly - all three layers change shape and elongate

Question 29

epiboly

Answer 29

ectoderm spreads to cover embryo

Question 30

gastrula: archentron

Answer 30

a second cavity forms during gastrulation (future gut cavity) --> blastocoel reduces in size -mesoderm and endoderm spread to the left and right of the midline -lateral mesoderm spreads ventrally to cover inside of archenteron

Question 31

late gastrulation

Answer 31

- blastopore closed (future anus) - the mesoderm contacts both the ectoderm and endoderm along the antero -posterior axis - mesoderm is patterned along its antero-posterior axis via the action of the organizer - ectoderm covers embryo - yolk cells remain as food source

Question 32

neurulation

Answer 32

- dorsal mesoderm starts to develop into notochord (rod along dorsal midline) and somites (segmented blocks of mesoderm along notochord) - lateral mesoderm (lateral plate mesoderm) will form mesoderm derived organs (i.e. heart (A) kidneys (P))

Question 33

neurulation: neurula stage

Answer 33

formation of the neural tube (precursor to central nervous system)

Question 34

neurulation: nerual plate

Answer 34

is the ectoderm located above notochord and somites - edge of the neural plate forms neural folds which rise towards midline and fuse to form neural tube - the neural tubes sinks below epidermis - the anterior neural tube becomes brain- middle and posterior neural tube becomes spinal cord

Question 35

early tail bud stage: dorsal part of somites

Answer 35

become dermatome (future dermis)

Question 36

early tail bud stage : ventral somite

Answer 36

becomes vertebrae, trunk and limb muscles

Question 37

early tail bud stage : lateral plate mesoderm

Answer 37

heart, kidney, gonads and gut muscles

Question 38

early tail bud stage: ventral mesoderm blood

Answer 38

forming tissues

Question 39

early tail bud stage : endoderm

Answer 39

lining of the intestine, liver, pancreas, and lungs

Question 40

early tail bud stage: after neurulation

Answer 40

neural tube closure, the tail bud stage occurs

Question 41

early tail bud stage: the brain

Answer 41

anterior neural tube, is divided into forebrain, midbrain and hindbrain

Question 42

early tail bud stage: organogenesis initiates

Answer 42

eyes and ears start to develop

Question 43

early tail bud stage: three branchial arches form

Answer 43

form jaws and bones of the face

Question 44

early tail bud stage: neural crest cells

Answer 44

come from the edges of the neural folds after neural tube fusion -they detach and migrate as single cells b/w the mesodermal tissues to become the sensory and autonomic nervous system pigment cells and some cartilage of skull