Development and Pattern Formation

Question 1

central problems of developmental biology

Answer 1

cell fate specification

pattern formation

Question 2

patternf formation

Answer 2

the organization of embryonic cells into a 3-dimensional body plan

Question 3

What initiates pattern formation?

Answer 3

the establishment of axes

expression of different genes along an axis

expression of a single gene in a concentration gradient along an axis

Question 4

primary patterning

Answer 4

establishes the body axes

Question 5

secondary patterning

Answer 5

establishes regional or organ specific axes

Question 6

At what point in development does patterning take place in humans?

Answer 6

mainly during weeks 4-8 of embryonic development

Question 7

trhee functional classes of genes regulating fly development

Answer 7

1) maternal-effect genes
2) segmentation genes
3) homeotic genes

Question 8

three types of segmentation genes in fly development

Answer 8

1) gap genes
2) pair rule genes
3) segment polarity genes

Question 9

maternal effect genes

Answer 9

express in the drosophila egg before fertilization

Question 10

gap segmentation genes

Answer 10

divide the embryo into broad bands

Question 11

pair rule genes

Answer 11

further divide the embryo

Question 12

segment polarity genes

Answer 12

divide the embryo into the final segments that are present in the adult animals

Question 13

homeotic genes

Answer 13

genes that determine the fate or identity of body segments during development

Question 14

HOX genes

Answer 14

first homeotic genes identified in Drosophila

all HOX genes contain a 183 bp motif called the “homeobox”

encode proteins containing a 51 amino acid binding motif called the “homeodomain”

function as transcription factors

Question 15

vertebrate HOX genes

Answer 15

organized into 4 different complexes (A-D) on 4 different chromosomes

reason for multiple complexes is unclear, may be that developmental events are more complex and redundancy ensures normal development

Question 16

How does the location of a HOX gene in the complex correlate to its expression pattern?

Answer 16

genes closer to the 3’ end of the complex have expression patterns that are further anterior to the embryo

Question 17

two types of colinearity

Answer 17

temporal colinearity

spatial colinearity

Question 18

spatial colinearity

Answer 18

the order of genes in a cluster/complex maps an axis in the developing embryo

Question 19

temporal colinearity

Answer 19

the order of genes reflects their temporal expression during development

Question 20

HOX A1 knockout

Answer 20

delayed closure of neural tuve in the hindbrain region, absence of several cranial nerve motor nuclei and sensory ganglia, inner ear defects and basal skull anomalies

Question 21

HOX A3 kockout

Answer 21

craniofacial, thyroid, thymic, and cardiac anomalies

Question 22

HOX B4 knockout

Answer 22

second cervical vertebra, the axis, transformed into a duplicate first cervical vertebra, the atlas

Question 23

posterior dominance of HOX genes

Answer 23

when more than one HOX gene is expressed in a given segment, the HOX gene whose epxression pattern ends more posterior defines the phenotype of that segment

Question 24

HOX D4 Ectopic anterior expression

Answer 24

occipital bones transformed into “cervical” vertebrae

Question 25

rules governing HOX gene expression and function in mammals

Answer 25

temporal and spatial colinear expression

more HOX genes are expressed in posterior regions

if two HOX genes have overlapping expression patterns, the HOX gene whose expression ends further posterior will be dominant over the HOX gene whose expression pattern extends more anterior

considerable redundancy in function has been demonstrated between paralogous groups of HOX genes

HOX genes demonstrate colinear expression along the anterior-posterior axis of the mbryo as well as along other embryonic axes, including the limbs, GI tract, and female GU tract

Question 26

mutation of human HOX D13

Answer 26

causes synpolydactyly

autosomal dominant trait with incomplete penetrance

maps to 2q, the region of the HOX D cluster

sequence analysis demonstrated expansions of a polyalanine stretch in the amino terminal region

Question 27

hedgehog in Drosophila

Answer 27

segment polarity segmentation gene

later in development, necessary for patterning imaginal discs and the dorsal epidermis

Question 28

mammalian hedgehog genes

Answer 28

three have been identified: sonic hedgehog, indian hedgehog, and desert hedgehog

secreted proteins from organizing center sand epithelium during development

Question 29

organizing centers in the developing limb

Answer 29

zone of polarizing activity (ZPA)

apical ectodermal ridge (AER)

nonridge (dorsal) ectoderm

Question 30

zone of polarizing activity (ZPA)

Answer 30

located in the proximal, posterior part of the limb bud

Shh is the signaling molecule

defines an anterior-posterior limb axis

Question 31

apical ectodermal ridge (AER)

Answer 31

located in the distal edge of the limb bud

FGFs represent the signaling molecules

defines a proximal-distal limb axis

Question 32

nonridge (dorsal) ectoderm

Answer 32

located on the dorsal aspect of the limb bud

Wnt-7a represents a signaling molecule

defines a dorsal-ventral limb axis

Question 33

Describe hedgehog signaling in vertebrates

Answer 33

Hh inhibits Ptc, which leads to the activation of smoothened and GLI-1,2,3

this activates cell growth and differentiation pathways

Question 34

holoprosencephaly

Answer 34

failure of prechordal mesenchyme migration and lack of sonic hedgehog inductive events, loss of function

causes abnormal septation of cerebral hemispheres and abnormality in the development of the ventral embryonic forebrain

Question 35

What nervous system structures form due to high concentrations of Shh?

Answer 35

ventral floor plate and motor nuerons in the ventral neural tube

Question 36

What nervous system structures differentiate from areas of the neural tube with lower concentrations of Shh?

Answer 36

dorsal areas of the tube differentiate into sensory ganglia/neurons

Question 37

ventral-medial somite

Answer 37

the closest to the notochord, very high concentration of Shh, differentiates into the sclerotome

Question 38

sclerotome

Answer 38

differentiates into vertebral bodies and ribs

Question 39

dermomyotome

Answer 39

precursor of dermis and the body musculature

Question 40

basal cell nevus syndrome

Answer 40

arises because of constitutive activation of Patched

leads to skull and rib abnormalities with a predisposition to cancer