Lecture 4 (2a) Homeodomain Proteins & Hox Genes

Question 1

Homeodomain proteins

Answer 1

• determine the identity of individual segments along the anterior-posterior body axis
• determine regional identity in developing limbs along the anterior-posterior and proximal-distal axis
• determine regional identity in developing nervous system along the dorso-ventral axis
• every segment is different
• during segmentation given identity

Question 2

Homeodomain proteins are

Answer 2

transcription factors

• must recognize portion of domain

Question 3

homeodomain coded by a 180-base-pair DNA sequence known as the

Answer 3

homeobox

Question 4

Homeodomain folds into

Answer 4

3 α-helices

Question 5

Helix _ binds DNA

Answer 5

3

Question 6

Parts of the homeobox

Answer 6

are conserved in all homeodomain proteins

Question 7

A four base pair motif … is conserved in nearly all sites recognized by homeodomains

Answer 7

TAAT is conserved

Question 8

All homeodomain binding is destroyed if

Answer 8

the first T is mutated

Question 9

The base pairs following the TAAT motif determine

Answer 9

which homeodomain protein recognizes the DNA binding site

TAAT / specific
general) (eg boicoid GC) (eg ANTP TA

Question 10

In individual homeodomain proteins specific amino acids

Answer 10

recognize the base pairs in the DNA binding site

Question 11

Morphologically visible segments and identity appear

Answer 11

at the same time

Question 12

Homeotic selector genes in Drosophila are

Answer 12

homeodomain proteins that determine the identity of the individual segments along the anterior-posterior axis

Question 13

Homeotic selector genes are arranged in

Answer 13

2 gene complexes
• antennapedia complex
• bithorax complex

(on chromosome same as expressed in embryo)

Question 14

Gap and pair-rule genes set up the

Answer 14

initial domains of the homeotic gene

Question 15

Homeotic selector genes are expressed in

Answer 15

a parasegmental pattern

Question 16

The expression of a homeotic gene is repressed by

Answer 16

all homeotic gene products expressed posterior to it

TURNS INTO ONE ANTERIOR TO IT ALWAYS

Question 17

Homeotic mutations result in

Answer 17

transformations

Question 18

Ubx mutant

Answer 18

2 pairs of wings

• 3rd T segment turns into 2nd T segment

Question 19

If the bithorax complex is missing

Answer 19

all segments are transformed into the 2nd thoracic segment

Question 20

Posterior abdominal segments are transformed into

Answer 20

more anterior abdominal segments in

abd-A and abd-B mutant embryos

Question 21

Homeotic mutation that converts antennae into legs

Answer 21

• ANTP mis-expression

* ANTP in T segment represses genes anterior to it (antennae and eyes) and switch on downstream

Question 22

How do homeotic genes determine the identity of individual segments?

Answer 22

homeotic genes activate or repress Realisator Genes

```
Antennapedia inhibits
• antenna forming genes
• eye forming gene
eyeless/Pax6
and posterior
~~~

Question 23

Ultrabithorax represses

Answer 23

wing development

Question 24

The order of Hox genes is similar between

Answer 24

insects and mammals

• we have overlapping patterns and more Hox genes

Question 25

Hox 10 knockout

Answer 25

transformation of lumbar into thoracic vertebrae

Question 26

Expansion of Hox 10 –>

Answer 26

Hox 11 knockout

Question 27

Hox 11 knockout

Answer 27

transformation of sacral into lumbar vertebrae

Question 28

A code of differing Hox gene expression determines

Answer 28

the type of vertebrae formed

segmented structures of mesoderm

Question 29

In vertebrates, there are hox genes

Answer 29

for limbs (prox/dist) as well as anterior-posterior axis

Question 30

Hox genes prepattern the

Answer 30

limb bud along the anterior-posterior axis

Question 31

There may be 1 enhancer for

Answer 31

many genes

And many enhancers for 1 gene

Question 32

Mutations in Hox 11, 12, and 13 in early limb buds lead to a loss of

Answer 32

ASYMMETRY

Question 33

Hox gene expression changes

Answer 33

during the development of the limbs

Question 34

Shh is a

Answer 34

transcription factor

Question 35

The late expression of Hox genes is required for

Answer 35

patterning of the proximal-distal limb axis

overlapping –> structures form on prox/dist axis

Question 36

Radius and ulna are missing in

Answer 36

Hox-11 deficient mouse mutants

Question 37

Mutations in Hox 13 humans lead to

Answer 37

polysyndactyly - “many fingers joint together”

ant/post axis

Question 38

Homeodomain proteins determine

Answer 38

regional identity along the dorso-ventral axis

patterning of the nervous system

Question 39

Homeodomain proteins … … and … subdivide the neuroectoderm into 3 dorso-ventral regions

Answer 39

• Msh
• Ind
• Vnd

specific neurons formed in different areas

Question 40

The dorso-ventral homeodomain proteins are conserved in

Answer 40

vertebrates although the nerve cord is dorsal

Question 41

Homeodomain proteins determine the

Answer 41

identity of body segments along the anterior-posterior axis

Question 42

Homoetic selector genes are arranged on the chromosome(s)

Answer 42

in the same sequence as they are expressed along the anterior-posterior axis

Question 43

Mutations in homeotic selector genes result in

Answer 43

transformations

Question 44

Vertebrate Hox genes determine the identity of the

Answer 44

vertebrae along the anterior-posterior axis

Question 45

Vertebrate hox genes are required for

Answer 45

patterning the anterior-posterior and proximal-distal axis in the developing limb

Question 46

Homoedomain proteins establish regional identity in the

Answer 46

neuroectoderm along the dorso-ventral axis, both in vertebrates and invertebrates

Question 47

Antennapedia inhibits

Answer 47

• antenna forming genes
• eye forming gene
(eyeless/Pax6)
and posterior