Heart Development

Question 1

What are the two origins of the heart?

Answer 1

1. two lateral patches of cells on either side of the embryo in the splanchnic lateral plate mesoderm. Specified by wnt inhibitors, FGF8, and BMPs from the endoderm
2. The cardiogenic mesoderm forms a heart tube through embryonic folding and fusion. Atria are specified by retinoic acid

Question 2

What layers form when the lateral plate mesoderm splits?

Answer 2

1. The somatic lateral plate mesoderm
   - develops in close association with ectoderm
   - forms ventral domains of the dermis, and bones of limbs
2. The splanchnic lateral plate mesoderm
3. In-between these layers becomes the abdominal cavity (coelom)

Question 3

When does embryonic folding occur?

Answer 3

4th week (day 20-21)

Question 4

What is the purpose of embryonic folding?

Answer 4

Creates the coelom, brings the two heart rudiments together at the midline

Question 5

When does the heart start beating?

Answer 5

Day 22

Question 6

What is the source for Wnt inhibitors and BMPs?

Answer 6

The underlying anterior endoderm. These are necessary for induction of the cardiogenic mesoderm

Question 7

What transcription factors do BMPs activate for heart development?

Answer 7

Nik2.5 - activates cardiac specific genes

Question 8

Where are the Wnt inhibitors expressed?

Answer 8

Anteriorly, there is high Wnt expression posteriorly

Question 9

Where are BMPs expressed?

Answer 9

• High anterior laterally (expressed around the top)

- Inhibited at the midline

Question 10

What is expressed anteriorly for heart development?

Answer 10

BMP and FGF8

- high FGF8 in the cardiac crescent

Question 11

What structure is induced from the expression of BMPs and FGF8?

Answer 11

The cardiogenic mesoderm

Question 12

What structure is induced from the expression of BMPs and Wnt

Answer 12

The hemangiogenic mesoderm

Question 13

What is retinoic acid used for in heart development? Where is it expressed? (anterior vs posterior)

Answer 13

RA specifies the atria and sinus venosus (inflow tracts). It is expressed posteriorly.

Question 14

What is the function of Rahld2?

Answer 14

The enzyme that produces retinoic acid from retinol

Question 15

How do the atria move from their posterior position to above the heart?

Answer 15

Cardiac looping occurs to change the heart from a tube to a 4 chambered heart. The atria loop to the left and the ventricles shift to the right a little bit (normally, unless you have situs inversus)

Question 16

When is cardiac looping done?

Answer 16

Day 28, it starts day 23

Question 17

Which genes are needed to determine the direction that the heart loops in?

Answer 17

Nodal and Pitx2

Question 18

True/False. Tbx2 is not needed for heart development

Answer 18

False

Question 19

When and where do blood islands form?

Answer 19

Form at day 17, they form in the splanchnic mesoderm of the yolk sac

Question 20

When does vasculogenesis begin?

Answer 20

Day 18 (3 days before heart tubes fuse)