Endocardium Directs Cardiomyocyte Movement during Heart Tube Assembly

1
Endocardium Directs Cardiomyocyte Movement during
Heart Tube Assembly Nathalia Glickman
Holtzman October 22, 2007
2
Development
Nicholas Hartsoeker 1695
3
Organogenesis
4
Heart Development
Frog
Yutzey and Kirby, Dev Dyn 2002
5
Heart Development in Humans
Human Heart
Human Heart Defect
6
Why Zebrafish?

• small
• develop quickly
• develop externally
• vertebrate
• optically clear
• suitable for classical development and genetic
  studies

7
Zebrafish Heart

• complex structure derived from simple form
• composed of two cell layers
• two chambers with distinct properties

How is this complex structure made?
8
What Cell Behaviors Drive Heart Formation?
26 hpf
cmlc2
9
Tg (cmlc2GFP) Transgenic
Fish from Huai-Jen Tsai
48h lateral view
10
GFP Mimics cmlc2 Expression
early
Phase 1
Phase 2
11
Tg(cmlc2gfp) to Observe Cell Movement
early
time interval 2 min/frame
12
What Cell Behaviors Drive Heart Formation?

• do the cells move as individuals or as a
  coherent population?
• what direction do they move?
• how fast do they move?
• are rate and direction position or time
  dependent?
• what regulates the observed movements?

13
Initial Coherent Medial Movement
wt
16 somites
t0 min
t30 min
t60 min
14
Medial Movement is not Position Dependent
15
Phase 1 Movement

• all the cells move together as a coherent group.
• cardiac field moves directly towards the
  midline.
• there is no position dependence to cell movement
  during this phase.

Medial Movement
16
Myocardium is an Epithelium

• the myocardium is a developing epithelium.
• cells in an epithelium move as a coherent group.
• cells in an epithelium do not change neighbors

Trinh and Stainier, Dev Cell, 2004
17
What happens next?
18
Transition to Angular Movement
19
Angular Movement is Position Dependent
20
Phase 2 Movement

• all the cells move together as a coherent group.
• anterior and posterior cells move angularly.
• central cells continue to move medially.

21
Endocardium Directs Angular Movement
E
E
E

• we propose that these two phases of movement are
  independently regulated.

• to test whether the endocardium influences the
  redirection we examine movement in cloche mutant
  embryos.

22
Cloche Mutants Lack Endocardium but still make a
Heart Tube
Stainier et al, Dev,1995
wt
cloche
23
Angular Movement Requires Endocardium
cloche
t0 min
t30 min
t60 min
24
No Angular Movement Without Endocardium
25
Summary of cloche

• endocardium is required to direct the transition
  to angular movement.
• the endocardium could be acting as an attractant
  or/and a barrier.
• is angular movement dependent on medial movement?

26
Barrier vs Attractant
27
Cardia Bifida Mutant miles apart
wt
miles apart
28
What Regulates these Movements?

• attractants from the contra-lateral myocardium?

How do we test this?

• we can take advantage of zebrafish mutants that
  prevent juxtaposition of the heart fields.

29
Cell Movement in miles apart
miles apart
left heart field
t0 min
t60 min
30
Observe Cell Movements in miles apart
31
Summary of miles apart

• no medial movement in miles apart mutants.
• medial movement is not required for angular
  movement.
• is this angular movement endocardium dependent?

• examine cell movements in double mutants.

32
Cell Movement in double mutant
miles apart/cloche
left heart field
t0 min
t60 min
33
Observe Cell Movements in double mutant
miles apart
double
34
No Net Cell Movement in double mutant

• endocardium is not acting exclusively as a
  barrier, it also promotes movement.

35
Barrier vs Attractant
36
Summary of Cell Movement
wt
37
Endocardium Actively Directs Cell Movement
E
E
E

• cardiac fusion involves two morphologically and
  genetically separable phases of cell movement.
• the endocardium actively initiates movement.
• the endocardium provides directional information.

38
Charachterizing the Endocardium
39
Distinct Endocardial Populations
40
New Model of Endocardium
E
1. Model of endocardial morphogenesis. 2. What is
the role of the newly identified, molecularly and
morphologically distinct endocardial cells?
41
Model of Endoderm Migration
42
Time-lapse of Endothelium
Not quite as predicted
43
They are required for myocardial morphogenesis
44
Loss of ring results in disrupted cardiac
morphology
Perhaps the endocardial ring defines lumen size
because the endocardium acts as a scaffold for
myocardial morphogenesis.
45
Models
46
Time-lapse of Endothelium
Not quite as predicted
47
Models
48
Strategies for Disrupting Endothelium
49
How is the Endocardium Regulating Direction of
Movement?

• examine the location of the endocardium relative
  to the myocardium during heart tube formation.
• examine the expression of candidate molecules in
  the endocardium and myocardium.
• test the role of these molecules by via GOF, LOF
  and mis-expression studies.

50
Thank You To
Primiline Courtney Kevin Werkheiser Assal
Hakhanjani Corinna Singleman
Huai-Jen Tsai
Debbie Yelon
51
(No Transcript)