Heart development

Document Sample
Heart development Powered By Docstoc
					   Heart
Development
  Iain Farrance
  January 27, 2009
   Cardiac vs. skeletal muscle
                          Cardiac                Skeletal
Embryonic origin         Lateral plate           Pre-somitic
                          mesoderm               mesoderm
Determination          No one Master                myoD
genes
Differentiation and   Emb: not exclusive    Exclusive all the time
cell division          Adult: exclusive
Genes expressed                 Common and unique

Repair of damaged     None or very little       Satellite cells
muscle

                                                                  2
Morphogenesis and fate of the Heart
                                                                                     4. Developed
     1. Precardiac mesoderm   2. Linear Heart tube   3. Looping Heart tube
                                                                                         Heart




 Human

 Mouse ED 7.5                    ED 8.5                  ED 8.5-9.5          ED 12

 Chick    19-22 hrs              28 hrs                    3d                           4-5 d

                                                                                                    3
1. Precardiac
 mesoderm-
 ingression




                4
1. Precardiac mesoderm- heart fields
              • Primary or First heart field
                (FHF)
                 – More anterior and lateral
                   than secondary.
                 – Marker contractile proteins
                   etc.
                 – Fate (A, LV)
                 – Differentiates early (at FHF)
              • Secondary (Anterior). SHF
                 – Medial and caudal to FHF
                 – Markers- FGF8, -10, Isl-1
                 – Fate (OFT, RV, some
                   contribution to atria)


                                               5
2. Linear heart tube




                       6
                  3. Looping heart tube




• Bends ventrally and rotates right
• Brings atria caudal to ventricles
• Beginning of chamber formation
    – Ballooning, constrictions,
• Ventricular wall thickens (compact
  layer, trabeculae)
• Mechanism involves protein
  expression, cell division
                                          7
3. Looping heart tube




Looped heart tube different view
                                   8
3. Looping heart tube- movies




                      Blood flow




                                   9
4. Migration of SHF cells into heart




                                       10
Morphogenesis and fate of the Heart
                                                                         4. Developed
 1. Precardiac mesoderm   2. Linear Heart tube   3. Looping Heart tube
                                                                             Heart




                                                                                        11
5. Chamber formation
        • Chamber myocardium (red, green and
          blue)
           – A (blue), V (red) and inflow and outflow
             vessels (green)
           – More differentiated with higher levels of
             cell division
           – Markers: Cx40, -43, chisel (cytoskeletal
             protein). NppA (ANF), N-myc
        • Non-chamber myocardium (primary
          myocardium), grey
           –   inner curvature of HT, OFT
           –   conduction tissue, septa, valves
           –   Less differentiated, lower cell division
           –   Marker Tbx2
        • Details on chamber formation
           – Ballooning of chambers due to cell
             division, cytoskeleton, differentiation
           – ventricular wall thickens
           – Outer (compact layer). Highly mitotic.
           – Inner layer (spongy) due to trabeculae
                                               12
      5. Remodeling- Septa formation
• Looping -->
  chambers in right
  position
• Septa (A, V, AV)
• Septation starts at
  looping
   – Endocardial
     cushions
   – Trabeculae fusion
• OFT septation
• Valves
   – At AVC
   – From EC
     cushions
   – FGF, IGF, NFAT,
     Msx
                                   13
4. Remodeling- Muscle growth




                               14
Non-muscle Tissues: Lineages




                           15
               Cardiac neural crest




• Outflow vessels are patterned by CNC
   – Complex changes
   – many birth defects (ex persistent truncus arteriosis)
   – outflow vessels from heart field but neural crest patterned
• CNC cells
   – migrate from neural tube to pharyngeal arches to OFT
   – pattern and contribute aortic arches (3,4 and 6)              16
Genetic and Molecular Mechanisms:
        transcription factors


                                CNC




                                      17
Nkx proteins




               18
  Nkx2.5
expression




       19
                           Nkx2.5 mutation


• NK proteins essential for cardiac lineage (tinman,
  DN proteins)
• Human mutants ASD, conduction defects
• Mouse KO arrests at loop
• Nkx2.5 not necessary for specification



                                                 20
HAND Proteins


                HAND2




                HAND1




                        21
HAND2
 KO




No PV (=RV)




         22
                          Tbx Proteins
•   Multi-gene family of transcriptional regulators
•   5 sub-groups
•   T-box DNA binding domain (to TBEs in promoters)
•   Transcriptional activators and/or repressors
•   Interactions with other transcription factors, co-regulators key to activity




                                                                           23
         Holt-Oram Syndrome: Tbx5
                                   Tbx5 regulates forelimb fate
• Syndrome
    – ASD, VSD
    – Conduction, hypo-LV
    – FORELIMB
• Tbx5, AD mutations
• Expression (heart, early limb)
    – Defects in LV growth
    – Defects in non-chamber
      derivatives
• Regulate fate of entire
  structures (limb)




                                                                  24
         Tbx2 and Tbx20 (paper)
           Tbx2                         Tbx20
• Transcriptional repressor   • Transcriptional activator and
• Expressed in non-             repressor (dependent on
  chamber (primary)             signaling molecules and
  myocardium                    cofactors)
• Represses by binding to     • Expression: FHF, then both
  TBEs                          types myocardium, then
   – ANF (differentiation)      down-regulated in chamber
   – N-myc (proliferation)      myocardium
                              • Represses Tbx2 expression
                                by direct binding to TBE
                                sites
                                                        25
 Model for Tbx and chamber development




• Chamber myocardium
   – Tbx20 represses Tbx2
   – Relieves repression of ANF and N-myc
   – Tbx5 activates via TBEs
• Non-chamber myocardium
   – Both Tbx2 and Tbx20 expressed
   – Activity of Tbx20 controlled by X factor (BMP dependent)
   – Tbx2 represses ANF and N-Myc (less differentiation and proliferation)   26
Genetic and Molecular Mechanisms:
       micro RNAs (miRNA)


                             CNC




                                   27
    Post-transcriptional gene silencing by
•   MicroRNAs (miRNAs)
                       miRNAs
    – 21-mers
    – 2-300 in Hs/Mm
• Bind to 3’-UTR of target mRNAs
    – Imperfect match
    – Inhibit translation or mRNA degradation
• Complex regulatory schemes
    –   Expression patterns change
    –   30% of genes are regulated
    –   Single miRNA can regulate from a few (<5) to many (50+)
    –   Single mRNA targeted by multiple miRNAs
• Roles of miRNAs
    – Cellular “janitors”
    – Development (heart, brain)
                                                                  28
    – Mis-regulation of miRNA in diseases. Cause or effect?
                miRNAs: mechanism
• PolII transcription
    – Intronic
    – Independently transcribed.
      Standard transcriptional
      control elements/factors
    – exonic
• Processing
    – Nucleus. DROSHA, Pre-
      miRNA (~70-mer)
    – Exported to cytoplasm
    – Cytoplasm. DICER, miRNA
      duplex
    – mature miRNA associates
      with RISC
• RISC-miRNA complex binds
  3’UTR of target mRNA
    – inhibition of translation
    – mRNA degradation
    – Deadenylation                 29
      miRNA transcription and translation




Translational
inhibition
                NO…
                          YES!




                        Seed                30
                      sequence
                   miRNA and muscle

miRNAs regulate muscle development, differentiation and disease

  miR       Functions                              Validated target
  miR-1     Inhibition of proliferation            Hand2
            Control of cardiac conductance         lrx5, KCND2
            Myogenesis (Pro-differentiation)       HDAC4
            Cardiogenesis (Pro-differentiation)    Delta
  miR-133   Inhibition of cardiac hypertrophy      RhoA, Cdc-42, WHSC2
            Promotion of proliferation (C and S)   SRF
            Control of cardiac conductance         HERG
  miR-206   Myogenesis                             Cx43
                                                   Fst11, Utrn
                                                   PolA1
  miR-208   β-MHC expression
            Stress-dependent cardiac remodeling    THRAP1

                                                                         31
     miR-1/133 transcriptional control




Thum, T. et al. Cardiovasc Res
2008 79:562-570                          32
miR-1, SRF, Hand2, proliferation: Srivastava, D. 2005
                                 WT   miR-1 overexpressor



             1. miR-1 is                                    3. miR-1
                muscle                                         regulates
                specific                                       prolif.




                  2. SRF
                     regulates                              4. miR-1
                     miR-1                                     regulate
                                                               s Hand2
miR-1/133 in cardiac muscle (paper)




                                      34
THE END!

Questions?

             35