title: Induction of apoptosis and inhibition of cell growth by tbx5 knockdown contribute to dysmorphogenesis in Zebrafish embryos.
abstract: BACKGROUND
  The tbx5 mutation in human causes Holt-Oram syndrome, an autosomal dominant condition characterized by a familial history of congenital heart defects and preaxial radial upper-limb defects. We report aberrant apoptosis and dormant cell growth over head, heart, trunk, fin, and tail of zebrafish embryos with tbx5 deficiency correspond to the dysmorphogenesis of tbx5 morphants.
  
  
  METHODS
  Wild-type zebrafish embryos at the 1-cell stage were injected with 4.3 nl of 19.4 ng of tbx5 morpholino or mismatch-tbx5-MO respectively in tbx5 morphants and mismatched control group. Semi-quantitative RT-PCR was used to for expression analysis of apoptosis and cell cycle-related genes. TUNEL and immunohistochemical assay showed the apoptosis spots within the local tissues. Ultra-structure of cardiac myocardium was examined by transmission electron microscope.
  
  
  RESULTS
  Apoptosis-related genes (bad, bax, and bcl2), and cell cycle-related genes (cdk2, pcna, p27, and p57) showed remarkable increases in transcriptional level by RT-PCR. Using a TUNEL and immnuohistochemical assay, apoptosis was observed in the organs including the head, heart, pectoral fins, trunk, and tail of tbx5 knockdown embryos. Under transmission electron microscopic examination, mitochondria in cardiomyocytes became swollen and the myocardium was largely disorganized with a disarrayed appearance, compatible with reduced enhancement of myosin in the cardiac wall. The ATP level was reduced, and the ADP/ATP ratio as an apoptotic index significantly increased in the tbx5 deficient embryos.
  
  
  CONCLUSIONS
  Our study highlighted that tbx5 deficiency evoked apoptosis, distributed on multiple organs corresponding to dysmorphogenesis with the shortage of promising maturation, in tbx5 knockdown zebrafish embryos. We hypothesized that mesenchymal cell apoptosis associated with altered TBX5 level may subsequently interfered with organogenesis and contributed to dysmorphogenesis in tbx5 deficiency zebrafish embryos.
authors: Department of Pediatrics and Pathology, Taipei Veterans General Hospital, Taipei, Taiwan. jenherlu@gmail.com
authors: Jenher
authors: J
authors: Lu
authors: Tzuchun
authors: T
authors: Tsai
authors: Sielin
authors: S
authors: Choo
authors: Shuyu
authors: S
authors: Yeh
authors: Renbing
authors: R
authors: Tang
authors: Anhang
authors: A
authors: Yang
authors: Hsinyu
authors: H
authors: Lee
authors: Jennkan
authors: J
authors: Lu
mesh_terms: D000255:Adenosine Triphosphate / Q000032:analysis; D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D002453:Cell Cycle / Q000235:genetics*; D047108:Embryonic Development / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D008648:Mesoderm / Q000166:cytology; D009024:Morphogenesis / Q000235:genetics*; D009206:Myocardium / Q000648:ultrastructure; D020825:T-Box Domain Proteins / Q000235:genetics* / Q000378:metabolism; D015027:Zebrafish / Q000002:abnormalities* / Q000235:genetics
chemical_list: D020825:T-Box Domain Proteins; C103172:T-box transcription factor 5; D000255:Adenosine Triphosphate