Pdlim7 (LMP4) regulation of Tbx5 specifies zebrafish heart atrio-ventricular boundary and valve formation

Abstract

Tbx5 is involved in congenital heart disease, however, the mechanisms leading to organ malformation are greatly unknown. We hypothesized a model by which the Tbx5 binding protein Pdlim7 controls nuclear/cytoplasmic shuttling and function of the transcription factor. Using the zebrafish, we present in vivo significance for an essential role of Tbx5/Pdlim7 protein interaction in the regulation of cardiac formation. Knock-down of Pdlim7 results in a non-looped heart, strikingly reminiscent of the tbx5 heartstrings mutant phenotype. However, while misregulation of Pdlim7 and Tbx5 produce similar aberrant cardiac morphology, molecular and histological analysis uncovered that the Pdlim7 and Tbx5 cardiac phenotypes are due to opposite effects on valve development. Loss of Pdlim7 function causes no valve tissue to develop while lack of Tbx5 results in increased valve tissue. These opposing defects are evident before valve formation and are the result of distinct gene misregulation during specification of the atrio-ventricular (AV) boundary. We show that Pdlim7/Tbx5 interactions affect the expression of Tbx5 target genes nppa and tbx2b at the AV boundary, and their domains of misexpression directly correlate with the identified valve defects. These studies demonstrate that controlling the correct balance of Tbx5 activity is crucial for the specification of the AV boundary and valve formation.

Transmembrane protein 2 (Tmem2) is required to regionally restrict atrioventricular canal boundary and endocardial cushion development

“…The expanded AVC phenotype of wkm mutants is phenotypically indistinguishable from the defect seen in zebrafish tbx5, apc and hey2 mutants. In these cases, an expansion of bmp4 expression throughout the ventricular myocardium is observed and is associated with EC marker expansion (Camarata et al, 2010;Garrity et al, 2002;Hurlstone et al, 2003;Rutenberg et al, 2006). Here, we show that, downstream of tmem2, ectopic bmp4 expression is functionally responsible for the expansion of the immature AVC.…”

“…Mutants for genes such as ugdh (jekyll) (Walsh and Stainier, 2001), notch1 (Timmerman et al, 2004) and foxn4 (slipjig) (Chi et al, 2008) exhibit a loss or diminution of EC development. By contrast, mutations in apc (Hurlstone et al, 2003), tbx5 (heartstrings) (Camarata et al, 2010;Garrity et al, 2002) or hey2 (gridlock) (Rutenberg et al, 2006) result in an expansion of the AVC. In this latter category of mutants, the AVC-chamber boundary is compromised.…”

Evidence of an Association between Age-Related Functional Modifications and Pathophysiological Changes in Zebrafish Heart

“…Recently, mutations that affect atrial and ventricular development have been reported [10,11,12]. Embryonic and postembryonic cardiac development [13,14] and adult zebrafish electrocardiogram (ECG) [15] have been described.…”

Kctd10 regulates heart morphogenesis by repressing the transcriptional activity of Tbx5a in zebrafish

“…This protein synergistically acts with Tbx20, BMP4, GATA4, Nkx2-5 and other factors to regulate the expression of many chamber-specific genes 8,14,20 . It also restricts the expression of Tbx2 (tbx2b in zebrafish) and has2 (hyaluronan synthase 2) at the AVC to facilitate the formation of the endocardial cushion and valve 21 .…”