Potential Roles of Arnt2 in Zebrafish Larval Development

Abstract

The aryl hydrocarbon receptor nuclear translocator (ARNT) is a basic helix-loop-helix-PAS heterodimeric transcription factor that dimerizes with other basic helix-loop-helix-PAS proteins to mediate biological responses. The function of ARNT2 is poorly understood. Here we provide an initial characterization of the zebrafish arnt2 null (arnt2 À=À ) mutant to identify functions of Arnt2 during development. Arnt2 À=À mutant zebrafish develop normally until 120 hours postfertilization (hpf ) when morphological changes and functional deficits occur. The C-start escape response initiated by either touch or startle stimuli is absent in the mutants. Brain ventricle size is markedly increased at 120 hpf. Heart ventricles are enlarged, with decreased ventricle wall thickness. A cardiac arrhythmia, characterized by missing beats, is also observed in the mutants. This is associated with bradycardia in arnt2 À=À larvae. Dilated liver sinusoids merge abnormally to form an extensive, labyrinth-like network of vascular channels. External appearance of arnt2 À=À larvae at 120 hpf is indistinguishable from wild type except that the swim bladder is not inflated. The arnt2 À=À mutants are not debilitated when phenotypic effects are first detected at 120 hpf that culminate in mortality, 4 days later around 216 hpf. Gross morphological assessment of the development of forebrain, midbrain, and hindbrain regions, neuromasts and Mauthner neurons, inner ear semicircular canals and otoliths, primary motor neurons, trigeminal ganglia, and trunk skeletal muscles, before or when the arnt2 À=À phenotype was observed, failed to demonstrate a difference from wild type. The only effect in arnt2 À=À larvae that occurred before 120 hpf was a decrease in expression of sim1, an Arnt2 dimerization partner, in the hypothalamus and ventral thalamus at 72 hpf. Further research is needed to determine if the primary functions of Arnt2 occur during the larval stage, when the phenotype is observed, or earlier in development.

Bidirectional crosstalk between Hypoxia-Inducible Factor and glucocorticoid signalling in zebrafish larvae

“…Of note, arnt1 homozygotes, in a vhl /+ or wt background, were morphologically indistinct and adults were viable and fertile. In contrast, the previously published arnt2 -/zebrafish larvae were embryonic lethal around 216 hpf(Hill et al, 2009). Arnt1 and Arnt2 are mutually involved in assuring HIF response in zebrafish:As arnt1;vhl double mutants still activate the phd3:eGFP HIF reporter, we examined the importance of Arnt2 isoform in the HIF response.…”

Association of variants in genes involved in environmental chemical metabolism and risk of cryptorchidism and hypospadias

“…[23][24][25] Arnt2 has pivotal roles in the regulation of early development in zebrafish. 26 ARNT2 polymorphisms have been linked with the risk of some specific congenital malformations in humans such as cleft palate. 27 However, little is known about the relationship of ARNT2 polymorphisms and the risk of MGM.…”

Analysis of postembryonic heart development and maturation in the zebrafish, Danio rerio

“…Significant work has begun to elucidate the mechanisms underlying adult cardiac wound healing and regeneration (reviewed in Major and Poss, 2007). Studies examining aspects of cardiac development and maturation in larval and juvenile zebrafish are limited (Antkiewicz et al, 2006; Hill et al, 2009; Martin and Bartman, 2009; Liu et al; Peshkovsky et al).…”