A novel human heterozygous stat5b variant leads to growth and developmental defects in zebrafish embryos

Abstract

Signal transducer and activator oftranscription 5B (STAT5B) has been identified as a keydownstream mediator of Growth Hormone (GH) signaling insomatic growth. Autosomic recessive human mutations inSTAT5B lead to severe growth retardation associated to immunedysregulation. On the other hand, some heterozygous STAT5Bmutations have been associated to a milder form of the disease.The aim of our study was to evaluate the functionalconsequences of a novel heterozygous human STAT5B variant(K632N), described in a child presenting short stature with mildimmunological dysfunction, during zebrafish embryodevelopment to determine its pathogenicity. To do this, wemicroinjected 100 and 200 pg of wildtype (WT) and mutantmRNA into zebrafish embryos and measured the embryo lengthat 72 hours post fertilization (hpf). In addition, we characterizedthe morphological phenotypes observed in these embryos.Zebrafish embryos microinyected with 100 and 200 pg of mutantmRNA show a dose dependent significant reduction of bodylength at 72 hpf compared to those microinyected with the samedose of WT mRNA (p<0.001) for both 100 and 200 pg. Moreover,the body length is significantly shorter in those embryos injectedwith 200 pg (p<0.001) compared with 100 pg of mutant mRNA.In addition, a significant number of embryos injected withmutant mRNA show developmental defects including pericardialedema, bent spine, and cyclopia compared to those injected withWT mRNA (p<0.01). These morphological phenotypes alsoincrease with the mutant mRNA dose. In conclusion, our studywas able to evidence the pathogenic nature of the STAT5BK632N variant since it leads to growth and developmentaldefects in zebrafish embryos. The zebrafish, and its conservedGH-IGF-I axis, constitutes an ideal in vivo model forcharacterizing the functional effect of genetic variants in orthologhuman genes.