Bdnf knockdown in zebrafish larvae leads to pericardial oedema formation, impaired glomerular filtration and down‐regulation of podocyte‐specific genes. Bdnf morpholinos (bdnfMO) and control morpholinos (CtrlMO) were injected in ET zebrafish eggs. Brightfield pictures were taken 3 dpf (A; a and b) and 6 dpf (A; e and f). bdnfMO‐injected larvae exhibit a higher rate of pericardial oedema development and a lower viability than normal controls (B). Morpholino injection in CADE larvae reveals an impairment of glomerular filtration barrier function in bdnfMO‐injected larvae 3 dpf (A; c) and 6 dpf (A; g) compared to CtrlMO‐injected larvae (A; d and f). The knockdown of bdnf was verified by RT‐PCR (C). The down‐regulation of the podocyte marker nphs2 was verified on the mRNA level by RT‐PCR (C) and qRT‐PCR (D). Expression levels were normalized to zgc:158463 in RT‐PCR and to zgc:158463 and eef1a1/1 in qRT‐PCR by the ΔΔCt method. [Scale bars = 500 μm] [*P < .05, ***P < .001]

Bdnf knockdown in zebrafish larvae leads to morphological changes in the glomerulus and the down‐regulation of podocyte marker proteins. BdnfMO and CtrlMO were injected in ET eggs expressing eGFP specifically in podocytes. Cryosections were counterstained for F‐actin by phalloidine (red) and nuclei by Hoechst (blue) (A; a‐h). bdnfMO‐treated larvae show an enlarged glomerular tuft (A; b arrow) and Bowman's space (A; b asterisk) compared with the normal morphology of the CtrlMO‐treated larvae (A; e‐h). Counterstaining of the slit diaphragm protein nephrin (red) and nuclei by Hoechst (blue, A; i‐p) reveals a down‐regulation of nephrin due to bdnfMO treatment (A; k) compared to CtrlMO‐treated larvae (A; o). [Scale bars = 20 μm] In vivo microscopy reveals 2 different phenotypes of bdnfMO‐treated larvae. Phenotype 1 is characterized by unfused glomeruli (B; a white line and b), a reduced number of podocytes and a dilatation of Bowman's space and the glomerular tuft (B; a asterisks). The second phenotype is characterized by the absence of podocyte major processes, a reduced podocyte number and a dilatation of Bowman's space and the glomerular tuft (B; c asterisk and d). CtrlMO‐injected larvae show a normal glomerular morphology with well‐shaped major processes (B; e and f). [Scale bars = 20 μm]