sept7b is essential for pronephric function and development of left–right asymmetry in zebrafish embryogenesis

Abstract

The conserved septin family of filamentous small GTPases plays important roles in mitosis, cell migration and cell morphogenesis by forming scaffolds and diffusion barriers. Recent studies in cultured cells in vitro indicate that a septin complex of septin 2, 7 and 9 is required for ciliogenesis and cilia function, but septin function in ciliogenesis in vertebrate organs in vivo is not understood. We show that sept7b is expressed in ciliated cells in different tissues during early zebrafish development. Knockdown of sept7b by using morpholino antisense oligonucleotides caused misorientation of basal bodies and cilia, reduction of apical actin and the shortening of motile cilia in Kupffer's vesicle and pronephric tubules. This resulted in pericardial and yolk sac edema, body axis curvature and hydrocephaly. Notably, in sept7b morphants we detected strong leftright asymmetry defects in the heart and lateral plate mesoderm (situs inversus), reduced fluid flow in the kidney, the formation of kidney cysts and loss of glomerular filtration barrier function. Thus, sept7b is essential during zebrafish development for pronephric function and ciliogenesis, and loss of expression of sept7b results in defects that resemble human ciliopathies.

Septins in kidney: A territory little explored

“…kidney. sept6 mRNA and Septin 7 protein were found to be expressed in the pronephros (shown for Septin 7 in Figure 3a-c) and other ciliated organs in larval zebrafish (Dash et al, 2014;Zhai et al, 2014).…”

“…In human kidney, SEPT2 has been shown to localize to glomeruli . In cultured inner medullary collecting duct (IMCD3) cells, SEPT2 and SEPT7 have been shown to localize at the base of the cilia (shown for SEPT7 in Figure 3d-f ) as well as in a vesicular pattern in the cytoplasm (Dash et al, 2014;Hu et al, 2010). In epithelial MDCK cells, SEPT2 fibers colocalize with polyglutamylated microtubules near the trans-Golgi network sites of apical and basolateral protein export (Spiliotis, Hunt, Hu, Kinoshita, & Nelson, 2008).…”

“…Confocal microscopy analysis indicated the presence of Septin 7 in both the cytoplasm and at the base and along the cilia in pronephric duct cells (Dash et al, 2014). Morpholino antisense oligonucleotidemediated knockdown of either sept6 or sept7b led to body axis curvature and also pericardial edema and pronephric cyst formation (shown for sept7b in Figure 4a,b), both signs of defective pronephric function (Drummond et al, 1998).…”

“…In mouse and zebrafish kidney, Septin 7 localizes to both glomeruli and tubules (shown for zebrafish in Figure 3a-c) (Dash et al, 2014;Wasik et al, 2012). In human kidney, SEPT2 has been shown to localize to glomeruli .…”

“…Morpholino antisense oligonucleotidemediated knockdown of either sept6 or sept7b led to body axis curvature and also pericardial edema and pronephric cyst formation (shown for sept7b in Figure 4a,b), both signs of defective pronephric function (Drummond et al, 1998). (Figure 4c-g) without affecting the normal 9 + 2 organization of the microtubules in the axoneme of the cilia (Dash et al, 2014). This led to aberrant and slow beating of the cilia and defects in fluid flow, reducing the kidney function (Dash et al, 2014).…”