Expression of ADP-ribosylation factor (ARF)-like protein 6 during mouse embryonic development

Abstract

ADP-ribosylation factor (ARF)-like protein 6 (ARL6) is a member of the ARF-like protein (ARL) subfamily of small GTPases (Moss, 1995; Chavrier, 1999). ARLs are highly conserved through evolution and most of them possess the consensus sequence required for GTP binding and hydrolysis (Pasquallato, 2002). Among ARLs, ARL6 which was initially isolated from a J2E erythroleukemic cell line is divergent in its consensus sequences and its expression has been shown to be limited to the brain and kidney in adult mouse (Ingley, 1999). Recently, it was reported that mutations of the ARL6 gene cause type 3 Bardet-Biedl syndrome in humans and that ARL6 is involved in ciliary transport in C. elegans (Chiang, 2004;Fan, 2004). Here, we investigated the expression pattern of ARL6 during early mouse development by whole-mount in situ hybridization and found that interestingly, ARL6 mRNA was localized around the node at 7.0-7.5 days post coitum (dpc) embryos, while weak expression was also found in the ectoderm. At the later stage (8.5 dpc) ARL6 was expressed in the neural plate and probably in the somites. Based on these results, a possible role of ARL6 in early development is discussed in relation to the findings in human and C. elegans (Chiang, 2004;Fan, 2004 (Moss, 1995;Chavrier, 1999). Although ARF-like proteins (ARLs) are very similar to ARFs in amino acid sequences, their biological function remains unclear. ARL1 and ARL3 have recently been shown to be required for localization of GRIP-domain proteins to Golgi membranes (Lowe, 1996;Lu, 2001;Panic, 2003;Setty, 2003). In addition, the expression of ARL4 and ARL5 was found to be developmentally regulated (Lin, 2000;Lin, 2002;Schurmann, 2002). These observations suggest the possibility that the ARL proteins function in membrane traffic which might mediate some developmental processes. ARL6 was first identified in a J2E erythroleukemic cell line. The ARL6 transcript is up-regulated during erythropoietin-induced differentiation of erythroid cells and down-regulated during interleukin-6-induced macrophage differentiation, suggesting a possible role in hemopoietic development (Ingley, 1999). In adult mice, ARL6 shows a tissue-specific expression pattern with the highest expression observed in the brain and kidney. In addition, yeast two-hybrid screening and coimmunoprecipitation reportedly show that ARL6 interacts with the protein-conducting channel subunit SEC61β (Ingley, 1999; Int. J. Dev. Biol. 49: 891-894 (2005) Pettersson, 2000). However, its biological functions remain unclear. Recently, ARL6 was identified as the gene that causes Bardet-Biedl syndrome type 3 (BBS3) (Chiang, 2004;Fan, 2004). Four different homozygous substitutions in the regions including the GTP binding domain in ARL6 were found to be involved in BBS3. BBS3 is a multisystemic disorder characterized by obesity, blindness, polydactyly, renal abnormalities and cognitive impairment. Similar to other BBS's, BBS3 is also thought to result from ciliary dysfunction because loss-of-function mutations ...

Regulation ofFto/Ftmgene expression in mice and humans

“…Thus, a positive feedback loop may exist between Cutl1, Ftm, and SHH signaling. Misregulation of SHH signaling and cilia dysfunction are implicated in obesity, retinal degeneration, right-left asymmetry, renal dysplasia, and polydactyly that characterize the Bardet-Biedl syndrome (10,57,59). Ftm is a basal body protein of cilia that affects SHH signaling (65), suggesting that Ftm may contribute to aspects of hypothalamic development.…”

“…Ftm is a basal body protein of cilia that affects SHH signaling (65), suggesting that Ftm may contribute to aspects of hypothalamic development. Reminiscent of aspects of the Bardet-Biedl syndrome, humans with mutations in RPGRIP, the FTM homolog, develop retinal dysplasia (43,57). Additionally, Cutl1 Ϫ/Ϫ and Fused toes homozygous mutants display left-right asymmetry.…”

Bardet-Biedl syndrome: an emerging pathomechanism of intracellular transport

“…In addition, murine BBS5 and BBS6 was found within brain tissue cells, including the multi-ciliated ependymal cells that line brain ventricles [25,38]. The probable involvement of BBS proteins at the embryonic node, which relies on cilia to specify left-right asymmetry in mammals [57,58], is supported by in situ RNA hybridisation studies that demonstrate the expression of BBS3/ARL6 in the ciliated embryonic node of early mouse embryos [59]. Immunolocalisation studies revealed that mammalian BBS proteins localise at the basal bodies and centrosomes of ciliated cells.…”

Mechanistic insights into Bardet-Biedl syndrome, a model ciliopathy

“…Behavioral abnormalities have been reported in Bbs-knockout mice, but the underlying physical defect has not been explored in detail. Though the exact function of ciliary proteins in brain development is unclear, expression of at least one BBS gene, Bbs3/Arl6, which is involved in ciliary transport (25,116), is seen in developing neural tissues (117). Furthermore, consistent with cerebral anomalies observed in BBS patients (118), the Bbs1-M390R knock-in mouse had several morphological defects in the brain, including ventriculomegaly of the lateral and third ventricles, a thin cerebral cortex, and reduced corpus striatum hippocampus (53).…”