Essential role of RGS-PX1/sorting nexin 13 in mouse development and regulation of endocytosis dynamics

Abstract

RGS-PX1 (also known as sorting nexin 13) is a member of both the regulator of G protein signaling (RGS) and sorting nexin (SNX) protein families. Biochemical and cell culture studies have shown that RGS-PX1͞SNX13 attenuates G␣s-mediated signaling through its RGS domain and regulates endocytic trafficking and degradation of the epidermal growth factor receptor. To understand the functions of RGS-PX1͞SNX13 in vivo, we generated mice carrying targeted mutations of Snx13 and found that systemic Snx13-null mice were embryonic lethal around midgestation. Snx13-null embryos had significant overall growth retardation and defects in neural tube closure, blood vessel formation, and the formation of the placental labyrinthine layer. Moreover, the Snx13-null visceral yolk sac endoderm cells showed dramatic changes in the organization of endocytic compartments, abundant autophagic vacuoles, and abnormal localization of several endocytic markers, including megalin, a receptor for nutrients and proteins; ARH, a coat protein that binds megalin; LAMP2; and LC3. These changes suggest that Snx13-null embryos are defective in nutrient uptake and transport, which may contribute to the other developmental abnormalities observed. Taken together, our findings demonstrate an essential role for RGS-PX1͞SNX13 in mouse development and provide previously undescribed insights into its cellular function in the regulation of endocytosis dynamics.megalin ͉ receptor endocytosis ͉ regulator of G protein signaling ͉ visceral yolk sac endoderm R eceptor-mediated endocytosis is the process by which plasma membrane components and extracellular materials such as nutrients, hormones, antigens, and other macromolecules are selectively internalized into cytoplasmic vesicles, delivered to early and late endosomes and degraded in lysosomes or recycled back to the plasma membrane through recycling endosomes (1-3). Trafficking between these endocytic compartments is highly regulated and often involves critical sorting steps. Recently, a large family of sorting nexin (SNX) proteins characterized by the presence of Phox (PX) domains has been identified and implicated in the regulation of different steps of the endocytic pathway (4, 5). For example, the founding member of the SNX family, SNX1, was identified as an interacting partner of the epidermal growth factor receptor, and overexpression of SNX1 was found to enhance lysosomal degradation of epidermal growth factor receptor (6). More recently, knock-down of SNX1 expression by RNA interference was shown to perturb the steady state distribution of the cation-independent mannose-6-phosphate receptor (CI-MPR) from the trans-Golgi network to endosomes and to increase the degradation rate of CI-MPR, establishing a role for SNX1 in endosome-to-trans-Golgi network transport (7).RGS-PX1 (also known as SNX 13, the designation by the human gene nomenclature committee) was identified originally as a member of the regulator of G protein signaling (RGS) protein family through bioinformatics analysis (8). RGS-PX1 contains...

Delivery of endosomes to lysosomes via microautophagy in the visceral endoderm of mouse embryos

“…This endosomal function as a signalling centre has been shown for various ligand-receptor systems, including Wnt, transforming growth factor-β, BMP and fibroblast growth factor, which have central roles in embryonic patterning. Mutations affecting the early stages of the endocytic pathway caused various developmental abnormalities 43,44 . In contrast to these promoting roles of the early endosomes in the signal transduction, the late stages of the endocytic pathway can terminate signalling events by separating the activated receptors from cytosolic transducers.…”

SLIC‐1/sorting nexin 20: A novel sorting nexin that directs subcellular distribution of PSGL‐1

“…Despite a vast number of reports on sorting nexins in recent years, gene deletion in mice has not been applied extensively to study sorting nexins, and up to date only three sorting nexins (i.e. SNX1, SNX2, and SNX13) have been deleted from the mouse genome [57,58].…”

A SNX10/V-ATPase pathway regulates ciliogenesis in vitro and in vivo

“…The double knockout mice die at midgestation, which complicates the detailed analysis of the in vivo functions of SNX1 and 2 [17]. SNX13-knockout mice are also embryonic lethal [18], while SNX27 regulates the postnatal growth and survival in the mouse model [19]. So, despite the initial interests in their roles in signal transduction (mainly on the trafficking of membrane receptors), the biological functions of SNX genes remain largely unknown.…”