D-3-Phosphoglyceratedehydrogenase (Phgdh; EC 1.1.1.95) is the first committed enzyme of L-serine biosynthesis in the phosphorylated pathway. To determine the physiological importance of Phgdh-dependent L-serine biosynthesis in vivo, we generated Phgdh-deficient mice using targeted gene disruption in embryonic stem cells. The absence of Phgdh led to a drastic reduction of Lserine metabolites such as phosphatidyl-L-serine and sphingolipids. Phgdh null embryos have small bodies with abnormalities in selected tissues and died after days post-coitum 13.5. Striking abnormalities were evident in the central nervous system in which the Phgdh null mutation culminated in hypoplasia of the telencephalon, diencephalon, and mesencephalon; in particular, the olfactory bulbs, ganglionic eminence, and cerebellum appeared as indistinct structures. These observations demonstrate that the Phgdh-dependent phosphorylated pathway is essential for normal embryonic development, especially for brain morphogenesis.

After transplantation, adult bone marrow-derived mesenchymal stem cells (BM-MSCs) may undergo transdifferentiation and/or cell fusion in response to new environments. However, the mechanism(s) that govern these cell fate switches remain unknown. Here we demonstrate that the pathology associated with murine Niemann-Pick disease type C (NP-C) cerebellum augments the ability of BM-MSCs to fuse with Purkinje neurons. The results suggest that the degenerative microenvironment of Purkinje neurons in the NP-C cerebellum modulates the cell fate switch of BM-MSCs via cell fusion.

We previously found that phosphatidylglucoside (PtdGlc), a novel glycolipid expressed in HL60 cells, plays a role in forming signaling microdomains involved in cellular differentiation. Because cells contain minute levels of PtdGlc, pure PtdGlc is very difficult to isolate. Thus, its complete structure has never been assessed. To aid in analyzing PtdGlc, we generated a PtdGlc-specific monoclonal antibody, DIM21, by immunizing mice with detergent-insoluble membranes isolated from HL60 cells [Yamazaki, Y., et al. (2006) J. Immunol. Methods 311, 106-116]. DIM21 immunostaining of murine CNS tissues revealed stage- and cell type-specific localization of the DIM21 antigen during development, with especially high levels of expression in radial glia/astroglia. DIM21 immunostained cultured hippocampal astroglia in a punctate fashion. To characterize the structure of PtdGlc, we isolated DIM21 antigen from fetal brains. Using successive column chromatography, we purified two previously unrecognized glycolipids, PGX-1 and PGX-2, from embryonic day 21 rat brains. DIM21 reacted more strongly to PGX-2 than to PGX-1. Structural analyses with 600 MHz (1)H NMR, FT-ICR mass spectrometry, and GC revealed that PGX-1 is phosphatidyl beta-d-(6-O-acetyl)glucopyranoside and PGX-2 is phosphatidyl beta-d-glucopyranoside. The yields of PGX-1 and PGX-2 were approximately 250 +/- 150 and 440 +/- 270 nmol/g of dried brains, respectively. Surprisingly, both glycolipids were composed exclusively of C18:0 at the C1 position and C20:0 at the C2 position of the glycerol backbone. This saturated fatty acyl chain composition comprising a single molecular species rarely occurs in known mammalian lipids and provides a molecular basis for why PtdGlc resides in raftlike lipid microdomains.

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