Glycerol phosphate dehydrogenase in developing chick retina and brain

Glutamine catabolism supports amino acid biosynthesis and suppresses the integrated stress response to promote photoreceptor survival

Photoreceptor loss results in vision loss in many blinding diseases, and metabolic dysfunction underlies photoreceptor degeneration. So, exploiting photoreceptor metabolism is an attractive strategy to prevent vision loss. Yet, the metabolic pathways that maintain photoreceptor health remain largely unknown. Here, we investigated the dependence of photoreceptors on Gln catabolism. Gln is converted to glutamate via glutaminase (GLS), so mice lacking GLS in rod photoreceptors were generated to inhibit Gln catabolism. Loss of GLS produced rapid rod photoreceptor degeneration. In vivo metabolomic methodologies and metabolic supplementation identified Gln catabolism as critical for glutamate and aspartate biosynthesis. Concordant with this amino acid deprivation, the integrated stress response (ISR) was activated with protein synthesis attenuation, and inhibiting the ISR delayed photoreceptor loss. Furthermore, supplementing asparagine, which is synthesized from aspartate, delayed photoreceptor degeneration. Hence, Gln catabolism is integral to photoreceptor health, and these data reveal a novel metabolic axis in these metabolically-demanding neurons.

Microarray-based analysis of early development in Xenopus laevis

In order to examine transcriptional regulation globally, during early vertebrate embryonic development, we have prepared Xenopus laevis cDNA microarrays. These prototype embryonic arrays contain 864 sequenced gastrula cDNA. In order to analyze and store array data, a microarray analysis pipeline was developed and integrated with sequence analysis and annotation tools. In three independent experimental settings, we demonstrate the power of these global approaches and provide optimized protocols for their application to molecular embryology. In the first set, by comparing maternal versus zygotic transcription, we document groups of genes that are temporally regulated. This analytical approach resulted in the discovery of novel temporally regulated genes. In the second, we examine changes in gene expression spatially during development by comparing dorsal and ventral mesoderm dissected from early gastrula embryos. We have discovered novel genes with spatial enrichment from these experiments. Finally, we use the prototype microarray to examine transcriptional responses from embryonic explants treated with activin. We selected genes (two of which are novel) regulated by activin for further characterization. All results obtained by the arrays were independently tested by RT-PCR or by in situ hybridization to provide a direct assessment of the accuracy and reproducibility of these approaches in the context of molecular embryology.

Regional protein patterns of the embryonic chick brain: developmental shifts and the effects of light stimulation

The developmental changes in the regional protein patterns of the embryonic brain of chick were analysed by micro-two-dimensional polyacrylamide gel electrophoresis stained by a highly sensitive procedure with Coomassie Brilliant Blue G-250 that completely avoids background staining. More than 400 protein spots were resolved in a computerized plot. Many proteins of the various embryonic brain regions varied with age. At least six of these proteins changed remarkably during development. One of them (Mr 14K) was prominent at 6 days and disappeared after 12 days of incubation. One acidic protein (Mr 30K) appeared at 12 days together with two acidic protein spots near tubulin and increased with development. A group of more basic proteins (Mr 94K) was prominent at 6 day incubation and decreased during development. One more basic protein (Mr 20K) was first observed at 18 days of incubation in the metencephalon. It was identified as myelin basic protein, and strikingly increased in all brain regions until hatching. A group of basic proteins with high molecular weight (Mr 94K) appeared at day 12 of incubation, and increased remarkably before hatching. They were identified to be collagen associated with brain capillary vessels. Stimulation by intermittent light in ovo from day 10 to day 16 caused a retarded appearance of these collagen proteins, and an increased formation of tubulin in the optic lobe of the developing chick embryo.

Glycerol phosphate dehydrogenase activity of oligodendrocytes isolated from adult pig brain: its inducibility by hydrocortisone

Developing oligodendrocytes cultured in vitro express glycerol phosphate dehydrogenase (GPDH; EC 1.1.1.8) and are known to respond to glucocorticoid treatment by increased activity of GPDH. We present evidence that GPDH is enriched in white matter and oligodendrocytes of adult pig brain. Bulk-isolated oligodendrocytes maintained in culture for several weeks exhibit an almost constant level of GPDH activity. Furthermore, a 4-day stimulation with hydrocortisone induces GPDH specific activity of long-term cultured oligodendrocytes from adult pig brain.

Lipids of nervous tissue: composition and metabolism

As indicated in the Introduction, the many significant developments in the recent past in our knowledge of the lipids of the nervous system have been collated in this article. That there is a sustained interest in this field is evident from the rather long bibliography which is itself selective. Obviously, it is not possible to summarize a review in which the chemistry, distribution and metabolism of a great variety of lipids have been discussed. However, from the progress of research, some general conclusions may be drawn. The period of discovery of new lipids in the nervous system appears to be over. All the major lipid components have been discovered and a great deal is now known about their structure and metabolism. Analytical data on the lipid composition of the CNS are available for a number of species and such data on the major areas of the brain are also at hand but information on the various subregions is meagre. Such investigations may yet provide clues to the role of lipids in brain function. Compared to CNS, information on PNS is less adequate. Further research on PNS would be worthwhile as it is amenable for experimental manipulation and complex mechanisms such as myelination can be investigated in this tissue. There are reports correlating lipid constituents with the increased complexity in the organization of the nervous system during evolution. This line of investigation may prove useful. The basic aim of research on the lipids of the nervous tissue is to unravel their functional significance. Most of the hydrophobic moieties of the nervous tissue lipids are comprised of very long chain, highly unsaturated and in some cases hydroxylated residues, and recent studies have shown that each lipid class contains characteristic molecular species. Their contribution to the properties of neural membranes such as excitability remains to be elucidated. Similarly, a large proportion of the phospholipid molecules in the myelin membrane are ethanolamine plasmalogens and their importance in this membrane is not known. It is firmly established that phosphatidylinositol and possibly polyphosphoinositides are involved with events at the synapse during impulse propagation, but their precise role in molecular terms is not clear. Gangliosides, with their structural complexity and amphipathic nature, have been implicated in a number of biological events which include cellular recognition and acting as adjuncts at receptor sites. More recently, growth promoting and neuritogenic functions have been ascribed to gangliosides. These interesting properties of gangliosides wIll undoubtedly attract greater attention in the future.(ABSTRACT TRUNCATED AT 400 WORDS)

Glycerol phosphate dehydrogenase in developing retina of normal and mutant mice

The specific activity of glycerol phosphate dehydrogenase (GPDH; E.C. 1.1.1.8) was determined in the retinas of C57BL/6J mice from 2 to 45 days after birth. Comparisons were made with age-matched mice congenic to C57BL/6J and homozygous for the autosomal recessive mutations for retinal degeneration (rd) and light ear (le). The total activity of GPDH in the developing retina was similar in each strain throughout development. However, following the loss of photoreceptor cells in the rdle mice, the specific activity of GPDH increased to approximately twice the level of that in the controls. These data suggest that GPDH is absent from the photoreceptor cells and that its expression in the remaining retinal cells is unaffected by the loss of the photoreceptor cells. Retinal GPDH does not exhibit the eight-to ten-fold increase seen during development of the brain, but instead remains essentially constant during this time period, and in adult animals the specific activity of GPDH in the retina is about 20-fold less than it is in the brain. Neither mouse retinal GPDH nor brain GPDH is affected by adrenalectomy, suggesting that they are not regulated by glucocorticoids. The major form of GPDH in the retina is distinct from the major form in mouse brain since immunotitration experiments demonstrated that 70-80% of retinal GPDH does not react with anti-GPDH IgG, whereas the reverse was true for the brain enzyme.

Analysis of a distinctive protein in chick retina during development

Soluble proteins from the chick retina were analyzed at various developmental stages by SDS-polyacrylamide gel electrophoresis. A peptide of about 24,000 daltons (24 Kd protein) appeared in the 14-day embryo and gradually increased with embryonic age, maintaining a fairly steady level after hatching. Polypeptides which correspond to actin and tubulin, however, remained almost unchanged during development. The 24 Kd protein was not detected in the cerebrum, tectum, pigment epithelium or vitreous body at any age. To characterize this protein, it was partially purified by gel filtration and ion exchange column chromatography, and its isoelectric point was measured. It was focused in a diffuse spot at about pH 5.5. In the bovine retina, a protein was observed at 24,000 daltons on SDS-polyacrylamide gel, but its isoelectric point was more basic than that of chick retina. It is suggested that the 24 Kd protein is one of the distinctive proteins that increase in concentration during the chick retinal development, and would be closely associated with retinal functions.