The Glycerol‐3‐Phosphate Acyltransferase TbGAT is Dispensable for Viability and the Synthesis of Glycerolipids in Trypanosoma brucei

Glycerolipids are the main constituents of biological membranes in Trypanosoma brucei, which causes sleeping sickness in humans. Importantly, they occur as a structural component of the glycosylphosphatidylinositol lipid anchor of the abundant cell surface glycoproteins procyclin in procyclic forms and variant surface glycoprotein in bloodstream form, that play crucial roles for the development of the parasite in the insect vector and the mammalian host, respectively. The present work reports the characterization of the glycerol‐3‐phosphate acyltransferase TbGAT that initiates the biosynthesis of ester glycerolipids. TbGAT restored glycerol‐3‐phosphate acyltransferase activity when expressed in a Leishmania major deletion strain lacking this activity and exhibited preference for medium length, unsaturated fatty acyl‐CoAs. TbGAT localized to the endoplasmic reticulum membrane with its N‐terminal domain facing the cytosol. Despite that a TbGAT null mutant in T. brucei procyclic forms lacked glycerol‐3‐phosphate acyltransferase activity, it remained viable and exhibited similar growth rate as the wild type. TbGAT was dispensable for the biosynthesis of phosphatidylcholine, phosphatidylinositol, phosphatidylserine, and GPI‐anchored protein procyclin. However, the null mutant exhibited a slight decrease in phosphatidylethanolamine biosynthesis that was compensated with a modest increase in production of ether phosphatidylcholine. Our data suggest that an alternative initial acyltransferase takes over TbGAT's function in its absence.     

Effects of Undernutrition and Thyroid State on the Ontogenetic Changes of D1, D2, and D3 Brain-Specific Proteins in Rat Cerebellum

Abstract: Disturbances in metabolic balance brought about by alterations in thyroid state and undernutrition during early life had a marked effect on the concentrations of the brain-specific proteins, D1, D2, and D3 in the developing rat cerebellum. In normal rats, the concentrations of D1 and D3 increased and that of D2 decreased during the first 3 weeks after birth. In the hyperthyroid state a small but consistent advancement was observed in the developmental curves of these proteins. The hypothyroid state caused a marked retardation in the maturational pattern of D1 and D2 but not of D3. In undernutrition, at 6 days the concentrations of D1 and D3 proteins were higher than in controls, but thereafter the developmental increase was markedly delayed for D1 only. The concentration of D2 was normal at 6 days, but after the first week a marked retardation was observed in the maturational pattern of this protein in undernourished rats. In addition, the "anodic-immature"form of D2 predominated in 6-day-old controls, but this was gradually replaced by a "cathodic-mature"form which progressively became the dominant form of D2 in 35-day-old rat cerebellum. The developmental switch in terms of the two forms was also advanced in hyperthyroidism and retarded in thyroid deficiency and undernutrition. Furthermore, daily treatment of hypothyroid rats with physiological doses of thyroxine from birth restored the concentrations of D1 and D2 to normal, but that of D3 was increased above control levels, indicating differences between the proteins in their sensitivity to mechanisms of control by thyroid hormone. Also, the overall effects of undernutrition were markedly different from those of hypothyroidism.     

Effect of methylmalonate on ketone body metabolism in developing rat brain

The oxidation of 3-hydroxy[3-¹⁴C]butyrate to CO₂ and its incorporation into cerebral lipids by cortex slices from one-week old rats were markedly inhibited by methylmalonate. However, methylmalonate had no effect on the metabolism of labelled aceto- acetate, glucose and acetate by brain slices. Addition of propionate in the incubation medium reduced cerebral lipogenesis from labelled 3-hydroxybutyrate and acetate. Acute methylmalonic acidemia induced in one-week old pups by injecting 3% methylmalonate solution caused a reduction in the incorporation of labelled 3-hydroxybutyrate into cerebral lipids. However, acute methylmalonic acidemia had no effect on cerebral lipogensis $\text{in vivo}$ from labelled acetate. These findings show (i) the conversion of 3-hydroxybutyrate to acetoacetate by 3-hydroxybutyrate dehydrogenase in the brain is inhibited by methylmalonate, and (ii) an inhibition of cerebral lipid synthesis by propionate, which also accumulates in patients with methylmalonic aciduria.     

Role of Sertoli cells in injury-associated testicular germ cell apoptosis

This review examines experimental models of Sertoli cell injury resulting in germ cell apoptosis. Since germ cells exist in an environment created by Sertoli cells, paracrine signaling between these intimately associated cells must regulate the process of germ cell death. Germ cell apoptosis may be signaled by a decrease in Sertoli cell pro-survival factors, an increase in Sertoli cell pro-apoptotic factors, or both. The different models of Sertoli cell injury indicate that spermatogenesis is susceptible to disruption, and that targeting critical Sertoli cell functions can lead to rapid and massive germ cell death.     

The tardigrade Hypsibius dujardini, a new model for studying the evolution of development

Studying development in diverse taxa can address a central issue in evolutionary biology: how morphological diversity arises through the evolution of developmental mechanisms. Two of the best-studied developmental model organisms, the arthropod Drosophila and the nematode Caenorhabditis elegans, have been found to belong to a single protostome superclade, the Ecdysozoa. This finding suggests that a closely related ecdysozoan phylum could serve as a valuable model for studying how developmental mechanisms evolve in ways that can produce diverse body plans. Tardigrades, also called water bears, make up a phylum of microscopic ecdysozoan animals. Tardigrades share many characteristics with C. elegans and Drosophila that could make them useful laboratory models, but long-term culturing of tardigrades historically has been a challenge, and there have been few studies of tardigrade development. Here, we show that the tardigrade Hypsibius dujardini can be cultured continuously for decades and can be cryopreserved. We report that H. dujardini has a compact genome, a little smaller than that of C. elegans or Drosophila, and that sequence evolution has occurred at a typical rate. H. dujardini has a short generation time, 13–14 days at room temperature. We have found that the embryos of H. dujardini have a stereotyped cleavage pattern with asymmetric cell divisions, nuclear migrations, and cell migrations occurring in reproducible patterns. We present a cell lineage of the early embryo and an embryonic staging series. We expect that these data can serve as a platform for using H. dujardini as a model for studying the evolution of developmental mechanisms.     

Overexpression of extracellular superoxide dismutase has a protective role against hyperoxia-induced brain injury in neonatal mice

There is increasing evidence that hyperoxia, particularly at the time of birth, may result in neurological injury, in particular to the susceptible vasculature of these tissues. This study was aimed at determining whether overexpression of extracellular superoxide dismutase (EC-SOD) is protective against brain injury induced by hyperoxia. Transgenic (TG) mice (with an extra copy of the human extracellular superoxide dismutase gene) and wild-type (WT) neonate mice were exposed to hyperoxia (95% of F(i) o(2) ) for 7 days after birth versus the control group in room air. Brain positron emission tomography (PET) scanning with fludeoxyglucose (FDG) isotope uptake was performed after exposure. To assess apoptosis induced by hyperoxia exposure, caspase 3 ELISA and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining were performed. Quantitative western blot for the following inflammatory markers was performed: glial fibrillary acidic protein, ionized calcium-binding adaptor molecule 1, macrophage-inhibiting factor, and phospho-AMP-activated protein kinase. PET scanning with FDG isotope uptake showed significantly higher uptake in the WT hyperoxia neonate brain group (0.14 ± 0.03) than in both the TG group (0.09 ± 0.01) and the control group (0.08 ± 0.02) (P< 0.05). Histopathological investigation showed more apoptosis and dead neurons in hippocampus and cerebellum brain sections of WT neonate mice after exposure to hyperoxia than in TG mice; this finding was also confirmed by TUNEL staining. The caspase 3 assay confirmed the finding of more apoptosis in WT hyperoxia neonates (0.814 ± 0.112) than in the TG hyperoxic group (0.579 ± 0.144) (P < 0.05); this finding was also confirmed by TUNEL staining. Quantitative western blotting for the inflammatory and metabolic markers showed significantly higher expression in the WT group than in the TG and control groups. Thus, overexpression of EC-SOD in the neonate brain offers significant protection against hyperoxia-induced brain damage.     

The functional relationship between ectodermal and mesodermal segmentation in the crustacean, Parhyale hawaiensis

In arthropods, annelids and chordates, segmentation of the body axis encompasses both ectodermal and mesodermal derivatives. In vertebrates, trunk mesoderm segments autonomously and induces segmental arrangement of the ectoderm-derived nervous system. In contrast, in the arthropod Drosophila melanogaster, the ectoderm segments autonomously and mesoderm segmentation is at least partially dependent on the ectoderm. While segmentation has been proposed to be a feature of the common ancestor of vertebrates and arthropods, considering vertebrates and Drosophila alone, it is impossible to conclude whether the ancestral primary segmented tissue was the ectoderm or the mesoderm. Furthermore, much of Drosophila segmentation occurs before gastrulation and thus may not accurately represent the mechanisms of segmentation in all arthropods. To better understand the relationship between segmented germ layers in arthropods, we asked whether segmentation is an intrinsic property of the ectoderm and/or the mesoderm in the crustacean Parhyale hawaiensis by ablating either the ectoderm or the mesoderm and then assaying for segmentation in the remaining tissue layer. We found that the ectoderm segments autonomously. However, mesoderm segmentation requires at least a permissive signal from the ectoderm. Although mesodermal stem cells undergo normal rounds of division in the absence of ectoderm, they do not migrate properly in respect to migration direction and distance. In addition, their progeny neither divide nor express the mesoderm segmentation markers Ph-twist and Ph-Even-skipped. As segmentation is ectoderm-dependent in both Parhyale and holometabola insects, we hypothesize that segmentation is primarily a property of the ectoderm in pancrustacea.