Effect of D-serine on spermatogenesis and extracellular signal-regulated protein kinase (ERK) phosphorylation in the testis of the silkworm, Bombyx mori

Physiology, Pathophysiology and Clinical Relevance of D-Amino Acids Dynamics: From Neurochemistry to Pharmacotherapy

Over three decades ago, two independent groups of investigators identified free D-aspartic and later D-serine in specific brain nuclei and endocrine glands. This finding revealed a novel, non-proteinogenic role of these molecules. Moreover, the finding that aged proteins from the human eye crystallin, teeth, bone, blood vessels or the brain incorporate D-aspartic acids to specific primary protein sequences fostered the hypothesis that aging might be related to D-amino acid isomerization of body proteins. The experimental confirmation that schizophrenia and neurodegenerative diseases modify plasma free D-amino acids or tissue levelsnurtured the opportunity of using D-amino acids as therapeutic agents for several disease treatments, a strategy that prompted the successful current application of D-amino acids to human medicine.

Advances in the extracellular signal-regulated kinase signaling pathway in silkworms, Bombyx mori (Lepidoptera)

Signaling pathways regulate the transmission of signals during organism growth and development, promoting the smooth and accurate completion of numerous physiological and biochemical reactions. The extracellular signal-regulated kinase (ERK) signaling pathway is an essential pathway involved in regulating various physiological processes, such as cell proliferation, differentiation, adhesion, migration, and more. This pathway also contributes to several important physiological processes in silkworms, including protein synthesis, reproduction, and immune defense against pathogens. Organizing related studies on the ERK signaling pathway in silkworms can provide a better understanding of its mechanism in Lepidopterans and develop a theoretical foundation for improving cocoon production and new strategies for pest biological control.

The Phosphoserine Phosphatase Alters the Free Amino Acid Compositions and Fecundity in Cyrtorhinus lividipennis Reuter

The mirid bug Cyrtorhinus lividipennis (Reuter) is an important predator that consumes eggs and young nymphs of the brown planthopper Nilaparvata lugens as a primary food source and thus becomes an important member of the rice ecosystem. We identified and characterized the ClPSP gene in C. lividipennis encoding the phosphoserine phosphatase enzyme. The ClPSP has an open reading frame (ORF) of 957 bp encoding a protein with a length of 294bp and it possesses a haloacid dehalogenase-like (HAD) hydrolase, phosphoserine phosphatase, eukaryotic-like (HAD_PSP_eu) conserved domain. Furthermore, the in silico analysis of the ClPSP gene unveiled its distinct characteristics and it serves as a key player in the modulation of amino acids. The ClPSP showed expression in all developmental stages, with higher expression observed in the ovary and fat body. Silencing the ClPSP by RNA interference (RNAi) significantly decreased PSP enzyme activity and expression compared to dsGFP at two days after emergence (2DAE). The dsPSP treatment altered free hemolymph amino acid compositions, resulting in a significant reduction of serine (Ser) and Arginine (Arg) proportions and a significant increase of Threonine (Thr), Cystine (Cys), and Tyrosine (Tyr) in the C. lividipennis female at 2 DAE. Additionally, a hindered total protein concentration in the ovary and fat body, and reduced vitellogenin (Vg) expression, body weight, and number of laid eggs, were also observed. The same treatment also prolonged the preoviposition period and hindered ovarian development. Our data, for the first time, demonstrated the influential role of the PSP gene in modulating the fecundity of C. lividipennis and provide a platform for future insect pest control programs using the PSP gene in modulating fecundity.

Identification and characterization of a serine racemase in the silkworm Bombyx mori

The pupae of lepidopterans contain high concentrations of endogenous d-serine. In the silkworm Bombyx mori, d-serine is negligible during the larval stage but increases markedly during the pupal stage, reaching 50% of the total free serine. However, the physiological function of d-serine and the enzyme responsible for its production are unknown. Herein, we identified a new type of pyridoxal 5'-phosphate (PLP)-dependent serine racemase (SR) that catalyzes the racemization of l-serine to d-serine in B. mori. This silkworm SR (BmSR) has an N-terminal PLP-binding domain that is homologous to mammalian SR and a C-terminal putative ligand-binding regulatory-like domain (ACT-like domain) that is absent in mammalian SR. Similar to mammalian SRs, BmSR catalyzes the racemization and dehydration of both serine isomers. However, BmSR is different from mammalian SRs as evidenced by its insensitivity to Mg2+/Ca2+ and Mg-ATP-which are required for activation of mammalian SRs-and high d-serine dehydration activity. At the pupal stage, the SR activity was predominantly detected in the fat body, which was consistent with the timing and localization of BmSR expression. The results are an important first step in elucidating the physiological significance of d-serine in lepidopterans.

Effect of NMDA receptor agonist and antagonist on spermatogonial stem cells proliferation in 2- and 3- dimensional culture systems

BACKGROUND

The main purpose of this study was to investigate the effect of D-serine (DS) and Dizocilpine (MK-801) on the proliferation of spermatogonial stem cells (SSCs) in two-dimensional (2D) and three-dimensional (3D) culture systems.

METHODS AND RESULTS

The SSCs of male NMRI mice were isolated by enzymatic digestion and cultured for two weeks. Then, the identity of SSCs was validated by anti-Plzf and anti-GFR-α1 antibodies via immunocytochemistry (ICC). The proliferation capacity of SSCs was evaluated by their culture on a layer of the decellularized testicular matrix (DTM) prepared from mouse testis, as well as two-dimensional (2D) with different mediums. After two weeks of the initiation of proliferation culture on 3D and 2D medium, the pre-meiotic at the mRNA and protein levels were evaluated via qRT-PCR and flow cytometry methods, respectively. The results showed that the proliferation rate of SSCs in 3D culture with 50 mM glutamic acid and 20 mM D-serine was significantly different from other groups after 14 days treatment. mRNA expression levels of promyelocytic leukemia zinc finger (Plzf) in 3D cultures supplemented by 20 mM D-serine and 50 mM glutamic acid were considerably higher than the 3D control group (p < 0.001). The flow cytometry analysis revealed that the amount of Plzf in the 2D-culture groups of SSCs with 20 mM MK-801 was considerably lower compared to the 2D-culture control group (p < 0.001).

CONCLUSIONS

This study indicated that decellularized testicular matrix supplemented with D-serine and glutamic acid could be considered a promising vehicle to support cells and provide an appropriate niche for the proliferation of SSCs.

Participation of D-serine in the development and reproduction of the silkworm Bombyx mori

The silkworm Bombyx mori contains high concentrations of free D-serine, an optical isomer of L-serine. To elucidate its function, we first investigated the localization of D-serine in various organs of silkworm larvae, pupae, and adult moths. Using immunohistochemical analysis with an anti-D-serine antibody, we found D-serine in the microvilli of midgut goblet and cylindrical cells and in peripheral matrix components of testicular and ovarian cells. By spectrophotometric analysis, D-serine was also found in the hemolymph and fat body. D-Alanine was not detected in the various organs by immunohistochemistry. Serine racemase, which catalyzes the inter-conversion of L- and D-serine, was found to co-localize with D-serine, and D-serine production from L-serine by intrinsic serine racemase was suggested. O-Phospho-L-serine is an inhibitor of serine racemase, and it was administered to the larvae to reduce the D-serine level. This reagent decreased the midgut caspase-3 level and caused a delay in spermatogenesis and oogenesis. The reagent also decreased mature sperm and egg numbers, suggesting D-serine participation in these processes. D-Serine administration induced an increase in pyruvate levels in testis, midgut, and fat body, indicating conversion of D-serine to pyruvate. On the basis of these results, together with our previous investigation of ATP biosynthesis in testis, we consider the possible involvement of D-serine in ATP synthesis for metamorphosis and reproduction.