A transcription factor glial cell missing (Gcm) in the freshwater crayfish Pacifastacus leniusculus

Evolution of glial cells: a non-bilaterian perspective

Nervous systems of bilaterian animals generally consist of two cell types: neurons and glial cells. Despite accumulating data about the many important functions glial cells serve in bilaterian nervous systems, the evolutionary origin of this abundant cell type remains unclear. Current hypotheses regarding glial evolution are mostly based on data from model bilaterians. Non-bilaterian animals have been largely overlooked in glial studies and have been subjected only to morphological analysis. Here, we provide a comprehensive overview of conservation of the bilateral gliogenic genetic repertoire of non-bilaterian phyla (Cnidaria, Placozoa, Ctenophora, and Porifera). We overview molecular and functional features of bilaterian glial cell types and discuss their possible evolutionary history. We then examine which glial features are present in non-bilaterians. Of these, cnidarians show the highest degree of gliogenic program conservation and may therefore be crucial to answer questions about glial evolution.

Analysis of cnidarian Gcm suggests a neuronal origin of glial EAAT1 function

In bilaterian central nervous systems, coordination of neurotransmission by glial cells enables highly sophisticated neural functions. The diversity of transcription factors (TFs) involved in gliogenesis suggests multiple evolutionary origins of various glial cell types of bilaterians. Many of these TFs including the glial cells missing (Gcm) are also present in genomes of Cnidaria, the closest outgroup to Bilateria, but their function remains to be elucidated. In this study, we analyzed the function of Gcm, a multifunctional TF involved in development of glial and non-glial cell types, in the sea anemone, Nematostella vectensis. siRNA-mediated knockdown of Nematostella Gcm altered expression of cell adhesion proteins, glutamate and GABA transporters, ion channels, metabolic enzymes, and zinc finger and Ets-related TFs. NvGcm and mRNAs of downstream genes are expressed in broad neural cell clusters. However, immunostaining of a NvGcm target protein, the glutamate transporter, NvEAAT1, visualized a novel class of cells with flat cell bodies and no clear processes. Together with the finding of unique morphological features of NvEAAT1-functioning cells, these data suggest that extracellular glutamate metabolism, one of major glial functions, is deployed downstream of Gcm in specific neural cell types in Cnidaria.

Blood cell formation in crustaceans

In crustacean animals the hemocytes are key players in immunity and of crucial importance for the health of the animals. Hemocytes are mainly produced in the hematopoietic tissue and from there released into the circulation where they finally mature. In this review we summarize the latest findings about crustacean hemocyte formation. The role of the extracellular matrix and crosslinking enzyme transglutaminase is discussed. Moreover, important growth factors, transcriptional regulation and recent findings about inducers of hematopoiesis are covered. Finally, we discuss the use of different markers for classification of crustacean hemocytes.

A haemocyte-expressed Methyltransf_FA domain containing protein (MFCP) exhibiting microbe binding activity in oyster Crassostrea gigas

The Methyltransf_FA domain is well-known as a key protein domain of enzyme synthesizing juvenile hormone, and Methyltransf_FA domain containing proteins (MFCPs) are widely existed in vertebrates and invertebrates. In the present study, a CgMFCP with a single Methyltransf_FA domain was screened from oyster Crassostrea gigas, and its open reading frame of CgMFCP was of 1128 bp, encoding a polypeptide of 376 amino acids with a signal peptide, a Methyltransf_FA domain and a transmembrane region. CgMFCP was clustered with FAMeTs from insecta and crustacea of arthropod. The mRNA transcripts of CgMFCP were detected in different tissues, with the extremely high expression level in haemocytes, which was 131.36-fold (p < 0.05) of that in gills. The expression level of CgMFCP protein was verified to be highly expressed in haemocytes. The expression level of CgMFCP mRNA in primarily cultured haemocytes significantly up-regulated at 3 h, 24 h and 48 h post LPS stimulation, which was 3.25-fold (p < 0.01), 2.04-fold (p < 0.05) and 3.59-fold (p < 0.01) compared to that in blank group. After the oysters were stimulated with Vibrio splendidus in vivo, the expression level of CgMFCP mRNA in haemocytes was also significantly up-regulated at 3 h, 12 h, and 24 h, which was 4.22-fold (p < 0.05), 4.39-fold (p < 0.05) and 6.35-fold (p < 0.01) of that in control group, respectively. By flow cytometry analysis, anti-rCgMFCP can label 95% of oyster haemocytes. And by fluorescence microscope analysis, CgMFCP was mainly distributed in cytomembrane of haemocytes. The recombinant CgMFCP (rCgMFCP) exhibited higher affinity towards MAN and LPS in a dose-dependent manner, while relatively lower affinity to PGN and poly (I:C). rCgMFCP also displayed binding activities towards Gram-negative bacteria (Vibrio anguillarum and V. splendidus), Gram-positive bacteria (Staphylococcu aureu) and fungi (Pichia pastoris). These results collectively indicated that CgMFCP specifically expressed in haemocytes and functioned as a pattern recognition receptor by binding to various microbes in oyster C. gigas, which provided insight into the function of Methyltransf_FA domain containing proteins.