Locations, ultrastructural morphology, and putative functions of the branchial podocytes of the fresh water crab Potamon niloticus — Savigy (crustacea, decapoda, potamonidae)

Ion regulation in a freshwater crab, Potamonautes warreni: The effects of trace metal exposure

Crustaceans inhabiting metal-contaminated freshwaters are susceptible to toxic insult to their osmoregulatory systems. The main osmoregulatory organs of decapod crustaceans, the gills, are continually bathed in freshwater and are therefore at risk from trace metal impacts. The effects of chronic (21 d) exposure to raised dissolved concentrations of Zn, Cd, Cu and Pb on aspects of hydromineral balance were investigated in Potamonautes warreni, a freshwater crab endemic to rivers in South Africa at potential risk from trace metal contamination from mining operations. Generally, hydromineral balance of P. warreni was tolerant to chronic metal exposures although sublethal cadmium exposure of 860 µg.l^-1 for 21 days resulted in a reduced sodium concentration in the haemolymph. A chronic exposure to 43 µg.l^-1 cadmium produced an elevated maximum unidirectional sodium uptake, possibly resulting from acclimation to the metal exposure. Branchial Na⁺/K⁺-ATPase and V-Type H⁺-ATPase activity were not affected by chronic in vivo Cd (43 µg.l^-1) and Zn (500 µg.l^-1) exposures. An important aspect of ameliorating metal toxicity may be through antioxidants and therefore the effects of applying a reducing agent were tested following in vitro metal treatment. Inhibition of Na⁺/K⁺-ATPase could be prevented by pre-incubation with a reducing agent, indicating the importance of antioxidants in reducing metal toxicity in this species. Although this study demonstrates the physiological resilience of P. warreni to dissolved trace metal impacts, the energetic consequences of long-term exposure are as yet not known.

Comparative transcriptome analysis of the gills of Procambarus clarkii provides novel insights into the immune-related mechanism of copper stress tolerance

The red-swamp crayfish (Procambarus clarkii) is the most important economic shrimp species in China, and is an important model crustacean organism in many fields of research. In crustaceans, gills interface directly with the ambient environment and thus play a vital role in the toxicology. In the context of increasing environmental heavy metal pollution, the relationship between copper (Cu²⁺) stress and the immune response of P. clarkii has recently received considerable attention. However, impact of Cu²⁺ on the crayfish immune system is still not fully understood. In this study, we used Illumina sequencing technology to perform a transcriptome analysis of the gills of P. clarkii after 24 h of Cu²⁺ treatment. A total of 37,226,812 unigenes were assembled, and 1943 unigenes were significantly differentially expressed between the control and Cu²⁺ treatment groups. Functional categorization of differentially expressed genes (DEGs) revealed that genes related to antioxidant activity, detoxication, metabolic processes, biosynthetic processes, and immune system processes were differentially regulated during Cu²⁺ stress. In addition, DEGs in the immune system were classified as being related to the MAPK signaling pathway, purine metabolism, Toll and Imd signaling pathway, PI3K-Akt signaling pathway and Hippo signaling pathway. Five genes (CuZnSOD, CAT, IDH1, PHYH and DECR2) were significantly up-regulated in the peroxisome pathway, which plays an important role in reacting to oxidative stress. Importantly, qRT-PCR validation of the results for seven genes chosen at random (NDK, ATP6L, ATP5C1, RPS14, RPL22e, CTSF and HSP90A) confirmed the Illumina sequencing results. This study provides a valuable starting point for further studies to elucidate the molecular basis of the immune system's response to Cu²⁺ stress in crayfish.

An excretory organ in the Mystacocarida (Crustacea)

An excretory antennal gland, composed of only eight cells, is found entirely in the limb in the mystacocarid Derocheilocaris typica. The end sac is composed of podocytes, valve cells and cap cells. The podocytes contain enormous residual vesicles. There are few pedicel complexes, and they arise directly from the cell surface without intermediate foot processes. The excretory duct is entirely lined with microvilli, which are separated from the lumen by a modified layer of thin cuticle.

Thin and strong! The bioengineering dilemma in the structural and functional design of the blood-gas barrier

In gas exchangers, the tissue barrier, the partition that separates the respiratory media (water/air and hemolymph/blood), is exceptional for its remarkable thinness, striking strength, and vast surface area. These properties formed to meet conflicting roles: thinness was essential for efficient flux of oxygen by passive diffusion, and strength was crucial for maintaining structural integrity. What we have designated as "three-ply" or "laminated tripartite" architecture of the barrier appeared very early in the evolution of the vertebrate gas exchanger. The design is conspicuous in the water-blood barrier of the fish gills through the lungs of air-breathing vertebrates, where the plan first appeared in lungfishes (Dipnoi) some 400 million years ago. The similarity of the structural design of the barrier in respiratory organs of animals that remarkably differ phylogenetically, behaviorally, and ecologically shows that the construction has been highly conserved both vertically and horizontally, i.e., along and across the evolutionary continuum. It is conceivable that the blueprint may have been the only practical construction that could simultaneously grant satisfactory strength and promote gas exchange. In view of the very narrow allometric range of the thickness of the blood-gas barrier in the lungs of different-sized vertebrate groups, the measurement has seemingly been optimized. There is convincing, though indirect, evidence that the extracellular matrix and particularly the type IV collagen in the lamina densa of the basement membrane is the main stress-bearing component of the blood-gas barrier. Under extreme conditions of operation and in some disease states, the barrier fails with serious consequences. The lamina densa which in many parts of the blood-gas barrier is <50 nm thin is a lifeline in the true sense of the word.