Anesthesia for Echocardiography and Magnetic Resonance Imaging in the African Clawed Frog (Xenopus laevis)

This report describes an anesthesia technique that we used to study cardiovascular anatomy and physiology with echocardiography and cardiac magnetic resonance (CMR) in 46 African clawed frogs (Xenopus laevis) (n = 24 for electrocardiography and n = 22 for CMR). For administration of anesthesia, 3 holding tanks, one each for transportation, sedation, and recovery, were filled with filtered water, with 0.05% buffered tricaine methasulfonate solution (MS-222) added into the sedation tank. Fifteen minutes after the frog was placed in the sedation tank, a paper towel was soaked in MS-222 solution, and the frog was placed in a supine position and rolled 3 to 4 times in the soaked paper with the head and legs exposed. Vital signs were monitored and recorded throughout the procedure. After imagining, frogs were unrolled from the paper towel, placed in the recovery tank, and later returned to their home tank. Monitoring was discontinued when the frogs resumed typical activity. No mortality or complications were observed in frogs that underwent this procedure. Mean duration ±1 SD of anesthesia induction was 12 ± 5 min in the echocardiography group and 14 ± 6 min in the CMR group. The mean duration of anesthesia maintenance was 60 ± 18 min in the echocardiography group and 118 ± 37 min in the CMR group. An additional dose of anesthesia was necessary during maintenance for 9 of 24 (37%) frogs in the echocardiography group and 6 of 22 (27%) frogs in the CMR group. At the end of the procedure, the mean oxygen saturation was 66 ± 9% in the echocardiography group and 85 ± 6% in the CMR group, and heart rate was 48 ± 13 beats/min in the echocardiography group and 42 ± 7 beats/min in the CMR group. We conclude that the anesthesia technique of immersion in MS-222 is suitable for performing echocardiography and CMR imaging in this species without complications.

Comparison of oocyte mRNA localization patterns in sterlet Acipenser ruthenus and African clawed frog Xenopus laevis

In oocytes, RNA localization has critical implications, as assembly of proteins in particular subcellular domains is crucial to embryo development. The distribution of mRNA molecules can identify and characterize localized transcripts. The goal of this study was to clarify the origin of primordial germ cells in the oocyte body plan and to reveal the generation of cell lineages by localized RNAs. The distribution of 12 selected mRNAs in sterlet Acipenser ruthenus oocytes was investigated by qPCR tomography and compared with known patterns of mRNA localization in Xenopus laevis. We investigated the distribution of two gene clusters in the ooplasm along the animal-vegetal axis of the sturgeon oocyte, both of which showed clearly defined intracellular gradient pattern remarkably similar to their distribution in the frog oocyte. We elucidated the localization of sturgeon egg germplasm markers belonging to the vegetal group of mRNAs. The mRNAs coding otx1, wnt11, and veg1 found to be localized in the sturgeon animal hemisphere are, in contrast, distributed in the vegetal hemisphere in amphibian. Actinopterygii and Sarcopterygii, two major lineages of osteichthyan vertebrates, split about 476 Ma (Blair & Hedges, ), albeit basal lineages share conserved biological features. Acipenseriformes is one the most basal living lineages of Actinopterygii, having evolved about 200 Ma (Bemis, Birstein, & Waldman, ), contemporaneous with modern amphibians (Roelants et al., ).

Label-free real-time imaging of myelination in the Xenopus laevis tadpole by in vivo stimulated Raman scattering microscopy

The myelin sheath plays an important role as the axon in the functioning of the neural system, and myelin degradation is a hallmark pathology of multiple sclerosis and spinal cord injury. Electron microscopy, fluorescent microscopy, and magnetic resonance imaging are three major techniques used for myelin visualization. However, microscopic observation of myelin in living organisms remains a challenge. Using a newly developed stimulated Raman scattering microscopy approach, we report noninvasive, label-free, real-time in vivo imaging of myelination by a single-Schwann cell, maturation of a single node of Ranvier, and myelin degradation in the transparent body of the Xenopus laevis tadpole.

Oocyte triplet pairing for electrophysiological investigation of gap junctional coupling

Gap junctions formed by expressing connexin subunits in Xenopus oocytes provide a valuable tool for revealing the gating properties of intercellular gap junctions in electrically coupled cells. We describe a new method that consists of simultaneous triple recordings from 3 apposed oocytes expressing exogenous connexins. The advantages of this method are that in one single experiment, 1 oocyte serves as control while a pair of oocytes, which have been manipulated differently, may be tested for different gap junctional properties. Moreover, we can study simultaneously the gap junctional coupling of 3 different pairs of oocytes in the same preparation. If the experiment consists of testing the effect of a single drug, this approach will reduce the time required, as background coupling in control pairs of oocytes does not need to be measured separately as with the conventional 2 oocyte pairing. The triplet approach also increases confidence that any changes seen in junctional communication are due to the experimental treatment and not variation in the preparation of oocytes or execution of the experiment. In this study, we show the example of testing the gap junctional properties among 3 oocytes, 2 of which are expressing rat connexin36.

pEg7, a new Xenopus protein required for mitotic chromosome condensation in egg extracts

We have isolated a cDNA, Eg7, corresponding to a Xenopus maternal mRNA, which is polyadenylated in mature oocytes and deadenylated in early embryos. This maternal mRNA encodes a protein, pEg7, whose expression is strongly increased during oocyte maturation. The tissue and cell expression pattern of pEg7 indicates that this protein is only readily detected in cultured cells and germ cells. Immunolocalization in Xenopus cultured cells indicates that pEg7 concentrates onto chromosomes during mitosis. A similar localization of pEg7 is observed when sperm chromatin is allowed to form mitotic chromosomes in cytostatic factor-arrested egg extracts. Incubating these extracts with antibodies directed against two distinct parts of pEg7 provokes a strong inhibition of the condensation and resolution of mitotic chromosomes. Biochemical experiments show that pEg7 associates with Xenopus chromosome-associated polypeptides C and E, two components of the 13S condensin.