Techniques for Rapidly Sampling Six Crucial Organs in Adult Xenopus

Summary

This article presents a guide for sampling six significant and diverse organs in adult Xenopus that can be rapidly and easily accessed: the heart ventricle, liver lobe, pancreas, fat bodies, paired kidneys, and skin.

Abstract

Xenopus has been a powerful model organism for understanding vertebrate development and disease for over a hundred years. While experimental analysis and dissection techniques of the embryo have been well documented, descriptions of adult Xenopus structures and organs, together with techniques for working with adults, have not been updated to take into consideration the requirements of such modern approaches as quantitative proteomics and single-cell transcriptomics. The cell-type and gene-centric perspectives require contrasting observations in embryonic stages to those in adult tissues. The organs of the larva undergo significant changes in their overall structure, morphology, and anatomical location all along the larval to adult transition, most notably during massive metamorphosis remodeling. Establishing robust standards for organ identification and dissection is crucial to ensure datasets resulting from studies performed at different laboratories can be consistent. The present protocol identifies six of the organs in the adult Xenopus, demonstrating methods for dissection and sampling of the heart ventricle, liver, fat body, pancreas, paired kidney, and skin of the adult Xenopus. Depending on the preservation methods, the dissected organs can be used for quantitative proteomics, single cell/nuclei transcriptomics, in situ hybridization, immunohistochemistry, histology, etc. This protocol aims to standardize tissue sampling and facilitate multi-lab investigations of the adult organ systems.

Introduction

Though the "digital dissection" of adult Xenopus” is available¹, replicable organ and tissue sampling of adult Xenopus remains challenging without the detailed instruction available for other adult models (e.g. mice^2,3,4). This article aims to provide clear guidance for accurate and replicable organ sampling of adult Xenopus similar to what is currently available for their larvae⁵. An emphasis is placed on ease of completion to maintain maximum freshness and make the protocol accessible to all users.

Though there is a thorough dissection guide for Rana sp.⁶, as well as numerous classroom dissection guides for other anurans⁷, no Xenopus dissection and sampling guide is currently available. For those not familiar with sampling practices or amphibian anatomy, the small differences between Xenopus and other anurans render these resources suboptimal for replicable tissue sampling.

Many valuable tissues are not included and are even discarded in the present guide; this is to ensure tissue freshness. Six samples are limited enough to ensure that these tissues can be collected in under an hour after the heart starts beating, regardless of the experience or skill level of the user. More advanced and detailed guides for collecting many other tissues are under preparation as separate companion papers.

For less experienced users, it is always recommended that this protocol be first attempted on animals being euthanized for reasons other than experimentation before sampling any animals that are challenging to replace (i.e., transgenics, animals of advanced age, etc). Ideally, all animals sampled will be healthy and, if female, will not have been ovulated in the past two weeks.

Protocol

All experiments were performed in accordance with the rules and regulations of the Harvard Medical School IACUC (Institutional Animal Care and Use Committee) (IS 00001365_3). The representative results are shown for both a perfused and unperfused mature albino male Xenopus laevis. 1. Experimental preparation NOTE: If perfusion protocol8 is being followed before sampling, skip to step 2.2. Ensure that the…

Representative Results

By utilizing Figure 1 to Figure 20 and following all steps of this protocol, the heart ventricle, the left lobe of the liver, the pancreas, the left fat bodies, paired kidneys, and a flap of skin were cleanly excised within an hour of euthanasia. Within this time, the samples are rinsed and trimmed so that they will appear, as shown in Figure 21. <img alt="Figur…

Discussion

As this protocol aims to maximize freshness, some samples may include undesired tissues. For example, the hepatopancreatic duct and some mesentery are sampled with the pancreas, and some peritoneal tissue, adrenal glands, and ureters will always be sampled with the paired kidneys.  If freshness is not a concern, then more precise sampling can be achieved using modified techniques.

The appearance and location of organs are comparable between sexes and species of Xenopus. However, …

Materials

5x Magnifying Glass with LED Light and Stand	amazon.com	B08QJ6J8P1	light must not produce heat
Disposable Transfer Pipets	VWR	414004-036
Dissecting Fine-Pointed Forceps	Fisher Scinetific	08-875
Dissecting scissors sharp piont, straight 6.5"	VWR	76457-374
Dissection Tray	Fisher Scinetific	14-370-284	styrofoam sheets are an acceptable alternative
Euthanasia container	US Plastic	Item 2860	alternative opaque containers acceptable
Euthanasia container lid	US Plastic	Item 3047
Iridectomy Scissors 6"	vwr	470018-938	iris scissors are an acceptable alternative
MS-222: Syncaine (formerly tricaine)	Pentair AES	TRS1
PBS 1x	Corning	21-040-CV
Sodium Bicarbonate, Powder, USP	Fisher Scientific	18-606-333
Specimen Forceps, Serrated	VWR	82027-442
T-Pins for Dissecting	Fisher Scinetific	S99385