Xenopus Laevis and Developmental Biology

Abstract

Summary 1. Because of the present popularity of Xenopus laevis for research in developmental biology, a review of the literature on this animal has been undertaken which emphasizes the anatomical, physiological and developmental features in which it differs from other anuran Amphibia. The need for caution in generalizing from observations on Xenopus to other vertebrates is stressed. 2. Earlier literature and the use of Xenopus for pregnancy testing have been surveyed briefly. Some of the peculiarities of this genus are: the prevalence of pulmonary rather than cutaneous or branchial respiration in the larva, with concomitant modifications of the vascular system; the larval filter‐feeding mechanism; the unusual development of the forelimbs, outside the gill chamber; and a number of features of musculature and skeleton in the adult which may be regarded either as primitive or as neotenous, or as specializations for aquatic life. Urodele‐like features of the morphology of the pituitary and pineal glands are also mentioned. 3. Recent work on the germ cells and their origin in Xenopus is reviewed in Section III. The germ plasm has been traced from early cleavage stages into germ cells whose identity and genetic characteristics may be traced by reciprocal transplants between anucleolate and normal Xenopus. This plasm is thought to contain redundant copies of DNA from the maternal oocyte, which may thus get passed on to the next generation. During oogenesis, yolk proteins originate from maternal liver protein, and both yolk platelets and pigment granules appear to form in association with mitochondria. The yolk platelets evidently contain both DNA and RNA, and the mitochondria also contain both DNA, of a circular form, and ribosomal RNA. In the oocyte nucleus, special interest has been focused recently on the extrachromo‐somal DNA which arises from the nucleolar organizer regions of chromosomes. This DNA later forms the cores of the nucleoli. A number of synthetic processes can take place in the oocyte cytoplasm in the absence of the nucleus, and in the presence of foreign messenger‐RNA. Ribosomal RNA synthesis shows at first an excess of 5 s over 18 s and 28 s forms. 4. Spermatogenesis has been studied little in Xenopus. Two unusual features are the absence of seminal vesicles for sperm storage and the spiral shape of the sperm head. By techniques involving destruction of the female pronucleus with ultraviolet light, or suppression of polar‐body formation, androgenetic haploids, as well as triploids and tetraploids, have been produced in this species. Paternal genes begin to act at the onset of gastrulation, when nucleoli appear and major rRNA synthesis begins. This situation is sometimes presumed to typify events in all Amphibia ‐perhaps all vertebrates ‐ but the assumption is unjustified, since in mammals there is much variation in the time of onset of rRNA synthesis, from the evidence so far available. 5. During cleavage in Xenopus, which appears to follow the same pattern as in other Amphibia, septate junctions may ...

Studies on the biology and taxonomy of Diplostomulum (Tylodelphylus) xenopodis from the African clawed toad, Xenopus laevis

“…All specimens were adult, the nose to vent length of males was 58-85 mm (mean 73 mm) and that of females was 63-120mm (mean 90 mm). The age of the toads is difficult to estimate; Deuchar (1972) reported that males stop growing at maturity (two years) but females grow continuously. Comparison of the present specimens with laboratory-raised toads indicates a minimum age for all individuals of about three years and the size of some females suggests an age of at least ten years.…”

Prevalence of Batrachochytrium dendrobatidis in Xenopus Collected in Africa (1871–2000) and in California (2001–2010)

“…This practice persisted through the 1970’s. Though no longer used for pregnancy testing, Xenopus have since become a major animal model in biomedical and basic science research [8]. Significant populations of Xenopus (largely X. laevis and to a lesser extent, X. tropicalis ) are currently housed in research laboratories.…”

The photoreceptors and pigment epithelium of the larvalXenopusretina: morphogenesis and outer segment renewal

“…In view of the considerable interest in the development of the visual system (see Gaze 1970;Jacobson 1970;Hollyfield 1971;Straznicky & Gaze 1971;Deuchar 1972;Horder & Spitzer 1973;Deuchar 1975;Jacobson 1976a; and reviews by Jacobson 19766 and Keating & Kennard 1976), knowledge about the differentiation of its photoreceptors and pigment epithelium (p.e.) is surprisingly limited (Saxen 1954;Lanzavecchia i960;Dixon & Cronly-Dillon 1972;Grillo & Rosenbluth 1972;Chung, Stirling & Gaze 1975;Witkovsky et al 1976).…”