Frog Development

Embryology - 2 Dec 2023        Expand to Translate
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Introduction

Adult Frogs

Hans Spemann discoverer of the organiser region (primitive node) for gastrulation.

The frog has been historically been used as an amphibian animal model of development due to the ease of observation from the fertilized egg through to tadpole stage. The later metamorphosis of the tadpole to frog has also been studied for hormonal controls and limb development. There have also been many different species used in these developmental studies.

The frog was historically used by many of the early embryology investigators and currently there are many different molecular mechanisms concerning development of the frog. The 2012 Nobel prize in medicine was recently awarded to John Gurdon for his 1960's experiments involving nuclear transplantation with adult nuclei into frog eggs, these studies were the precursor to current research in stem cells.

The African clawed frog (Xenopus laevis) has been used in many embryological and electrophysiological studies as well as the basis of a historic pregnancy test. The advantages of this frog is the fertility cycle can be easliy controlled and the eggs develop entirely independently and easily visible to the investigator. You can see an overview of the frog life cycle with links to specific stages as well as movies of the early process of gastrulation. This animal model has also shown that localization of maternal messenger RNA (eg vegetal and review) appears to play a key role in the development of early embryological patterns.

The Leopard frog (Rana pipiens) in 1952 became the first successful nuclear transfer experiment. Nuclear transfer is an embryological technique, and involves removal of the nucleus from an egg and replacement with the nucleus of another donor cell. This experiment paved the way for what we know today as the field of cloning.

In Australia, the cane toad (Bufo marinus) species was introduced in 1935 to control cane insect pests. It has now itself become an introduced pest and has also been studied/used more in order to try and biologically control. The area which they occupy has continued to expand. This toad has a poisonous secretion that is extremely toxic and should be handled with care at all times.

Some Recent Findings

Xenopus red fluorescence

Pinhead antagonizes Admp to promote notochord formation "Dorsoventral patterning of a vertebrate embryo critically depends on the activity of Smad1 that mediates signaling by BMP proteins, anti-dorsalizing morphogenetic protein (Admp), and their antagonists. Pinhead (Pnhd), a cystine-knot-containing secreted protein, is expressed in the ventrolateral mesoderm during Xenopus gastrulation; however, its molecular targets and signaling mechanisms have not been fully elucidated. Our mass spectrometry-based screen of the gastrula secretome identified Admp as Pnhd-associated protein. We show that Pnhd binds Admp and inhibits its ventralizing activity by reducing Smad1 phosphorylation and its transcriptional targets. Importantly, Pnhd depletion further increased phospho-Smad1 levels in the presence of Admp. Furthermore, Pnhd synergized with Chordin and a truncated BMP4 receptor in the induction of notochord markers in ectoderm cells, and Pnhd-depleted embryos displayed notochord defects. Our findings suggest that Pnhd binds and inactivates Admp to promote notochord development. We propose that the interaction between Admp and Pnhd refines Smad1 activity gradients during vertebrate gastrulation."

More recent papers

This table allows an automated computer search of the external PubMed database using the listed "Search term" text link. This search now requires a manual link as the original PubMed extension has been disabled. The displayed list of references do not reflect any editorial selection of material based on content or relevance. References also appear on this list based upon the date of the actual page viewing. References listed on the rest of the content page and the associated discussion page (listed under the publication year sub-headings) do include some editorial selection based upon both relevance and availability. More? References | Discussion Page | Journal Searches | 2019 References | 2020 References Search term: Frog Embryology <pubmed limit=5>Frog Embryology</pubmed>

Older papers

Anosmin-1 is essential for neural crest and cranial placodes formation in Xenopus "During embryogenesis vertebrates develop a complex craniofacial skeleton associated with sensory organs. These structures are primarily derived from two embryonic cell populations the neural crest and cranial placodes, respectively. ...Anos1 was identified as a target of Pax3 and Zic1, two transcription factors necessary and sufficient to generate neural crest and cranial placodes. Anos1 is expressed in cranial neural crest progenitors at early neurula stage and in cranial placode derivatives later in development. We show that Anos1 function is required for neural crest and sensory organs development in Xenopus, consistent with the defects observed in Kallmann syndrome patients carrying a mutation in ANOS1." EphA7 regulates claudin6 and pronephros development in Xenopus "Here we studied the roles of the Eph receptor EphA7 and its soluble form in Xenopus pronephros development. EphA7 is specifically expressed in pronephric tubules at tadpole stages and knockdown of EphA7 by a translation blocking morpholino led to defects in tubule cell differentiation and morphogenesis. A soluble form of EphA7 (sEphA7) was also identified. ...Our work suggests a role of EphA7 in the regulation of cell adhesion during pronephros development, whereas sEphA7 works as an antagonist." N1-Src kinase is required for primary neurogenesis in Xenopus tropicalis "The presence of the neuronal-specific N1-Src splice variant of the C-Src tyrosine kinase is conserved through vertebrate evolution, suggesting an important role in complex nervous systems. The Src family of non-receptor tyrosine kinases act in signalling pathways that regulate cell migration, cell adhesion and proliferation. Srcs are also enriched in the brain where they play key roles in neuronal development and neurotransmission. Vertebrates have evolved a neuron-specific splice variant of C-Src, N1-Src, which differs from C-Src by just five or six amino acids. N1-Src is poorly understood and its high similarity to C-Src has made it difficult to delineate its function. Using antisense knockdown of the n1-src microexon, we have studied neuronal development in the Xenopus embryo in the absence of n1-src, whilst preserving c-src Loss of n1-src causes a striking absence of primary neurogenesis, implicating n1-src in the specification of neurons early in neural development." Neural System Development Endocrine disruption by environmental gestagens in amphibians - A short review supported by new in vitro data using gonads of Xenopus laevis "Endocrine disruption caused by various anthropogenic compounds is of persisting concern, especially for aquatic wildlife, because surface waters are the main sink of these so-called endocrine disruptors (ED). In the past, research focused on (anti)estrogenic, (anti)androgenic, and (anti)thyroidal substances, affecting primarily reproduction and development in vertebrates; however, other endocrine systems might be also targeted by ED. Environmental gestagens, including natural progestogens (e.g. progesterone (P4)) and synthetic progestins used for contraception, are supposed to affect vertebrate reproduction via progesterone receptors. In the present paper, we review the current knowledge about gestagenic effects in amphibians, focussing on reproduction and the thyroid system. In addition, we support the literature data with results of recent in vitro experiments, demonstrating direct impacts of the gestagens levonorgestrel (LNG) and P4 on sexually differentiated gonads of larval Xenopus laevis. The results showed a higher susceptibility of female over male gonads to gestagenic ED. Only in female gonads LNG, but not P4, had direct inhibitory effects on gene expression of steroidogenic acute regulatory protein and P450 side chain cleavage enzyme, whereas aromatase expression decreased in reaction to both gestagens. Surprisingly, beyond the expected ED effects of gestagens on reproductive physiology in amphibians, LNG drastically disrupted the thyroid system, which resembles direct effects on thyroid glands and pituitary along the pituitary-thyroid axis disturbing metamorphic development. In amphibians, environmental gestagens not only affect the reproductive system but at least LNG can impact also development by disruption of the thyroid system." Gonad Development | Thyroid Development Review - Xenopus Limb bud morphogenesis "Xenopus laevis, the South African clawed frog, is a well-established model organism for the study of developmental biology and regeneration due to its many advantages for both classical and molecular studies of patterning and morphogenesis. While contemporary studies of limb development tend to focus on models developed from the study of chicken and mouse embryos, there are also many classical studies of limb development in frogs. These include both fate and specification maps, that, due to their age, are perhaps not as widely known or cited as they should be. This has led to some inevitable misinterpretations- for example, it is often said that Xenopus limb buds have no apical ectodermal ridge, a morphological signalling centre located at the distal dorsal/ventral epithelial boundary and known to regulate limb bud outgrowth. These studies are valuable both from an evolutionary perspective, because amphibians diverged early from the amniote lineage, and from a developmental perspective, as amphibian limbs are capable of regeneration. Here, we describe Xenopus limb morphogenesis with reference to both classical and molecular studies, to create a clearer picture of what we know, and what is still mysterious, about this process." Limb Development Variation in the schedules of somite and neural development in frogs "The timing of notochord, somite, and neural development was analyzed in the embryos of six different frog species, which have been divided into two groups, according to their developmental speed. Rapid developing species investigated were Xenopus laevis (Pipidae), Engystomops coloradorum, and Engystomops randi (Leiuperidae). The slow developers were Epipedobates machalilla and Epipedobates tricolor (Dendrobatidae) and Gastrotheca riobambae (Hemiphractidae). ...We propose that these changes are achieved through differential timing of developmental modules that begin with the elongation of the notochord during gastrulation in the rapidly developing species. The differences might be related to the necessity of developing a free-living tadpole quickly in rapid developers." Unfertilized frog eggs die by apoptosis following meiotic exit "Here, we report that the vast majority of naturally laid unfertilized eggs of the African clawed frog Xenopus laevis spontaneously exit metaphase arrest under various environmental conditions and degrade by a well-defined apoptotic process within 48 hours after ovulation. The main features of this process include cytochrome c release, caspase activation, ATP depletion, increase of ADP/ATP ratio, apoptotic nuclear morphology, progressive intracellular acidification, and egg swelling. Meiotic exit seems to be a prerequisite for execution of the apoptotic program." Dorsal-Ventral patterning: crescent is a dorsally secreted Frizzled-related protein that competitively inhibits Tolloid proteases "In Xenopus, dorsal-ventral (D-V) patterning can self-regulate after embryo bisection. This is mediated by an extracellular network of proteins secreted by the dorsal and ventral centers of the gastrula. .... In sum, Crescent is a new component of the D-V pathway, which functions as the dorsal counterpart of Sizzled, through the regulation of chordinases of the Tolloid family." Aging of Xenopus tropicalis eggs leads to deadenylation of a specific set of maternal mRNAs and loss of developmental potential Repression of zygotic gene expression in the Xenopus germline. "Primordial germ cells (PGCs) in Xenopus are specified through the inheritance of germ plasm. During gastrulation, PGCs remain totipotent while surrounding cells in the vegetal mass become committed to endoderm through the action of the vegetal localized maternal transcription factor VegT. We find that although PGCs contain maternal VegT RNA, they do not express its downstream targets at the mid-blastula transition (MBT)."

Taxon

Xenopus Laevis

Eukaryotae; mitochondrial eukaryotes; Metazoa; Chordata;Vertebrata; Amphibia; Batrachia; Anura; Mesobatrachia; Pipoidea;Pipidae; Xenopodinae; Xenopus

Rana pipiens

Rana pipiens

Taxonomy Id: 8404 Preferred common name: northern leopard frog Rank: species

Genetic code: Translation table 1 (Standard) Mitochondrial genetic code: Translation table 2 Lineage( abbreviated ):

Eukaryota; Metazoa; Chordata; Craniata; Vertebrata; Amphibia; Batrachia; Anura; Neobatrachia; Ranoidea; Ranidae; Raninae; Rana

Frog Life Cycle

Development Timeline

Gastrulation

Typical frog development at 18oC from fertilised egg. 0 hours - fertilization of the egg 1 hours - formation of the gray crescent due to pigment migration 3.5 hours - early cleavage 4.5 hours - blastula stage(coeloblastula with eccentric blastocoel 26 hours - gastrulation 26 hours - early crescent shaped dorsal lip 34 hours middle semicircular blastoporal lip 42 hours late circular blastoporal lip 50 hours - neurulation 50 hours - early medullary plate 62 hours - middle neural folds converging 67 hours - late neural tube formed and ciliation of embryo 84 hours - tail bud stage(early organogeny) 96 hours - muscular response to tactile stimulation 118 hours - early heart beat, development of gill buds 140 hours - hatching and gill circulation 162 hours - mouth opens and cornea becomes transparent 192 hours - tail fin circulation established 216 hours - degeneration of external gills, formation of operculum, development of embryonic teeth 240 hours - opercular fold over brachial chamber except for spiracle and internal gills 255 hours - prolonged larval stage with refinement of organs 270 hours - development of hindlimbs, internal development of forelimbs in opercular cavity 275 hours - projection of forelimbs through operculum, left side first 280 hours - absorption of the tail and reduction in size of the gut 284 hours - metamorphosis complete, emergence from water as miniature, air breathing frog

‎‎Frog Early Division Page | Play

Stages in the Normal Development of Rana pipiens

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  Early Stages

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  Middle Stages

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  Late Stages

Links: Embryology of the Leopard Frog Rana pipiens

Oocyte Balbiani body

Frog Eggs

• spherical cytoplasmic region that forms within the oocyte in early oogenesis and then fragments and disperses in late oogenesis.
• membrane-less structure consisting of mitochondria, endoplasmic reticulum (ER), membranous vesicles and lipid droplets.

Xenopus stage I oocytes

• Balbiani body is ∼40 μm in diameter
• contains half a million mitochondria, with different morphology and metabolism from other cytoplasmic mitochondria
• rich in membranous vesicles, and ER cysternae.
• vegetal apex (METRO region) contains germinal granules and localized RNAs
• Xlsirts
  • family of interspersed repeat RNAs that contain from 3 to 13 repeat units (each 79 to 81 nucleotides long) flanked by unique sequences.
  • homologous to the mammalian Xist gene involved in X chromosome inactivation
  • stage 2 oocytes - appears first in the mitochondrial cloud (Balbiani body)
  • stage 3 oocytes - translocated as island-like structures to the vegetal cortex coincident with the localization of the germ plasm.

Germ Layers

The following paper cartoons show models of signaling mechanisms that occur during early development of the germ cell layers (ectoderm, mesoderm and endoderm).

Neural

Comparative brain anatomy frog and dog models.

Cornea

Frog Cornea Timeline

Stage	Event
stage 25	cornea starts from a simple embryonic epidermis overlying developing optic vesicle
stage 30	detachment of lens placode, cranial neural crest cells start to invade the space between the lens and the embryonic epidermis to construct the corneal endothelium.
stage 41	second wave of migratory cells containing presumptive keratocytes invades the matrix, leading to formation of inner cornea and outer cornea. A unique cell mass (stroma attracting center) connects the two layers like the center pole of a tent.
stage 48	secondary stromal keratocytes individually migrate to the center and form the stroma layer.
stage 60	stroma space is filled by collagen lamellae and keratocytes, and the stroma attracting center disappears. At early metamorphosis, embryonic epithelium gradually changes to adult corneal epithelium, covered by microvilli.
stage 62	embryonic epithelium thickens and cell death is observed in the epithelium, coinciding with eyelid opening.
After metamorphosis	cornea has attained the adult structure of three cellular layers, epithelium, stroma, and endothelium, and between the cellular layers lie two acellular layers (Bowman's layer and Descemet's membrane)
Table data from Xenopus laevis | frog | vision

Links: Cornea Development | Vision Development

Metamorphosis

Metamorphosis of the frog, Rana catesbiana.

Sequence from left to right, top and bottom:

1. tadpole
2. tadpole with hind legs only
3. tadpole with two pairs of legs
4. tadpole with disappearing tail, ready to emerge from water to land
5. immature terrestrial frog
6. mature frog

Xenbase

Xenbase is a Xenopus model organism computer database with 4 GB of data in many hundreds of tables that has recently (2012) been updated, as described in the abstract of an NAR article.

"Xenbase (http://www.xenbase.org) is a model organism database that provides genomic, molecular, cellular and developmental biology content to biomedical researchers working with the frog, Xenopus and Xenopus data to workers using other model organisms. As an amphibian Xenopus serves as a useful evolutionary bridge between invertebrates and more complex vertebrates such as birds and mammals. Xenbase content is collated from a variety of external sources using automated and semi-automated pipelines then processed via a combination of automated and manual annotation. A link-matching system allows for the wide variety of synonyms used to describe biological data on unique features, such as a gene or an anatomical entity, to be used by the database in an equivalent manner. Recent updates to the database include the Xenopus laevis genome, a new Xenopus tropicalis genome build, epigenomic data, collections of RNA and protein sequences associated with genes, more powerful gene expression searches, a community and curated wiki, an extensive set of manually annotated gene expression patterns and a new database module that contains data on over 700 antibodies that are useful for exploring Xenopus cell and developmental biology."

Historic Researchers

Wilhelm Roux (1850 – 1924)	Hans Spemann (1869 - 1941)	John Gurdon (1933 - )
A German zoologist and pioneer of experimental embryology. Experimented by pricking and destroying one of the two blastomeres, to obtain half an embryo from the other.	A German embryologist who worked extensively on amphibian development and was the discoverer of the organiser region (or primitive node) the controller of gastrulation. Received the 1935 Nobel Prize in Physiology or Medicine "for his discovery of the organizer effect in embryonic development".	An English embryologist in 1962 used nuclear transplantation and cloning to show that the nucleus of a differentiated somatic cell retains the totipotency necessary to form a whole organism. Received the 2012 Nobel Prize "for the discovery that mature cells can be reprogrammed to become pluripotent".

References

Books

Rugh, R. The Frog Its Reproduction and Development The Blakiston Company, New York, 1951.

Reviews

Kaneda T & Motoki JY. (2012). Gastrulation and pre-gastrulation morphogenesis, inductions, and gene expression: similarities and dissimilarities between urodelean and anuran embryos. Dev. Biol. , 369, 1-18. PMID: 22634398 DOI.

Jones CM & Smith JC. (2008). An overview of Xenopus development. Methods Mol. Biol. , 461, 385-94. PMID: 19030813 DOI.

del Pino EM, Venegas-Ferrín M, Romero-Carvajal A, Montenegro-Larrea P, Sáenz-Ponce N, Moya IM, Alarcón I, Sudou N, Yamamoto S & Taira M. (2007). A comparative analysis of frog early development. Proc. Natl. Acad. Sci. U.S.A. , 104, 11882-8. PMID: 17606898 DOI.

Articles

TAYLOR AC & KOLLROS JJ. (1946). Stages in the normal development of Rana pipiens larvae. Anat. Rec. , 94, 7-13. PMID: 21013391

Search Pubmed

Search Pubmed: frog development | xenopus development

Bufo marinus

Additional Images

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  Sonic hedgehog expression

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  Sonic hedgehog expression

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  Adult female xenopus laevis with eggs

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  Germ layer signaling

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  Germ layer signaling

Historic Images

Bailey, F.R. and Miller, A.M. (1921). Text-Book of Embryology. Early development of the frog Fig. 26. Section through the fully formed ovarian egg of a frog. Fig. 27. A frog's egg before and after fertilization, showing the formation of the gray crescent. Fig. 28. Cleavage of the frog's egg. Fig. 29. From a sagittal section through blastula of frog. Fig. 30. Diagrams showing the position of the blastopore at successive stages of gastrulation in the frog's egg. Fig. 31. Median sagittal sections showing successive stages of gastrulation in the frog's egg Fig. 32. Transverse section of embryo of frog (Rana fusca). Fig. 33. Transverse section through embryo of frog (Rana fusca). Fig. 34. Portion of a transverse section still continuous at the lower lateral angles of the larva of a frog (Rana fusca) Fig. 35. Diagrams of median sagittal sections through an eight-cell stage and four stages during gastrulation of the frog's egg. Fig. 36. Postero-lateral views of successive stages following gastrulation in the frog. Fig. 37. Median sagittal sections of frog larvae. Fig. 349. Section of a sympathetic ganglion in the coeliac region of a frog (Rana esculenta). Fig. 373. Transverse section through dorsal part of embryo of frog (Rana fusca).

External Links

External Links Notice - The dynamic nature of the internet may mean that some of these listed links may no longer function. If the link no longer works search the web with the link text or name. Links to any external commercial sites are provided for information purposes only and should never be considered an endorsement. UNSW Embryology is provided as an educational resource with no clinical information or commercial affiliation.

• Xenbase A database of information pertaining to the cell and developmental biology of the frog, Xenopus
• Xenopus Laboratory List A database of Labs studying Xenopus
• Xenopus Microarrays
• Digital photographs of Xenopus stages (2005)
• Xenopus Cell Biology
• The Xenopus Molecular Marker Resource An electronic library of information on embryonic development of the frog, Xenopus laevis | Index page for all Markers | whole mount staining patterns
  • Molecular Markers of Development: cement gland XA, XAG, XCG | early mesoderm - BMP2, BMP4, Chordin, goosecoid, Mix,[Marker_pages/organizer/noggin.html noggin], Xbra, Xnr3, Xwnt-8, XVent1 and XVent2 | endothelial - Xl-fli | germ cells - Xpat | heart - cardiac troponin I , XNKX-2.5, XTin1 (XNKX-2.3) | lateral line - tor70, [Marker_pages/CNS/2G9.html 2G9] | muscle - 5A3, 12/101, cardiac actin, XMyf-5, XMyoD | neural crest - Slug, XTwist , xAP2 | notochord - Xnot, tor70 | pronephros - [Marker_pages/pronephros/3G8.html 3G8 ], Wilms' tumor (xWT1), Xlim-1, Xwnt-4 | pronephric duct - 4A6
• Frogs of Greater Brisbane Region (Australia)

• Developmental Biology- Laurie Iten's Serially Sectioned Frog and Chick Embryos
• Developmental Biology- Jeff Hardin's Amphibian Embryology Tutorial
• NIH- Organisms for biomedical research
• Columbia University Kelley Lab - The natural and unnatural histories of xenopus laevis

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Cite this page: Hill, M.A. (2023, December 2) Embryology Frog Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Frog_Development

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© Dr Mark Hill 2023, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G