Frog Development

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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.[1]

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.

Frog Links: Frog Development | 2009 Student Project | Hans Spemann | Wilhelm Roux | 1921 Early Frog Development | 1951 Rana pipiens Development | Rana pipiens Images | Frog Glossary | John Gurdon | Category:Frog | Animal Development

Some Recent Findings

Xenopus red fluorescence[2]
  • Variation in the schedules of somite and neural development in frogs[3] "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[4]"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 PMID21295563 "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[5]
  • Repression of zygotic gene expression in the Xenopus germline. [6] "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)."
More recent papers
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This table shows an automated computer PubMed search using the listed sub-heading term.

  • Therefore the list of references do not reflect any editorial selection of material based on content or relevance.
  • References appear in 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.

Links: References | Discussion Page | Pubmed Most Recent | Journal Searches

Search term: Frog Embryology

Matthias Tisler, Axel Schweickert, Martin Blum Xenopus, an ideal model organism to study laterality in conjoined twins. Genesis: 2017, 55(1-2); PubMed 28132423

Hidehiko Inomata Scaling of pattern formations and morphogen gradients. Dev. Growth Differ.: 2017; PubMed 28097650

M Smutná, J Priebojová, J Večerková, K Hilscherová Retinoid-like compounds produced by phytoplankton affect embryonic development of Xenopus laevis. Ecotoxicol. Environ. Saf.: 2016, 138;32-38 PubMed 27992848

Lorenzo Alibardi Microscopic observations show invasion of inflammatory cells in the limb blastema and epidermis in pre-metamorphic frog tadpoles which destroy the Apical Epidermal Cup and impede regeneration. Ann. Anat.: 2016; PubMed 27986640

Chao Wu, Yuhui Zhang, Lihong Chai, Hongyuan Wang Oxidative stress, endocrine disruption, and malformation of Bufo gargarizans embryo exposed to sub-lethal cadmium concentrations. Environ. Toxicol. Pharmacol.: 2016, 49;97-104 PubMed 27984779


Xenopus Laevis

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

Xenopus development.jpg

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

Frog lifecycle.jpg

Development Timeline


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
Xenopus early division 01 icon.jpg
 ‎‎Frog Early Division
Page | Play

Stages in the Normal Development of Rana pipiens

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[7]
    • 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[8] show models of signaling mechanisms that occur during early development of the germ cell layers (ectoderm, mesoderm and endoderm).

Frog germ layer signaling.jpg Frog germ layer signaling 01.jpg


Comparative brain anatomy frog-dog.jpg

Comparative brain anatomy frog and dog models.


This developmental timeline is from a recent Xenopus laevis cornea study[9]

  • stage 25 - cornea starts from a simple embryonic epidermis overlying the developing optic vesicle.
  • stage 30 - detachment of the 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 - a second wave of migratory cells containing presumptive keratocytes invades the matrix leading to the 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 - many secondary stromal keratocytes individually migrate to the center and form the stroma layer.
  • stage 60 - the stroma space is filled by collagen lamellae and keratocytes, and the stroma attracting center disappears. At early metamorphosis, the embryonic epithelium gradually changes to the adult corneal epithelium, which is covered by microvilli.
  • stage 62 - the 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)

Links: Cornea Development | Vision Development


Metamorphosis of the frog, Rana catesbiana.

Rugh 010.jpg

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 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.[10]

"Xenbase ( 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.jpg Hans Spemann.jpg John Gurdon.jpg
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".


  1. R Briggs, T J King Transplantation of Living Nuclei From Blastula Cells into Enucleated Frogs' Eggs. Proc. Natl. Acad. Sci. U.S.A.: 1952, 38(5);455-63 PubMed 16589125 | PMC1063586 | PNAS Classic
  2. Christoph Waldner, Magdalena Roose, Gerhart U Ryffel Red fluorescent Xenopus laevis: a new tool for grafting analysis. BMC Dev. Biol.: 2009, 9;37 PubMed 19549299 | PMC2706234 | BMC Dev Biol.
  3. Natalia Sáenz-Ponce, Christian Mitgutsch, Eugenia M del Pino Variation in the schedules of somite and neural development in frogs. Proc. Natl. Acad. Sci. U.S.A.: 2012, 109(50);20503-7 PubMed 23184997
  4. Alexander A Tokmakov, Sho Iguchi, Tetsushi Iwasaki, Yasuo Fukami Unfertilized frog eggs die by apoptosis following meiotic exit. BMC Cell Biol.: 2011, 12;56 PubMed 22195698
  5. Anna Kosubek, Ludger Klein-Hitpass, Katrin Rademacher, Bernhard Horsthemke, Gerhart U Ryffel Aging of Xenopus tropicalis eggs leads to deadenylation of a specific set of maternal mRNAs and loss of developmental potential. PLoS ONE: 2010, 5(10);e13532 PubMed 21042572
  6. Thiagarajan Venkatarama, Fangfang Lai, Xueting Luo, Yi Zhou, Karen Newman, Mary Lou King Repression of zygotic gene expression in the Xenopus germline. Development: 2010, 137(4);651-60 PubMed 20110330
  7. M Kloc, G Spohr, L D Etkin Translocation of repetitive RNA sequences with the germ plasm in Xenopus oocytes. Science: 1993, 262(5140);1712-4 PubMed 7505061
  8. Samantha A Morris, Alexandra D Almeida, Hideaki Tanaka, Kunimasa Ohta, Shin-ichi Ohnuma Tsukushi modulates Xnr2, FGF and BMP signaling: regulation of Xenopus germ layer formation. PLoS ONE: 2007, 2(10);e1004 PubMed 17925852 | PMC1994590 | PLoS ONE
  9. 9.0 9.1 Wanzhou Hu, Nasrin Haamedi, Jaehoon Lee, Tsutomu Kinoshita, Shin-ichi Ohnuma The structure and development of Xenopus laevis cornea. Exp. Eye Res.: 2013, 116;109-28 PubMed 23896054 | Exp Eye Res.
  10. Christina James-Zorn, Virgilio G Ponferrada, Chris J Jarabek, Kevin A Burns, Erik J Segerdell, Jacqueline Lee, Kevin Snyder, Bishnu Bhattacharyya, J Brad Karpinka, Joshua Fortriede, Jeff B Bowes, Aaron M Zorn, Peter D Vize Xenbase: expansion and updates of the Xenopus model organism database. Nucleic Acids Res.: 2013, 41(Database issue);D865-70 PubMed 23125366


Rugh 1951.jpg

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

Frog Development (1951): Introduction | Rana pipiens | Reproductive System | Fertilization | Cleavage | Blastulation | Gastrulation | Neurulation | Early Embryo Changes | Later Embryo or Larva | Ectodermal Derivatives | Endodermal Derivatives | Mesodermal Derivatives | Summary of Organ Appearance | Glossary | Bibliography | Figures


Teruo Kaneda, Jun-ya Doi Motoki Gastrulation and pre-gastrulation morphogenesis, inductions, and gene expression: similarities and dissimilarities between urodelean and anuran embryos. Dev. Biol.: 2012, 369(1);1-18 PubMed 22634398

C Michael Jones, James C Smith An overview of Xenopus development. Methods Mol. Biol.: 2008, 461;385-94 PubMed 19030813

Eugenia M del Pino, Michael Venegas-Ferrín, Andrés Romero-Carvajal, Paola Montenegro-Larrea, Natalia Sáenz-Ponce, Iván M Moya, Ingrid Alarcón, Norihiro Sudou, Shinji Yamamoto, Masanori Taira A comparative analysis of frog early development. Proc. Natl. Acad. Sci. U.S.A.: 2007, 104(29);11882-8 PubMed 17606898

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