Some Recent Findings
- The axolotl genome and the evolution of key tissue formation regulators "Salamanders serve as important tetrapod models for developmental, regeneration and evolutionary studies. An extensive molecular toolkit makes the Mexican axolotl (Ambystoma mexicanum) a key representative salamander for molecular investigations. Here we report the sequencing and assembly of the 32-gigabase-pair axolotl genome using an approach that combined long-read sequencing, optical mapping and development of a new genome assembler (MARVEL). We observed a size expansion of introns and intergenic regions, largely attributable to multiplication of long terminal repeat retroelements. We provide evidence that intron size in developmental genes is under constraint and that species-restricted genes may contribute to limb regeneration. The axolotl genome assembly does not contain the essential developmental gene Pax3. However, mutation of the axolotl Pax3 paralogue Pax7 resulted in an axolotl phenotype that was similar to those seen in Pax3-/- and Pax7-/- mutant mice." Pax
- Morphological and transcriptomic analyses reveal three discrete primary stages of postembryonic development in the common fire salamander, Salamandra salamandra "The postembryonic development of amphibians has been characterized as divided into three predominant periods, hereafter named primary developmental stages: premetamorphosis (PreM), prometamorphosis (ProM), metamorphic climax (Meta), and completion of metamorphosis (PostM), largely based on examination of anuran development. ...Our results support that primary stages of postembryonic development in caudates are homologous to those of anurans, and offer a baseline for the study of the evolution of developmental modes."
- Dual embryonic origin and patterning of the pharyngeal skeleton in the axolotl "The impressive morphological diversification of vertebrates was achieved in part by innovation and modification of the pharyngeal skeleton. Extensive fate mapping in amniote models has revealed a primarily cranial neural crest derivation of the pharyngeal skeleton....Our fate map confirms a dual embryonic origin of the pharyngeal skeleton in urodeles, including derivation of basibranchial 2 from mesoderm closely associated with the second heart field. Additionally, heterotopic transplantation experiments reveal lineage restriction of mesodermal cells that contribute to pharyngeal cartilage. The mesoderm-derived component of the pharyngeal skeleton appears to be particularly sensitive to retinoic acid (RA): administration of exogenous RA leads to loss of the second basibranchial, but not the first. Neural crest was undoubtedly critical in the evolution of the vertebrate pharyngeal skeleton, but mesoderm may have played a central role in forming ventromedial elements, in particular. When and how many times during vertebrate phylogeny a mesodermal contribution to the pharyngeal skeleton evolved remain to be resolved."
| More recent papers
This table shows an automated computer PubMed search using the listed sub-heading term.
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Search term: Axolotl Development
Alexey G Desnitskiy Cell cycles during early steps of amphibian embryogenesis: a review. BioSystems: 2018; PubMed 30240720
Paul Lukas, Lennart Olsson Bapx1 is required for jaw joint development in amphibians. Evol. Dev.: 2018; PubMed 30168254
Duygu Payzin-Dogru, Jessica L Whited An integrative framework for salamander and mouse limb regeneration. Int. J. Dev. Biol.: 2018, 62(6-7-8);393-402 PubMed 29943379
Paul Lukas, Lennart Olsson ##Title## Zoological Lett: 2018, 4;16 PubMed 29942645
Katherine Brown An interview with Elly Tanaka. Development: 2018, 145(11); PubMed 29884656
| Older papers
- Stochastic specification of primordial germ cells from mesoderm precursors in axolotl embryos "A common feature of development in most vertebrate models is the early segregation of the germ line from the soma. For example, in Xenopus and zebrafish embryos primordial germ cells (PGCs) are specified by germ plasm that is inherited from the egg; in mice, Blimp1 expression in the epiblast mediates the commitment of cells to the germ line. How these disparate mechanisms of PGC specification evolved is unknown. Here, in order to identify the ancestral mechanism of PGC specification in vertebrates, we studied PGC specification in embryos from the axolotl (Mexican salamander), a model for the tetrapod ancestor. In the axolotl, PGCs develop within mesoderm, and classic studies have reported their induction from primitive ectoderm (animal cap). We used an axolotl animal cap system to demonstrate that signalling through FGF and BMP4 induces PGCs. The role of FGF was then confirmed in vivo. We also showed PGC induction by Brachyury, in the presence of BMP4. These conditions induced pluripotent mesodermal precursors that give rise to a variety of somatic cell types, in addition to PGCs. Irreversible restriction of the germ line did not occur until the mid-tailbud stage, days after the somatic germ layers are established. Before this, germline potential was maintained by MAP kinase signalling. We propose that this stochastic mechanism of PGC specification, from mesodermal precursors, is conserved in vertebrates."
- Regeneration of Limb Joints in the Axolotl "In spite of numerous investigations of regenerating salamander limbs, little attention has been paid to the details of how joints are reformed. An understanding of the process and mechanisms of joint regeneration in this model system for tetrapod limb regeneration would provide insights into developing novel therapies for inducing joint regeneration in humans. To this end, we have used the axolotl (Mexican Salamander) model of limb regeneration to describe the morphology and the expression patterns of marker genes during joint regeneration in response to limb amputation. These data are consistent with the hypothesis that the mechanisms of joint formation whether it be development or regeneration are conserved. We also have determined that defects in the epiphyseal region of both forelimbs and hind limbs in the axolotl are regenerated only when the defect is small. As is the case with defects in the diaphysis, there is a critical size above which the endogenous regenerative response is not sufficient to regenerate the joint. This non-regenerative response in an animal that has the ability to regenerate perfectly provides the opportunity to screen for the signaling pathways to induce regeneration of articular cartilage and joints."
- Multiple sequences and factors are involved in stability/degradation of Awnt-1, Awnt-5A and Awnt-5B mRNAs during axolotl development. "Following fertilization in amphibian, early cleavage stages are maternally controlled at a post-transcriptional level before initiation of zygotic transcriptions at the mid blastula transition (MBT). ...Altogether, these results show that oocyte maturation and late cleavages following MBT are two important periods when axolotl Wnt RNAs are highly regulated."
- The axolotl limb: a model for bone development, regeneration and fracture healing. "Among vertebrates, urodele amphibians (e.g., axolotls) have the unique ability to perfectly regenerate complex body parts after amputation."
- Expression of heat-shock protein 70 during limb development and regeneration in the axolotl. "Using molecular biology and biochemical techniques, we have characterized both the spatiotemporal and quantitative expression patterns of Hsp-70 in axolotl development and regeneration. Our results show that Hsp-70 is expressed and regulated during axolotl development as in other vertebrates. Our data also demonstrate an up-regulation of the RNA transcript for Hsp-70 during limb regeneration as early as 24 hr after amputation that is maintained up to early differentiation. We also demonstrate a similar pattern of expression for the protein during regeneration. Finally, we show that axolotl Hsp-70 is induced threefold after heat-shock as observed in other vertebrates."
The following stage information is based upon published staging data.
|| Freshly laid egg in jellycoat.
|| First appearance of the first cleavage furrow and the animal pole.
|| Four cells.
|| Eight cells.
|| 16 cells.
|| 6.5 - 7
|| 32 cells
|| 8 - 9
|| 64 cells
|| Early blastula (fall of mitotic index in animal blastomeres).
|| Late blastula, surface is smooth.
|| Early gastrula I, first sign of dorsal blastopore lip.
|| Middle gastrula II, Blastopore covers three quadrants. Lateral lips are formed; ventral lip is marked only by pigment accumulation. Yolk plug reaches its maximum diameter.
|| Late gastrula II, Blastopore has an oval or circular shape.
|| Early neurula II: Neural plate is broad. Neural folds are outlined and begin to rise above the surface in the head region. Embryo is slightly elongated.
|| 59 - 63
|| Early neurula III and middle neurula: Neural plate is shield-shaped and becomes sunken; neural folds are raised and bound all regions of the neural plate.
|| Late Neurula I: Neural folds are higher; especially in the head region. Further narrowing and deepening of the neural plate occur both in the head and in the spinal regions. Hyomandibular furrow limiting the mandibular arch is slightly outlined. The segmentation of the mesodermal material begins. There are two pairs of somites.
|| Late neurula II: Neural plate is deeply sunken. Neural folds are closing and are especially high in the head region where three slight bulges corresponding to fore-, mid- and hindbrain vesicles are outlined. The neural folds of the spinal region are almost in contact. Hyomandibular furrow is more marked. There are two pairs of somites.
|| Late neurula III: Neural folds are in contact throughout, but are not yet fused. Brain curvature is quite distinct in profile; fore-, mid- and hindbrain vesicles are also distinct. The swelling of optic vesicles is outlined (barely visible in these pictures because of unfortunate perspective). Hymandibular furrows are deeper. There are three pairs of somites.
|| Late Neurula IV: Späte Neurulation IV: Neural folds are fused in spinal region (or are starting this process in these pictures); in brain region, they are only in contact. Optical vesicles are destinct and becoming larger. Grooves in ectoderm appear at the level of the hindbrain. A very slight swelling marks the future gill region. Mandibular arch becomes prominent and four pairs of somites are present.
|| Neural folds are completely fused. The gill region and the pronephros are distinct; the tailbud is slightly outlined. Five to six pairs of somites are present. Primordium of the ear is outlined as a shallow depression in the ectoderm in the region above the future hyoid arch. The hyobranchial furrow appears, outlining the boundary between the hyoid arch and the first branchial arch.
|| Ear pit is outlined and becomes more distinct. The hyobranchial furrow lengthens ventrally. The prophenic swelling is clearly outlined, and both the pronephros itself and the beginning of the pronephric duct are clearly visible Eight or nine pairs of somites are visible.
|| Since first cleavage, up to 97 hours have passed (sorry, I missed some hours here... ;-) ). Ear pit becomes quite distinct. The gill region is clearly outlined. The pronephric duct is clearly visible along six somites at least. The primordium of the olfactory organ appears as a tubercle on the anterior part of the head; the tailbud is gradually enlarging in all stages. Up to 16 pairs of somites are present.
|| The body of the embryo continues to straighten; the tailbud enlarges. Dorsal finfold begins at somite 14-12. A groove appears in the region of the lens primordium (visual system - i.e. eyes) The third branchial furrow becomes apparent in the dorsal part of the gill region.
|| The dorsal fin develops until it begins at somite 10.
|| From this stage on, the body axis from the hindbrain to the tail base are quite straight. Three external gills show ad nodules on the surface of the gill swelling. The lateral line reaches to the sixth somite. The dorsal fin begins at the fifth somite. The first chromatophores appear; heart pulsation begins.
|| Gills elongate and push venventroposteriorly. No limb buds are yet visible.
|| Filament sprouts appear as two nodules on each gill. The primordium of the operculum is visible as a fold upon the hyoid arch. Neither of the two rudiments of the perculum reaches the midline. The limb buds are slightly outlined.
|| The first gills have two pairs of filament sprouts; the second and third have three pairs each. The gills cover the limb buds. Both rudiments of the operculum approach the midline. The angle of the mouth begins to show.
|| The gills are longer and the number of filaments increases (four pairs in the first gills, six or seven pairs on the second or third gills). The rudiments of the operculum join at the middline. The angles of the mouth are marked more distinctly and limb buds protrude slightly.
|| The gills contunie to elongate, the number of filaments increases and they become longer. The mouth is distinctly outlined. The second lateral line runs along the flank toward the limb bud and bypasses it on the ventral side. Hatching begins.
|| The gills extend far beyond the forelimb buds. The mouth is completely outlined, but is not broken through.
|| With galvanic and convulsive movements the larva breaks free of the jelly coat. The mouth either is already opened or will open within the next 24 - 72 hours.
Thyroid Hormone Effects
| The effect of thyroxine on the early larval development of the axolotl. The same control and 30 nM T4-treated (TH) sibling animals were photographed at the days postfertilization noted. T4 was added from day 14. (Bar = 1 cm.)
Axolotl developing limb Bmp2 and Sox9 expression and cartilage staining.
A study has used the axolotl as a model for tooth development. Using transgenic axolotls and fate-mapping approaches they found "evidence of oral teeth derived from both the ectoderm and endoderm and, moreover, demonstrate teeth with a mixed ecto/endodermal origin. Despite the enamel epithelia having a different embryonic source, oral teeth in the axolotl display striking developmental uniformities and are otherwise identical. This suggests a dominant role for the neural crest mesenchyme over epithelia in tooth initiation and, from an evolutionary point of view, that an essential factor in teeth evolution was the odontogenic capacity of neural crest cells, regardless of possible 'outside-in' or 'inside-out' influx of the epithelium."
Axolotl brain ventricular zone proliferative activity
Prophases of the Heterotype Division in the Male Axolotl
The maturation divisions in the female (Axolotl)
Development of the optic cup and lens in Siredon pisciformis
- ↑ 1.0 1.1 Bordzilovskaya NP, Dettlaf TA, Duhan ST, Malacinski GM: Developmental-stage series of axolotl embryos. In Developmental Biology of the Axolotl. Edited by: Armstrong JB, Malacinski GM. New York: Oxford University Press; 1989:201-219.
- ↑ Nowoshilow S, Schloissnig S, Fei JF, Dahl A, Pang AWC, Pippel M, Winkler S, Hastie AR, Young G, Roscito JG, Falcon F, Knapp D, Powell S, Cruz A, Cao H, Habermann B, Hiller M, Tanaka EM & Myers EW. (2018). The axolotl genome and the evolution of key tissue formation regulators. Nature , 554, 50-55. PMID: 29364872 DOI.
- ↑ Sanchez E, Küpfer E, Goedbloed DJ, Nolte AW, Lüddecke T, Schulz S, Vences M & Steinfartz S. (2018). Morphological and transcriptomic analyses reveal three discrete primary stages of postembryonic development in the common fire salamander, Salamandra salamandra. J. Exp. Zool. B Mol. Dev. Evol. , , . PMID: 29504232 DOI.
- ↑ Sefton EM, Piekarski N & Hanken J. (2015). Dual embryonic origin and patterning of the pharyngeal skeleton in the axolotl (Ambystoma mexicanum). Evol. Dev. , 17, 175-84. PMID: 25963195 DOI.
- ↑ Chatfield J, O'Reilly MA, Bachvarova RF, Ferjentsik Z, Redwood C, Walmsley M, Patient R, Loose M & Johnson AD. (2014). Stochastic specification of primordial germ cells from mesoderm precursors in axolotl embryos. Development , 141, 2429-40. PMID: 24917499 DOI.
- ↑ Lee J & Gardiner DM. (2012). Regeneration of limb joints in the axolotl (Ambystoma mexicanum). PLoS ONE , 7, e50615. PMID: 23185640 DOI.
- ↑ Caulet S, Pelczar H & Andéol Y. (2010). Multiple sequences and factors are involved in stability/degradation of Awnt-1, Awnt-5A and Awnt-5B mRNAs during axolotl development. Dev. Growth Differ. , 52, 209-22. PMID: 20151991 DOI.
- ↑ Hutchison C, Pilote M & Roy S. (2007). The axolotl limb: a model for bone development, regeneration and fracture healing. Bone , 40, 45-56. PMID: 16920050 DOI.
- ↑ Lévesque M, Guimond JC, Pilote M, Leclerc S, Moldovan F & Roy S. (2005). Expression of heat-shock protein 70 during limb development and regeneration in the axolotl. Dev. Dyn. , 233, 1525-34. PMID: 15965983 DOI.
- ↑ Brown DD. (1997). The role of thyroid hormone in zebrafish and axolotl development. Proc. Natl. Acad. Sci. U.S.A. , 94, 13011-6. PMID: 9371791
- ↑ Guimond JC, Lévesque M, Michaud PL, Berdugo J, Finnson K, Philip A & Roy S. (2010). BMP-2 functions independently of SHH signaling and triggers cell condensation and apoptosis in regenerating axolotl limbs. BMC Dev. Biol. , 10, 15. PMID: 20152028 DOI.
- ↑ Soukup V, Epperlein HH, Horácek I & Cerny R. (2008). Dual epithelial origin of vertebrate oral teeth. Nature , 455, 795-8. PMID: 18794902 DOI.
Maden M. (2008). Axolotl/newt. Methods Mol. Biol. , 461, 467-80. PMID: 19030817 DOI.
Roy S & Gatien S. (2008). Regeneration in axolotls: a model to aim for!. Exp. Gerontol. , 43, 968-73. PMID: 18814845 DOI.
Frost-Mason SK & Mason KA. (1996). What insights into vertebrate pigmentation has the axolotl model system provided?. Int. J. Dev. Biol. , 40, 685-93. PMID: 8877441
Epperlein HH, Löfberg J & Olsson L. (1996). Neural crest cell migration and pigment pattern formation in urodele amphibians. Int. J. Dev. Biol. , 40, 229-38. PMID: 8735933
Simon HG. (2012). Salamanders and fish can regenerate lost structures--why can't we?. BMC Biol. , 10, 15. PMID: 22369645 DOI.
Caulet S, Pelczar H & Andéol Y. (2010). Multiple sequences and factors are involved in stability/degradation of Awnt-1, Awnt-5A and Awnt-5B mRNAs during axolotl development. Dev. Growth Differ. , 52, 209-22. PMID: 20151991 DOI.
Hutchison C, Pilote M & Roy S. (2007). The axolotl limb: a model for bone development, regeneration and fracture healing. Bone , 40, 45-56. PMID: 16920050 DOI.
Lévesque M, Guimond JC, Pilote M, Leclerc S, Moldovan F & Roy S. (2005). Expression of heat-shock protein 70 during limb development and regeneration in the axolotl. Dev. Dyn. , 233, 1525-34. PMID: 15965983 DOI.
Nye HL, Cameron JA, Chernoff EA & Stocum DL. (2003). Extending the table of stages of normal development of the axolotl: limb development. Dev. Dyn. , 226, 555-60. PMID: 12619140 DOI.
Meuler DC & Malacinski GM. (1985). An analysis of protein synthesis patterns during early embryogenesis of the urodele--Ambystoma mexicanum. J Embryol Exp Morphol , 89, 71-92. PMID: 4093754
Signoret J. (1980). Evidence of the first genetic activity required in axolotl development. Results Probl Cell Differ , 11, 71-4. PMID: 7444204
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