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Embryonic Development and Organogenesis of Chinese Giant Salamander , Andrias Davidianus ＊

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Embryonic Development and Organogenesis of Chinese Giant Salamander , Andrias Davidianus ＊ PROGRESS IN NATURAL SCIENCE Vol .17 , N o .11 , November 2007 Embryonic development and organogenesis of Chinese giant salamander , Andrias davidianus ＊ Luo Jian＊＊ , Xiao Yamei ＊＊ , Luo Kaikun , Huang Xiaoxi , Peng Liangy ue , Liu Yun＊＊＊ (Key Laboratory of Protein C hemistry and Fish Developmental Biology of National Education Ministry , College of Life Sciences, Hunan Normal University , Changsha 410081 , China) Accepted on May 8 , 2007 Abstract The morphology and organogenesis of Chinese giant salamander , An drias david ianus, in its different developmental periods and stages are described in detail, w hich provides an intact criterion for distinguishing different stages of its developmental process. Based on the external morphological and internal histological features, six periods including 20 stages of organogenesis of Chinese giant salamander are established , which are cleavage period , blastula period , gastrula period, neurula period , organogenesis stage and hatching stage.Generally , the embryonic development of Chinese giant salamander is consistent w ith those of Eastern new t , Cynops orientalis , and Black spots frog , R .nigromacula ta .How ever, they have some differences in the early cleavage process and the development of di- gestive system .The cleavage of Chinese giant salamander , A .david ianus is not a discoidal division type , w hich is different from other species reported .And the first three cleavages being meridional and a retardant development of its digestive system w ithout halter and sucker existing are the evident features of the emb ryonic development of Chinese giant salamander. Keywords: Chinese giant salamander, Andrias d avidianus , embryogenesis, cleavage, organogenesis. Am phibian is a transitional animal class for the has made some research progress in the artificial re- vertebrates from aquatic to terraneous , the research of production of Chinese giant salamander , with w hich a w hose embry onic development is significant for ex- continual and systematic study on its morphological ploring vertebrates' evolution and studying the com- and histological features has been carried out .I t will parative embryology .At the present time , the majo r help us understand its early cleavage and org anogene- research of amphibian embryology focuses on Anuran sis process, and finally reveal the evolution of Crypto- and Salamandra , and the study of Eastern new t , branchidae and Amphibian . Cynops orientalis , is a no table one .Cai[ 1] has estab- lished a system to distinguish different stages of the 1 Materials and methods embryonic development of Eastern new t , and illus- 1 .1 M aterials trated a series of detailed pictures of its morphology and organogenesis.And Cryptobranchidae is a group The artificial reproduction and incubation of Chi- of archaic vertebrates on the edge of depopulation[ 2] , nese giant salamander were carried out at Base of Ar- among w hich are North American hellbender (Cryp- tificial Reproduction of Chinese Giant Salamander , an tobranchus), Japanese giant salamander (Andrias affiliated agency to our lab .At first , the sex ually ma- japonicus), and Chinese giant salamander (Andrias tured parents were treated w ith artificial reproduction davidianus).There are no publications about the to get the matured egg s and sperms , then the fertil- embryonic development of North American hellbender ized eggs w ere obtained by artificial insemination . and Japanese giant salamander , but some embryonic Then the fertilized egg s were hatched by incubating studies have been carried out on Chinese giant sala- in flowing w ater in the incubation pools (tem perature mander , although the study is limited and restricted 20 ±1 ℃, concentration of dissolved oxygen 5 ±1 to primary observation of embryonic appearance , and mg/L , pH 7 .4 —7 .6).The illumination time was the stage disting uishing system is obscure w ith a lack- about one hour per day (exposure rate , 4 1x). [ 3 —5] ing of organogenesis study .Recently , our lab ＊ S upported by National Natu ral Science Foundation of C hina (Grant Nos.30450006)and Hunan Provincial Education Department (06B055) ＊＊ These authors contributed equally to this w ork . ＊＊＊ To w hom correspondence should be addressed .E-mail:Liuyun @hunnu .edu .cn 1304 www .tandf .co .uk/ journals Progress in N atural Science V ol.17 No .11 2007 1 .2 Methods (Continued) Time after The methods fo r observing and recording mor- Periods S tages fertilization Characteristics (h) phological features are as follow s .Fo r the embryos between fertilization and multi-cell stage , the obser- Late blastula 90 —128 Expanded blastocoel w ith 2 — 3 layers of cells on the top vation and report were made every 2 hours .For the Gastrula Early gastrula 128 —172 Dorsal lip embryos betw een blastula stage and tail bud stage , Middle gastrula 172 —216 Expanded archenteric cavity the observation and report were made every 8 hours . and lateral lip For the em bryos betw een branchia plate stage and Late gastrula 216 —240 Disappearance of blastocoel hatching stage , the observation and report w ere made and yolk plug formation every 12 hours.Each embry onic developmental stage Neu rula Neural plate 240 —256 Neural plate and primary w as decided by the time w hen more than a half of the body cavity embryos w ere in the same stage .To tally about 1100 Neural folds 256 —280 Neural fold and somites embryos were mo rphologically studied from year 2003 Neural tube 280 —300 Forebrain and hindbrain dif- ferentiation , optic vehicle/ to year 2005 .The histological studies investig ated 56 pharynx/ neph ridium / intes- embryos from 1100 during the w hole embry onic de- tine velopmental process .The early embryos w ere fixed in Organogen- Tail bud 300 —356 Heart anlage and tail bud Smith' s fluid and dehydrated by ethanol and tertiary esis alcohol .The embry os after the forelimb bud stage Branchial plate 356 —412 Branchial plate and pigment in body, atrium and ventricle w ere fixed in Bouin' s solution and dehydrated by differentiation ethanol.All the embryonic sam ples were embedded in Early forelimb 412 —468 Auditory vesicle/ diencephalons/ paraffin , sectioned (6 —10 μm), and stained with bud rhomb encephalon/ branchial hem atoxylin-eosin .Nikon SMZ800 and Oly mpus branches/ liver/ forelimb , XTL-Ⅱ stereoscope sy stems were used to investig ate beating heart, dorsal chorda vacuolization the ex terior appearance of the early embryos , and a Late forelimb 468 —516 Lens / olfactory pit/ thyroid Sony R1 digital camera w as used to take pictures .Fo r bud gland tissue sections , micrographs were taken by a Nikon Early branchia- 516 —540 Eye pigment/ branchia-circu- E600 micro-pho tographic shoo t system . circulation lation , transparent ventral vessel networks The distinguishing of the embryo nic develop- Late branchia- 540 —596 Increased branchial branches, mental stages of Chinese giant salamander was based circulation mandible/stomach , abundant on the morphological and histological characters refer- body pigment [ ] ring to the standard for Cynops orientalis 1 and Tail circulation 596 —676 Vitreous lens, feather-like [ 6] branchia , tail circulation , Rana nigromaculata . abundan t pigment in the ven- tral 2 Results Hatching Posterior limb 676 —768 Posterior limb bud/anus, bud dorsal skin glands The w hole process of the embry onic development of Chinese giant salamander could be divided into 6 2 .1 Cleavage period periods , w hich could be further divided into 20 stages (Table 1). The eggs of Chinese giant salamander w ere about 5 to 8 mm diametrically , with no pigment existing . T able 1. Different periods of the embryonic development of And the abundance of yolk made them yellow ish , al- Chinese giant salamander though in the nearby of the anim al pole was an under- Time after Periods Stages fertilization Characteristics tone .The egg w as w rapped by a gel envelope , w hich (h) w ould expand after hydration and m ade the periv- C leavage 2-cell 18 —22 Cleavage of fertilized egg itelline space enlarge . 4-cell 22 —26 2 cleavage grooves 8-cell 26 —30 4 cleavage grooves About 20 hours after fertilization , a cleavage Multi-cell 30 —48 Cleavage cavity g roove appeared in the animal pole , indicating the Blastula Early blastula 48 —90 Blastocoel first cleavage .The first cleavage w as a meridional (To be con tinued) one , and the cleavage g roove deepened in the animal Prog ress in Natural Science Vol.17 No .11 2007 www .tandf .co .uk/ journals 1305 pole , w hich ex tended to the plant hemisphere gradu- cleavage w as latitudinal and close to the animal pole . ally and disappeared there (Fig .1(a)).I t took about The fourth cleavage in the eight cells w as non-syn- 4 to 8 hours for the fertilized egg to finish the first chronous and irregular w ith different dividing speed cleavage .The second cleavage appeared tw o hours af- fo r each cell .The cleavages happened every 2 to 4 ter the appearance of the first before it finished .And hours in the early developmental time , w hose speeds the second cleavage was also meridional , vertical to were quickened gradually in the follow ing develop- the first one (Fig .1(b)).The third cleavage w as ment .Subsequently , a thickly-woven groove of cleav- meridio nal too , and the two cleavage grooves were ages appeared in the anim al hemisphere , w ith only mutually vertical, making the eight cells in the early several being distinguished in the plant hemisphere . embryo look like a sign of (Fig .1(c)).The fourth 1306 www .tandf .co .uk/ journals Progress
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