Histogenesis of the upper jaw teeth in gobiid fish, Sicyopterus macrostetholepis

Yoshiko KAKIZAWA

Department of Anatomy,
Nihon University School of Dentistry
Tokyo 101, JAPAN


　　　Introduction

　Sicyopterus macrostetholepis belongs to the genus Sicyopterus of the family Gobiidae and is closely related to Sicyopterus japonicus.1)
　The structure of the upper jaw teeth of Sicyopterus macrostetholepis 5) are characteristic shape suitedto scraping off diatoms on stones similar to those of Sicyopterus japonicus.5),7),9) Each functional tooth has many successional teeth behind it, so it has the advantage of observing various developmental stages of the enameloid formation.
　The author observed precisely about the histogenesis of the upper jaw teeth of Sicyopterus macrostetholepis and gained some informations of the enameloid　formation as follows.


　　　Materials and methods

　Four fish were used for this study. Two fish (78 and 45mm in total lengths) were captured on 4th of May in 1979 at the Arakawa river, Ishigaki city, Okinawa prefecture, Japan. They were given by courtesy of Mr. Masayoshi Hayashi.
　Another two fish (70 and 90mm in total lengths) were captured on 7th of October in 1990 at the same river. They were offered by courtesy of Mr. Akihisa Iwata.
　The specimens were fixed in ten percent neutral formalin and some were demineralized in ten percent EDTA, dehydrated in ethanol, cleared in xylene and embedded in paraffin.
　The sagittal and horizontal serial sections were cut at six microns, deparaffinzied in xylene,
stained with Hematoxylin-Eosin, Masson-Goldner, PAS reaction, Toluidin blue and Prussian blue
and examined by the light microscopy. The half of the specimen of 45mm fish was prepared for the scanning electron microscopy and examined by SEM.

　　　Results

1) Scanning electron microscope observation

　The functional teeth (FT) of the upper jaw teeth were located on the outside of the premaxillary bone (PM) lined up in a row.1) Behind each functional tooth, there were many successional teeth (ST) enclosed with the capsule (C) of connective tissues. From the labial side towards the backward, the successional teeth were densely existed, but at the rear side of　capsule (Fig.1 arrow) they reversed to the direction and the number of teeth were decreased (Fig.1).
　The crown of functional tooth was covered with the enameloid (E) and the tip of the enameloid was divided into three, the central part had a slightly narrow width while the outer two parts were both about equally wide, and the length of three parts were equal (Fig.2). On the other hand, the enameloid of the immediately before functional tooth (ST.1) was tricuspid (Fig.3 arrow), the middle part was shorter and pointed at the tip, and those on both sides were longer and wider than middle one (Fig.3).


2) Histological observation

　The development of the tooth germ of the upper jaw teeth began to start at the tip of the dental lamina (DL) formed by invagination of the oral epithelium (Fig.4). After the basal layer cells of the oral epithelium differentiated into an inner and an outer enamel epithelium, the inner enamel epithelium (IE) was invaded gradually and the mesenchymal cells concentrated to the invagination place and formed the dental papilla (DP) (Fig.5-1). Soon the inner enamel epithelium initiated to elongate their lengths, the superficial cells of the dental papilla began to differentiate into odontoblasts (OD) (Fig.5-2). The height of the inner enamel epithelium grew more and more and odontoblasts began to secrete enameloid matrix, then the height of the tooth germ incresed gradually (Fig.5-2,3,4).
　As soon as the enameloid matrix formation was finished (Fig.6-1), odontoblasts began to secrete dentin matrix continuously (Fig.6-2), then the mineralization occurred and spread in both dentin and enameloid (Fig.6-3). During the first mineralization stage the height of the inner enamel epithelium became the tallest (Fig.6-2,3,4).
　Just after the first mineralization spread through enameloid and dentin (Fig.7-1), the inner
enamel epithelium secreted rather big granules (Fig.7-2 arrow, Fig.8 arrow). They were well stained with eosin and fuchsin-ponceau de xylidin. In accordance with this stage the peculiar strructure began to be able to discern between dentin and enameloid (Fig.7*). It was triangular region (Fig.7*) and remained demineralized (Fig. 9*).
　When the enameloid was highly mineralized, smaller granules were found in the inner enamel epithelium (Fig.9 arrow). Further in the enameloid maturation stage, the similar fine granules were found in the tips of the inner enamel epithelium (Fig.10, 11 arrow) and they were stained yellow-brown with Hematoxylin-Eosin and dark-blue with Prussian blue.
　About the time when the enameloid was completed, the successional teeth turned round and went forward the labial side (Fig.12). The completed enameloid showed brilliant yellow-brown color accompanying some structure (Fig.13*) on the border of dentin.

　　　Discussion

1) The enameloid formation stage

　In the histogenesis of the upper jaw teeth it was most characteristic that the enameloid formation stage was very long. For example of 45 successional teeth (70mm fish), 40　successional teeth were enameloid formation stage and 5 were root-dentin and pedicle formation stage 4). In the numbers of 40 successional teeth the ratio of the enameloid matrix formation stage to the enameloid mineralization and maturation stage was 6:34. So it was clear that the enameloid mineralization and maturation stages were long and complicated stages.

2) The granules of the mineralization and maturation stages

　 Three different granules were observed in the long term of mineralization and maturation stages. At the first mineralization stage, the rather big granules were observed between the inner enamel epithelium and enameloid (Fig.7,8). In the highly mineralization and maturation stages smaller fine granules were found in the inner enamel epithelium (Fig.9,10, 11). Especially the granules of the maturation stage were stained heavily with Prussian blue (Fig.11), so they were almost certained to be the ferritin granules 8).
　Thinking of these granules secreted by the inner enamel epithelium, it was suggested that the inner enamel epithelium concerned in the enameloid mineralization.

3) The intermediate region

　The staining of the matrix of the enameloid and dentin showed mesodermal origin, so they
seemed to be secreted by odontoblasts 6). Different from the enameloid matrix of Oplegnathus
fasciatus3), there were no conspicuous matrix fiber bundles in the enameloid, but in the dentin tubule-like structures were observed like Oplegnathus fasciatus 3). The peculiar structure between dentin and enameloid (Fig.7,9,10,12,13*) showed different staining from enameloid, resisted against demineralization and had no tubule-like structures, so it was neither enameloid nor dentin and considered to be the transitional area as Everett 2) observed in Squalus acanthius.

References

1) Akihito, Prince and Megro, K,: On the differences between the genera Sicydium and Sicyopterus
(Gobiidae). Japan J. Ichtyol. 26, 192-202, 1979.
2) Everett, M. and Miller, W. : Histochemistry of lower vertebrate calcified structures. I. Enamel of the dogfish Squalus acanthius compared with mammalian enamel and homologous dentine. J. Morph. 170, 95-111, 1981
3) Isokawa, S., Yoshida, M., Ikeda, K., Yamaguchi, K., Chikazawa, N. and Fujioka, S. : Tooth
enameloid formation of a fish-chronological relationship of matrix formation and mineralization of the enameloid and dentin. J. Nihon Univ. Sch. Dent. 14, 1-15, 1972.
4) Kakizawa, Y., Saito, N., Shimada, M., Kanematsu, Y., Yi, J. and Toda, Y. : Study of the upper jaw teeth of the gobiid fish, Sicyopterus macrostetholepis. Nihon Univ. Dent. J. 68, 626-632, 1994.
5) Kakizawa, Y., Kajiyama, N., Nagai, K., Kado, K., Fujita, M., Kashiwaya, Y., Imai, C., Hirama, A., and Yorioka, M. : The histological structure of the upper and lower jaw teeth in the gobiid fish, Sicyopterus japonicus. J. Nihon Univ. Sch. Dent. 28, 175-187, 1986.
6) Kvam, I.: On the development of dentin in fish. I. Squalus acanthias Linnaeus. J.Dent Res. 32,
280-286, 1953.
7) Mochizuki, K. and Fukui, S. :Development of upper jaw teeth in gobiid fish, Sicyopterus　japonicus. Japan J. Ichtyol. 30, 27-36, 1983.
8) Sasagawa, I. : Iron accumulation in the dental epithelial cell of Tilapia nilotica, a teleost. ACBTE, 3, 19-28, 1993.
9) Yorioka, M. : The eruption and shedding of upper jaw teeth in gobiid fish, Sicyopterus japonicus. Nihon Univ. Dent. J. 62, 29-34,1988.

Explanation of figures :


{　Sorry, Figures will be installed soon }


Fig. 1 :
SEM of the upper jaw teeth X50
FT : functional teeth　　ST : successional teeth　　
PM : premaxillary bone　 C : capsule

Fig. 2 :
SEM of the crown of functional tooth X250
E : enameloid

Fig. 3 :
SEM of the tricuspid enameloid X100
ST.1 : successional tooth immediately before functional tooth
FT : functional tooth

Fig. 4 :
Initiation of tooth development. demineralized sagittal section, H-E X500
DL : dental lamina

Fig. 5 :
Enameloid matrix formation stage. demineralized sagittal section, H-E X500
I E : inner enamel epithelium　OE : outer enamel epithelium
DP : dental papilla　OD : odontoblast
E : enameloid matrix

Fig. 6 :
Enameloid first mineralization stage. sagittal section, H-E stain X200
E : enameloid　D : dentin

Fig. 7 :
The granules shown just after the first mineralization stage. sagittal section, H-E X200

Fig. 8 :
Magnification of the granules in the same stage of Fig.7. demineralized sagittal section, H-E X500

Fig. 9 :
Enameloid highly mineralization stage. demineralized sagittal section, H-E X500

Fig.10 :
Enameloid maturation stage. sagittal section , H-E X240

Fig.11 :
The granules of the tip of inner enamel epithelium in maturation stage.Prussian blue
X300

Fig.12 :
The enameloid turned round towards the labial side. sagital section, H-E X150

Fig.13 :
The completed enameloid in successional teeth. sagittal section, H-E X500
E : enameloid　D : dentin