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The Golgi apparatus in the developing tooth with special reference to polarity.

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S I X FIGURES
The coiistaiit arid regularly polarized coiitlitioii of the Golgi
apparatus in many t y l m of epithelial aiid glanclular cells led
Golgi and C’ajal to suggest the l)ossibility of using structure
as ail indicator of secretory polarity. (’owdry was one of the
first to apply this suggestion when h e made a study of the
mechariism of seci.etioii in the thyroid gland. B y using the
Golgi apparatus as ail indicator of secretory polarity hc
found that some of the cells secreted directly into the blood
stream while others emptied their secretion into tlie lurneii
of the follicles. Unhappily, this aiid similar studies, in which
the Oolgi apparatus has been usctl to iiidicate a revcrsal in
direction of secretion, have riot beeii g e i ~ r a l l yconfirmed aiid
some writers have even expressed doubt as to the advisahilit:of ever using the Golgi apparatus a s an indicator of physiological polarity.
In view of the increased efforts to use the Golgi ap1)aratus
as a morphological iiidicator of different physiological states
of the cell, it seems that tlie developing tooth, particular1:the eiiairiel organ, might off‘er cxccllent material to test the
hypothesis that the Golgi apparatus is a n indicator of secrctory polarity. It is well known that the amelohlasts reverse
their polarity just preceding the formation of eiiamel. Accordingly, it would be of coiisiderable importance t o determine whether or not the Qolgi apparatus reverses its position concomitantly with the other cytological structures of
the cell.
“9
30
zr. w.
BEAMS AND R. L. KIKG
X I A T E H I A L AKII XETHOTIS
The material for this stucly consists of the developing niolai*
teeth of rats, 1 to 5 days old. F o r general histological and
cytological studics tlie lower jam was fixed in Zenker’s
Hellcy ’ s , Bouin ’ s , and Fleimning ’s fluids, the11 stained in
Delatfield’s and Heidenhain’s liematoxylin. It was unnecessary to decalcify the tissue following fixation f o r 1 week
in Bouin’s fluid. F o r a study of the Golgi apparatus S a s sonov’s method proved successful. Ti1 some cases tlie niitochondria were also impregnated following Kassoiiov’s method
and were consistently revealed after tlic inethotl of Regaud.
It was unnecessary in the Nassonov arid Regaud techniques to
employ a special decalcifying fluid.
1)ESCItIPTIOiY
Since the general embryology of the teeth is so m7ell linowii
it will be unrieccssary f o r us t o review it at length here. It
will suffice to point out that the teeth have a dual embryological origin, the enamel organ being formed from the ectoclcriii
of the oral epithcliuni and the deiital papilla from the underlying mesoderm.
The enamel organ originates as a n iiivaginatioii of the epithelium which gives rise to a sac-like structure filled with
cells which are continuous with the oral epithelium. It finally
becomes isolated arid much flattened by the pushing up of the
dental papilla over which it forms a cap. The cells in contact
with the dental papilla, knowri as inner enamel cells, become
much modified in shape and size and a r e the enamel forming
portion of the orgnn. The enamel cells not in contact with the
dental papilla a r e knowii as outer enamel cells a n d are less
modified than the iiiner ones. The tissue in the iiiterior of
the enamel organ (enamel pulp cells), although ectodermal
in origin, resembles to some extent mesenchymal connective
tissue and in tlie rat contains capillaries.
The formation of enamel and dentine may be demolistrated
in the developing molar teeth of 1- to 5-day-old rats. The
enamel is deposited first a t the apex of the crown and then
GOLGI APPARATTJS IN I)ETTISI,OPINC:
mo'rf1
31
domnward toward the root of the tooth so that in an nncrupted
tooth a marked but gradual transition between the short
inactive ameloblasts and the taller active ameloblast s can be
observed. Figure 1 represents a section through such a
region, showing the striking change in size between the active
and inactive enamel forming cells. It will be recalled that
during the transition from the inactive t o the active amcloblasts the nuclei migrate from their position at the base of
the inactive ameloblast to the opposite end of the cell, i.e.,
the end directed toward the enamel pulp. I n this way the
original basal or mesenchymal end of the inactive ameloblast
has become modified as the free or discharging end of the
functional ameloblast as indicated by the laying down of
enamel. The Golgi apparatus has a net-like form in the
inactive ameloblast and is located between the nucleus and
the enamel pulp end of the cell, or, in other worcls, on the
opposite side of the nucleus from the odontoblasts and the
dental pulp (fig. 1). This position of the Golgi apparatus
is similar to that of the basal cells of the Malpighian layer
of the oral epithelium from which they have descended (fig.
3). I n those ameloblasts of the zone of changing polarity
a striking migration of the Golgi apparatus to the opposite
pole of the nucleus is observed. It will be noted that the Golgi
apparatus migrates in the form of lengthened cords or strands
along the sides of the nuclei to take up a position in the
active ameloblasts adjacent to the nucleus of the discharging
end of the cell which represents the basal end of the inactive
ameloblasts. This change in polarity of the Qolgi apparatus
is rather abrupt (fig. 1). The Golgi apparatus in the ameloblasts immediately following the reversal in polarity again
assumes a rather compact net-like structure which gradually
becomes less compact as the cells rapidly grow in height. I n
the very tall ameloblasts which a r e usually in association with
a well-developed layer of the enamel, the network of the Golgi
apparatus becomes drawn out into long anastomosing strands
which extend in some instances throughout the greater part
of the cytoplasm between the nucleus and the discharging end
H. 18. B E A M S A S l ) I:.
L. KISG
J’ig. 7 Aiiiclo1)liists i u zone of tr:iusition froiu illactire to ;wtire condition. The
position of Goigi ;ipp;ir:ittis i n :rc.tiw cclls is rewrscxl f r o m tli;it of inactire cells.
Enanicl pulp with (iolgi :ipi)ar;itus. dlolur toot11 o f r a t 1 day old. Sassoiiov
t eclin ique.
Fig. 2 Active, eloiig:ittcd iitii(~1ol)liistswith Golgi apparatus disteiidcd. 3Iol;ir
tooth of rat .5 days o!d. Nnssonov tcclinique.
Pig. 3 Oral epithcliuiii, Golgi a p p w t u s polarizotl in 1);is:il layer :is in iimctive
to right. Mol:tr tooth of r a t 2 days old.
aineloblasts. Stratuiii ~(,ritiiii:~ti~,iiiii
Xassonov technique.
Fig. 4 Mitochondria in c,clls of dcrcloping tooth. Odontohlnsts and dentine
pulp cells above, aineloblasts and cnamcl pnlp cells to Icft. Molar tooth of rat
3 days old. Hegaud technique.
GOLGI APPARATUS I N DEVELOPING T O O T H
33
of the cell (fig. 2). This striking change in tlic form of the
Golgi apparatus might be interpreted to represent an increased activity on the part of the ameloblasts (secretion of
enamel 7) rather than the result of a mechanical displacement
caused by the extreme lengtheiiing of the cells. In any case,
the Golgi apparatus remains constantly polarized o n the side
of the nucleus next to the eriamel (fig. 5 ) in a general position
comparable t o the so-called secretogenous zone of many gland
cells.
In the cytoplasm of the actively secreting ameloblasts there
a r e often found small granules which a r e probably connected
with the formation of enamel. We could not, however, observe that they were formed directly in association with the
Golgi apparatus. Retweeii the nucleus and the end of the
cell adjacent to the enamel pulp is often found a small globular
body which appears brown or black following treatment with
osmic acid. I n ordinary histological preparatioiis this bod)is dissolved, leaving a clear vacuole (fig. 6 ) .
The pulp cells of the criarnel organ which have been derived
from the stratum hlalpighii of the oral cpi thelium underqo
a very striking change from their former stratified condition.
The tissue in the interior of the enamel organ becomes separated and clianged into irregular stellate antistonlosing cells
which resemble in some ways those present in meseiichymal
tissue (figs. 5 and 6). Each of the cells possesses a compact
localized Golgi apparatus (fig. 5) typical of the Golgi allparatus of connective tissue cells. The intermediate layer of
enamel pulp cells, i.e., those subjacent to the ameloblasts, has
retained its more or less flattened stratified epithelial-like
character. The Golgi apparatus of these cells is localized in
the form of a compact network usually at one side of the
nucleus. However, a s in the dental pulp cells, not all a r e
polarized in the same direction. Whether the lack of uniform
polarity of the enamel pulp cells in any one direction is due
t o a change in their position during dedifferentiation from
the oral epitheliuni or to a migration of the Golgi apparatus
within them has not been determined.
34
H. W. BEAMS AX11 R. L. K I K G
The odoiitoblast s which represent the layer of rearranged
cells1 bordering the enamel layer, like the ameloblast s vary
considerably in height (figs. 4, <5,and 6 ) . I n general they
appear wider and not a s tall as the ameloblasts. They possess
a well-formed net-like Golgi apparatus which is verg easily
demonstrated by osmic acid methods (fig. 5). I n fact careful
study of ordinary histological preparations often reveals the
negative image (caiialicular apparatus) of the Golgi apparatus in these cells (fig. 6 ) . It is localized in a position between the nucleus and the discharging end of the cell, a condition so characteristic of gland cells.
Here, as in the ameloblasts, well-defined secretory granules
may be observed which may be associated with the form.a t'ion
of dentine. We have not seen that they a r e formed in the
filaments of the Golgi apparatus. I n the underlying dental
pulp cells the Qolgi apparatus resembles, in a general way,
that which has been described for the enamel pulp cells. It
will be noted that those cells immediately adjacent t o the
odontoblasts a r e arranged into a more or less compact, flattened layer (intermediate layer). These, together with the
deeper cells, which represent typical mesenchymal tissue,
likewise contain it compact net-like Golgi apparatus typical
of connective tissue cells. These cells, while probably individually polarized, a r e not so in any oiie given direction.
However, it is interesting to note that those which have
formed the odoiitoblasts have all become polarized in a common direction (fig. 5).
Alitochoiidria in the ameloblasts, odontoblasts, and pulp
cells do not show any striking characteristics. They a r e in
the form of filariients, short rods, and granules which a r e
fairly numerous and distributed throughout the greater part
of the cytoplasm (fig. 4). However, the mitochondria in both
It may be recalled that tlic odontoblnsts have originated froin mcscnchymal
connective tissue cells which line up in a. single layer, elongate, and become
v n y similar to typical columnar epithelial cells. Such a transformation has been
recently described by 1':rp:inicolaou
( '33) for the guinea pig uterus where
the sloughed off coluinnnr epitlicxliuni is replaced froin the underlying connective
tissue cells. (Am. J o m . Obst. & Gync., vol. 2 5 . )
Fig. 5 Golgi apparatus in cells of developing tooth. Odontoblasts and dentine
pulp cells to right, aineloblasts and enamel pulp cells to left. Molar tooth of
rat 3 days old. Nassonov technique.
Fig. 6 Developing tooth, orientation as in figure 5. Odontoblasts show negative
image of Golgi apparatus. Ameloblasts with small vacuole between nucleus and
underlying pulp cells. Molar tooth of rat 3 days old. Zenker fixation, Tklaficld’s
hematoxylin, eosin.
35
36
H.
w.
REAMS A N D R.
rA. KIKG
the arneloblasts arid odontoblasts seem to show little change
in form i n the region of the Golgi apparatus.
1)il)losomes have beeii found in the active ameloblasts on
the same side of tlie nucleus as the Golgi apparatus. Unfortunately, they have not been observed by us in the outer ameloblasts o r in the oral epithelial cells hut they have been described by Zirnmernian (ISOS) in stratified epithelium a s being
located distal to the nucleus, i.e., where the Golgi apparatus
has been ohserved by us in the oral epithelium.
1) 1SCUSSION
The determination of polarity in cells constitutes one of the
many perplexing problcnis of biology. We can study only its
visible expression which is, in many cases, both structural
and fuiictional, apparently oil the oiie hand as a localized
grouping of cell compoiieiits, on the other as a difference of
fuiictioiial or metabolic activity with respect to the organic
axis of tlie cell.
The l'osition of cytoplwsiiiic components such as the nucleus,
ceiitrosomes, diplosomes, secretion granules, yolk bodies, etc.,
as well a s the position of the cells in relation to their nutrition, has been taken to indicate the structural expression of
the physiological polarity of the cell. However, Lillie ('09)
points out "that polarity is riot a result of the position of the
nucleus or of ally configuration of granules" but is clue t o
some het crogencous physical chemical properties of the
ground substance.
However, more recently the positioii of the Golgi apparatus
has been used as a cytological indicator of the physiological
state and polarity of the cell. Golgi ('OR), D'Agata ('lo),
Basilc ( Y4), Cajal ( 'E),
Cowdry ( 'B),
Rciss ( ' B ) ,CourJasswoin ( '24), Timofcjev ( '%), Ludrier and Rciss ( 'm),
f o r d and ("ramer ( 'as),and Giroud ( '28), hare all described
a reversal in polarity of certain types of cells a s indicated by
the position of the Golgi apparatus. In many of the abovementioned cases the physiological condition of the cells in
which the reversed position of the Golgi apparatus took place
was not knomn. Accordingly, tlicsc rclsult s itre o l m i to question since it has been suggested that the reveiwcl position of
the Golgi a pparatus in the cells may l x due t o it mecliwnical
displacerneiit. But the enamel organ offers, i t S C C ' I ~ I Sto us, a
more conclusive test than most of these c'wses in which a
reversal in polarity has been clcscribecl. It differs in that we
a r e dealing with a casc w2ici.e Ilie kiiown original basal end
of the cell becomes the (liscliai*giiig ciicl a i d reniaiiis sucli
throughout the development of the tooth. It is difficult t o
believe that the reversal ill 1)olwrity of the Golgi ap p arat u s
in this particular case is not associated directly with a change
in the polarity of the cell. I t is t ru e no doubt that as the
cells beginning t o secrete grow ral'idly in height, the Golgi
appar atus is stretched arid extends proportionally, but this
does riot account f o r its migixtioii to the otlicr side of the
nucleus.
Cajal ('14) first clcscribetl the Qolgi apparatus of the
odontoblasts a n d dental pulp cells H S a cornpact localized net.
At about the same time Massenti ('14) described a diffuse
network in nmclohlasts, enamel pulp cells, odontoldast s, and
clental pulp cells. The observations of ,Jasswoin ('24) and of
Timofejev ( 2 5 ) disagree with tlie findings of &lassenti with
whose n7ork they a1)pareiitly were unfamiliar.
Jasswoin and Tiniofejev descrihe a polarized condition for
the anielohlasts and odontoblasts and further note the change
in polarity reemphasized hcre. Scliour ( ' 3 2 ) , in his cliapter
' The Teeth' in ('omdry's Special ('ytologv, suggests tlie necessity for x reexamination of tlie polarity of the anieloblasts.
It may he definitely stated that there is aii obvious iiiorpliological i*evei*salof polarity i i i the ariicloblnsts corres1)onding
t o the cliinige in functional polarity. These facts can hc interprctecl to favor the secretion theory of eiiamcl formsa t'1011.
('ONOLTSION S
1. The Golgi appa ra tus a i d mitochondria of the oral q ) i thelial cells, anieloblasts, enamel 11~11)
cells, otlontoblusts, and
dental pulp cells have been described.
38
H. W. BEAMS A N D It. L. KING
2. The position of the Golgi apparatus has been used as a
criterion of morphological polarity.
3. A change in morphological polarity followiiig a change in
functional polarity has been described for the ameloblasts.
4. This change in morphological polarity iiivolvcs the Golgi
apparatus (and probably the diplosonies) which migrates
around the nucleus to the opposite pole of the cell.
5. Thus tlie Golgi apparatus of active ameloblasts resemble?:
that of glandular cells in that it is located at the active end
of the cell.
6. This may indicate that enamel formation is by secretioii
rather than by transformation of the ameloblasts.
L I T E R A T U R E CITED
13ASII,E,
G. 1914 S u l k niodificazioni dell ’apparato reticolare interno di anininli
refrcctoniizzati. Internat. Montsclir. f . Anat. u. l’liysiol., Bd. 31.
C‘AJAL, S. I<. 1914 Algunas variacioncs fisiol6gicas y patliol6gicas del aparato
rtticul:tr del Golgi. Trab. Ijab. Invest. Biol., vol. 14.
COURRIFK,R. 1922 Contribution B 1’Iiistoplijsiologie du corps tliyroide. Conipt.
rend. Soc. d. Biol., vol. 86.
COUKRIEK,
I<., A N D P. llFiss 1928 Appareil 16ticul6 dc Golgi et polarit6 secr6toire
des cellules paratliyroidiennes. Coiiipt. rend. Soc. d. Biol., vol. 86.
COTID R Y , E. V. 1922 The reticular matcrial as a n indicator of physiologic
reversal in secretory polarity in the thyroid cells of the guinea pig.
Am. .J. Anat., vol. 30.
___
__ 1923 The significance of tlie internal reticukir apparatus of Golgi
i n cellular physiology. Science, vol. 58.
1) ’AGATi, G. 1910 Sulle niodificazioni dell ’apparato reticolare interno nel ’
1 ’epitclio della niucosa gastrica. Bull. SOC.Med. Cliir. Paria., xwl. 2 3 .
Gmoun, A . 1928 i’olarit6 cellulaire ct Appareil de Golgi. Bull. d’IIist. AppI.,
vol. 3.
OOT.GI, C. 1900 Stir line fine particulurit6 de structure de 1’6pithCliuni de In
niuqueuse gastrique ct intestin:ilc de quelqnrs vertChr6s. Arch. Ital.
de Biol., vol. 51.
IIFSNFGIT, L. F. 1926 Sur la situation de I’appareil de Golgi dans les cellules
folliculaircs de l’ovaire de Cobaye. Conipt. rend. Soc. d. Biol., vol. 94.
11 O I K , G.
19% h e r die Histogcnese der ~ e n t i n g r u n d s u b s t a ~ ider
z SSugc
tiere. Arch. f . niikr. Anat. 11. ~ ~ n t ~ z ~ i c k r l n ~ i g s ~ ~ i eBd.
c i ~ a102.
nik.,
1924 On tlie structure and dcvclopiiient of tlie eiuitnel in ~iiani~iials.
Qnart. J. Mic. Sci., vol. 69.
L A M S ,H. 1 9 2 1 Rcclierches sur la structure des partieq constituantes de la
dent cliez les Maniniifi.rcs. Arch. f . Biol., vol. 31.
I,ILLIF,,11. I<. 1909 Pokirity and bilnterahty of the annehd cgg. b:\perirllelits
with centrifugal force. Riol. Bull., rol. 16.
GOLGI APPARATUS I N DEVELOPING T O O T H
39
LUDFORD,
R. J., AND W. CRAMER 1928 The ineclianism of secretion in t h e
thyroid gland. Proc. Royal Soc., B, fol. 104.
I\IANCA, P. 1913 Sulla presenza d i condrioconti nellc cellule degli abbozzi
dentarii. Monit. Zool. Ital., vol. 21. (Cited f r o m Schour.)
MASSENTI, V. 1914 L ’apparato reticolare intenio del Golgi nel gernie dentale.
Monit. Zool. Ital., vol. 2 j .
3fUiIIMERY, J . 11. 1924 The microscopic and general m a t o m y of the tcctli.
Oxford University Press, Oxford.
REISS, P. 1 9 2 L ’appareil de Golgi dans les cellules glandulaires de 1 ’Iiypopliyse.
l’oImit6 fonctionelle et cycle skrktoire. Coinpt. rend. SOC.d. Biol.,
vol. 87.
SEVERINGIIAUS,
A. E. 1933 Cytological observations on the thyroid activated
by anterior pituitary. Anat. Rec., vol. 55.
SCHOUR,
I. 1932 The teeth. Vol. I, Special cytology cdited by E. V. Coivdry.
Hoeber, N. Y.
TINOFEJEV,
8. 192;i Der Anteil des Golgischen Binncnnetzcs a n Iiistogenetisclien
Prozesscn. Arch. Russ. d’Anst., IIist. e t Ernbry., vol. 4.
TURPHINI,
J . 19% De la situation de l’apparcil de Golgi dans quclqaes cellules
glanduleires. Bull. Roc. Med. Riol., vol. 7. (Citcd froin TJiol. Ab$ts.,
vol. 1.)
~ I i I I X E K M A h ” , K. W.
18!)8 B e i t r i g c zur Krnntniss eiiiiyclr 1)riisen und Epitlielien. Arch. f . Mikr. Annt., Bd. 5 2 .
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