Table Of ContentZOOLOGICAL SCIENCE 10: 189-192 (1993) © 1993 Zoological SocietyofJapan
[RAPID COMMUNICATION]
Kinetics of First Spermatogenesis in Young Toads
of Xenopus laevis
TOHRU KOBAYASHI1'2 YOHKO ASAKAWA1 and HlSAAKI IWASAWA1
,
1Biological Institute, Faculty of Science, and 2Graduate School
of Science and Technology, Niigata University,
Niigata 950-21, Japan
—
ABSTRACT The kineticprofile offirst spermatogene- results and the kinetics ofcycling spermatogenesis
sis was examined at22+1°C in young toads ofXenopus in adult toads was discussed.
laevis. The most progressed spermatogenic stage was
primary spermatogonia in newly metamorphosed toads.
Secondary spermatogonia were observed 3 days after MATERIALS AND METHODS
metamorphosis. First leptotene and pachytene sper-
matocytesappeared 17and20daysaftermetamorphosis, Numerous fertilized eggs were obtained from a
respectively. Thenfirstdiplotenespermatocytes, meiotic few pairsofmale andfemale toadsXenopuslaevis
division and round spermatids were observed 42 days, injected with a human chorionic gonadotropin
andfirstmaturespermatozoa70days,aftermetamorpho-
sis. On the basis of these results, the difference (Gonatropin, Teikoku Zoki Co., Tokyo). The
between the time required for first spermatogene- eggs, embryos, and larvae were kept in dechlori-
sis in young toads and cycling spermatogenesis in nated tapwaterat22±1°C. The larvae andyoung
adult toads is discussed. toads were fed on a commercial diet for carp.
These details were previously described [3, 8].
INTRODUCTION Until the timeofthefirstappearance ofsperma-
tozoa after metamorphosis, three to four young
The kinetics of spermatogenesis in amphibians toads were decapitated every day, and the testes
has been studied by several investigators, but the were fixed in Bouin's solution. The testes were
materials used in their studies were mostly sub- then embedded in Paraplast (Sherwood Medical,
adult and adult animals [2, 4, 9, 17]. The St. Louis, U.S.A.), and sectionedserially at4fim.
formation of spermatozoa in juvenile frogs has The sections were stained with Carazzi's hema-
been reported as precocious spermatogenesis in toxylin and eosin.
several species [5, 7, 22, 23], but these papers
simply describe the phenomenon. Recently, we
RESULTS AND DISCUSSION
defined the kinetics of cycling spermatogenesis at
22°C in adult toads of Xenopus laevis [2]. In the In this study, the average body length just after
present study, the time after metamorphosis at metamorphosis was 15 mm, and was 20mm at the
which the most rapidly progressed spermatogenic end ofexperiment (82 days after metamorphosis).
cells appeared at 22°C is examined in young toads As previously reported [8], seminiferous tubules
of this species, and difference between these were clearly observed in young toads just after
metamorphosis. At this time (0 day after meta-
Accepted August 18, 1992 morphosis), the seminiferous tubules were filled
Received June 8, 1992 with primary spermatogonia. The days on which
190 T. KOBAYASHI, Y. ASAKAWA AND H. IWASAWA
Table1. The most rapidly progressed sperma-
togenic stage offirst spermatogenesis in Xenopus
laevis
Days after
metamorphosis Stage
primary spermatogonium
3-16 secondary spermatogonium
17-19 primary spermatocyte
(leptotene)
20-29 zygotene
30-41 pachytene
42-64 diplotene-round spermatid
65-69 elongated spermatid
«•
70-82 spermatozoon
the most rapidly progressed spermatogenic stages
were observed are shown in Table 1. The first
appearance of spermatocytes and spermatids was
observedon17daysand42daysaftermetamorpho-
sis, respectively. Elongated spermatids were seen
65 days after metamorphosis. Seventy days after
metamorphosis, the first spermatozoa were
observed, though the number is a few (Fig. la).
When the roundspermatids differentiatedinto the •« T? $
elongated spermatids (from 45 to 70 days after 0. ^jt %
metamorphosis), pycnotic germ cells were fre-
quently observed (Fig. lb). Fig. 1. First spermatogenesis in X. laevis. a: First
From the results shown in Table 1, the duration spermatozoa (arrow) are seen 70 days after meta-
ofeachspermatogenicprocesswascalculated. The morphosis, b: Pycnoticsubstances(arrowhead)are
frequentlyseenfrom45to70daysaftermetamorpho-
duration of leptotene, zygotene, and pachytene
sis. Scale bar: 30//m.
spermatocytes was 3, 10, and 12 days. The
progression from the diplotene spermatocytes to
theroundspermatidswasaccomplishedwithinone 23 days, adult toads: 4 days). In this study,
day. The duration ofspermiogenesis was 28 days, furthermore, during spermiogenesis the degenera-
whereas the progression of elongated spermatids tion of germ cells, probably round to elongated
to spermatozoa was 5 days. spermatids, was frequently observed. From these
In a previous study, we determined the time facts, it is suggested that the delayofspermiogenic
required for the progression of cycling sperma- progression in first spermatogenesis is caused by
togenesis at 22°C in adult X. laevis ([2], Koba- the failure ofnuclear elongation ofspermatids. It
yashi, unpublished). Although the time required seems, therefore, that the time required for the
for the progression from elongated spermatids to progression from round to elongated spermatids in
spermatozoa was similar between young and adult first spermatogenesis is the real time required for
toads (young toads: 5 days, adult toads: 4 days), the progression from round to elongated sperma-
the present study (Table 1) indicates that the tids plus the time required for the appearance of
progression from round spermatids to elongated round spermatids which could be differentiated
spermatids in young toads was greatly delayed into elongated spermatids. Thus, it is calculated
comparedwiththat inadulttoads [2] (youngtoads: that first appearance of round spermatids which
Kinetics of First Spermatogenesis 191
could be differentiated into elongated spermatids present, the information on these pituitary hor-
is 19 days after the first appearance of round monal levels and gonadal steroid levels in young
spermatids, if the duration of progression from toadsofX. laevis isfew, definedsteroid producing
round to elongated spermatids is similar to that in cells in the testes were not observed electron
adulttoadsasinmice [21]. Todefinethedynamics microscopically 70 days after metamorphosis
in first spermatogenesis, further studies will be (Kobayashi, unpublished). Therefore, it is possi-
necessary. ble that androgen is involved in spermiogenic
In X. laevis and Cynops pyrrhogaster, it is process. In this study, however, whether or not
known that in an in vitro cell culture system the relationship between PRL and androgen pro-
progression from primary spermatocytes to elon- duction duringfirst spermatogenesis is not known.
gated spermatids was accomplished but sper- In conclusion, the present study indicates in X.
miogenesis failed to be completed [1]. When laevis that the duration ofspermatogenesis in first
nuclearelongation proceedsin vivo, inX. laevis, a spermatogenesis in young toads is much longer
few of microtubules contained in spermatids were thanthatofcyclingspermatogenesisinadulttoads.
cast off along with cytoplasm and numerous This delay may be caused by the failure ofnuclear
microtubulesinSertolicellswere situated approxi- elongation of spermatids.
matelyparalleltotheaxisofspermatidselongation
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