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Since thyroid-stimulating hormone (TSH) producing cells are thought to play an essential role during metamorphosis, their development was immunohistochemically examined to reveal the appearance and topographical changes in the distribution in the hypophysis of Xenopus laevis tadpole from hatching to the end of metamorphosis. TSH-immunoreactive cells initially appeared at stage 49 (just the beginning of development of the pars nervosa in the hypophysis) as small clusters in the middle part of the pars distalis. They showed conspicuous changes in number during late premetamorphosis: their number reached a peak at stage 51, suddenly decreased at stage 52 (just before completion of the hypophysial histogenesis) followed by gradual increase until the end of metamorphosis. At later stages, they were restricted to the posterior half of the pars distalis.
Table 1. Stage criteria and hypophysial differentiation during
the development of Xenopus laevis
NF-stage Age General survey of development
(days) 1:36' 2.1
37/38 2.2
39 2.4
40 2.8
41 3.2
42 3.3
43 I I 3.6
44 ! 3.8
A 45 '' 4.1
46 I 4.4
47 5.5
48 7.5
49 12
50 15
51 17
52 21
53 54 1 ~
55 32
56 33
57 41
B 58 44
:~
48
Hatching
Existence of hypophysial anlage Beginning of intestinal tract coiling
Appearance of dermal color adaptation Beginning of segregation of primordial
germ cells from dorsal endoderm Appearance of adrenal cortex anlage
Appearance of thyroid anlage Beginning of feeding
Appearance of hindlimb bud Beginning of differentiation in pars
imermedia of adenohypophysis Appearance of forelimb bud
Beginning of development in pars nervosa
Formation of complete gonadal rudiments Beginning of sexual differentiation of
gonads Completion of hypophysial histogenesis First meiotic division in ovary
Appearance of forelimbs Ultimate length of larva First meiotic division in testis
Beginning of head narrowing
---------------------------
!
62 49 Beginning of tail shrinkage
63 51
c 64 53
I 65 54
f 66 58 Completion of metamorphosis
A: Premetamorphosis, B: Prometamorphosis, C: Climax (Terminology
used by Etkin [6])
really useful chart of xenopus stages and developmental landmarks
Figs. 1-4. Sagittal section stained with anti-TSH serum.
Fig. 1. First appearance ofTSH cells with weak immunoreactivity at stage 49 in the middle part of the pars distalis (arrow).
X 230.
Fig. 2. TSH cells with intense immunoreactivity at stage 51. x 230.
Fig. 3. Abrupt decrease in number of TSH cells at stage 52. x 230.
Fig. 4. TSH cells in the posterior half of the pars distalis at stage 66. x 230.
RI: Recessus infundibularis
