Biology Reference
In-Depth Information
A
B
C
D
E
spermatogonia
prim spermatocytes
apoptosis
25
20
1.5
1.0
0.5
0.0
*
*
mlh1
+/+
mlh1
-/-
Fig. 60.
Cross sections of seminiferous tubule in (A)
mlh1
+/+
,
(B)
mlh1
-/-
zebrafi sh, showing
spermatogenic cysts with different types of germ cells, spermatogonia (SPG), primary
spermatocytes (PS), fi rst meiotic division (MI), secondary spermatocytes (SS), second meiotic
division (MII), spermatids (ST), spermatozoa (SPERM), and apoptotic spermatocytes (A). Note
the absence of postmeiosis I stages and the presence of apoptotic spermatocytes with strongly
condensed nuclei in
mlh1
-/-
testis. Inset shows a magnifi ed view of the fi rst meiotic division. In
the wild type, chromosomes are aligned at the cell equator just prior to division. In the mutant,
chromosomes are randomly distributed throughout the nucleus. TUNEL staining of (C)
mlh1
+/+
and (D)
mlh1
-/-
. High numbers of apoptotic spermatocytes are seen in mutant testis. Wild-type
testis shows a very low incidence of apoptosis. (E) Morphometric analysis of testes sections
showing increase in amounts of spermatocytes and apoptoic cells, but not of spermatogonia.
(from Feitsma et al., 2007, with permission by the Genetic Society of America)
Color image of this figure appears in the color plate section at the end of the topic.
Kishi et al. (2008) screened mutagenized zebrafish embryos for
the altered expression of a stress biomarker, senescence-associated
β-galactizidase (
SA-
β
-gal
). For example, the quantitative analysis of
SA-
β
-
gal
, a biomarker of ageing, shows a near linear increase in
SA-
β
-gal
activity
with the age of zebrafi sh (Fig. 62). From a pool of 306 retirovirus-insertional
mutants zebrafi sh, Kishi et al. selected two candidate genes. Of these, one
is known to regulate life span, the
spinster,
and the other
telomeric repeat
binding factor 2
(
terf2
) gene, which plays a role in telomere protection and
telomere length regulation. Both
spinster
and
terf2
mutants are embryonic
lethal but their heterozygous progenies are viable and show an accelerated
appearance of ageing symptoms including accumulation of lipofusion, a
