Strongylocentrotus purpuratus Genes in Development: Tektin
Tektin A1 is one of three integral filamentous protein components
of outer doublet microtubules. It is synthesized in sea urchins
in an amount correlating to the length of embryonic cilia.
The presence of low levels of tektin mRNAs at stages of
development prior to ciliogenesis may indicate that the tektins
are also involved in other cellular processes such as centriole replication,
mitosis and cell division (Norrander et al., 1995).
Tektin A1 is a ~ 53 KDa protein.
The tektin A and B polypeptide chains each consist of several
alpha-helical coiled-coil regions connected by spans
of non-helical linkers (Chen et al., 1993).
Nothern blotting showed that low levels of tektin mRNA were detected in the
unfertilized egg, and there were no changes in message size observed
throughout development. Ciliogenesis in this species begins at about
8 hours, after which point there was a marked rise in the level
of each tektin mRNA.
Post- fertilization levels of tektin A1 mRNA
were lower than those of tektin B1 and tektin C1 mRNAs. With respect to peak levels, tektin A1 mRNA increased >20-fold
over post-fertilization levels. Before ciliogenesis, the level
of tektin A1 mRNA was low and relatively constant. The message level
fell rapidly after hatching, however the postciliogenesis level were
somewhat higher than those seen in the early cleavage stages (Norrander et al., 1995).
Tektins form filamentous polymers in the walls of ciliary and flagellar
microtubules. The organization of tektins in microtubules is not known in
detail, but tektins probably interact directly with tubulin.
Immunofluorescence microscopy has demonstrated that tektins A1, B1 and C1 are present in all nine flagellar doublet microtubules and possibly in the central pair microtubules (Steffen and Linck, 1988).
Temporal accumulation *
Method: Nothern blot analysis
Reference: Norrander et al., 1995
12.5 hours (blastula)
16 h 50 min (rotating blastula)
18.75 hours (hatched, swimming blastula)
24 h 50 min (mid-gastrula)
* The autoradiograms were quantitated densitometrically,
normalizing mRNA band with corresponding ubiquitin signal.
Action of animalizing agents
To determine if tektin mRNA levels were increased in embryos
deploying cilia of increased ciliary length, normal embryos were compared with
At the period of ciliogenesis, when the tektin mRNA reached a peak,
the levels of tektin A1 mRNA were measured in normal and animalized embryos.
During this period, ciliary elongation was essentially linear and the level of tektin A1 mRNA remained relatively constant.
In the case of zinc-treated embryos, tektin A1 mRNA increased only by about 1/3 (the levels
of tektin B, tektin C, ubiquitin and tubulin messages increased more than 2-fold).
This average increase in tektin A1 message alone correlates with the 1/3 ciliary
length increase seen after the minimal animalization that is characteristic of this
species (Norrander et al., 1995).