Program of the 2001 International Worm Meeting - Sternberg Lab ...

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71. Specific functions of linker
histone isoforms in C. elegans
Monika A. Jedrusik 1 , Stefan Vogt 2 ,
Ekkehard Schulze 1
1 Georg-August University of Göttingen, Third
Department of Zoology - Developmental
Biology, Humboldtallee 34A, 37073
Göttingen, Germany
2 Georg-August University of Göttingen,
Institute for X-ray Physics, Geiststraße 11,
37073 Göttingen, Germany
Single gene linker histone knockouts have been
produced in a number of metazoan organisms
ranging from Tetrahymena to mouse. None of
these knockouts produced a significant
phenotype. Therefore it has been proposed that
linker histones could be dispensable for
eukaryotic live. The presence of a linker histone
multigene family, however, is a typical feature
of the genomes of multicellular organisms.
Therefore it may be speculated that although the
linker histone could be dispensable for the live
of individual eukaryotic cells, it may serve
specific and essential functions in the
development of multicellular organisms. We
used RNAi to analyze the complete linker
histone gene family of C. elegans, which
comprises eight genes (H1.1 - H1.6, H1.X, and
H1.Q). Specific and significant phenotypes were
obtained for three of these genes.
Histone H1.1 is essential for the chromatin
silencing in the male and female germ line of C.
elegans. Moreover, the depletion of histone
H1.1 leads to a lack of germ cell proliferation
and differentiation in the hermaphrodite, but not
in the male. This type of hermaphrodite sterility
is similar to the phenotypical appearance of the
mes mutants, which is ascribed to be caused by
a loss of chromatin silencing. No further linker
histone of C. elegans is involved in germ line
development or gametogenesis.
RNA interference with H1.4 expression in
him-8 created adult males with spike tails.
These males were not attracted to
hermaphrodites and did not mate. H1.4 RNAi
resulted also in variable numbers of SPD
neurons in the affected mail tail structures. We
conclude that H1.4 is needed for the completion
of male tail morphogenesis.
The primary structure of H1.X defines a novel
type of linker histone. H1.X is a nuclear as well
as a cytoplasmic protein, and it is prominently
associated with the tonofilaments of the seven
marginal cells of the pharynx. The
tonofilaments are a cytoskeletal structure
created by the intermediate filament system.
H1.X is also expressed in body and vulva
muscles. H1.X RNAi created uncoordinated
animals with an elongated pharynx muscle,
which were occasionally egg laying defective.
We conclude that linker histone isoforms are
very specifically involved in various aspects of
the development of the multicellular organism
C. elegans.
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