196 K. M. Ponnuvel et al.
cognate 71 kDa protein is found upregulated in
the diapausing eggs of B. mori supporting the
earlier data that heat shock protein might play a
cryoprotective role during diapause and also as
molecular chaperones in maintaining the integ-
rity of key metabolic enzymes or structural pro-
teins (Denlinger 2002 ).
Modification of proteins by ubiquitination is
a fundamental mechanism for regulating numer-
ous cellular processes, including DNA repair, cell
cycle regulation, antigen presentation, cell–cell
communication, cell differentiation, and apopto-
sis (Bheda et al. 2009 ). Many biological process-
es rely on targeted protein degradation. Ubiquitin
plays a well-established role in this process, in
which the covalent attachments of polyubiq-
uitin chains to protein substrates culminate in
their degradation via the proteasome. Some of
these so-called “ubiquitin family proteins” have
recently been shown to bind components of the
26S proteasome via their ubiquitin-like domains,
thus implicating proteasome activity in pathways
other than protein degradation (Walters et al.
2004 ). These ubiquitin family proteins might
help in the degradation of proteins which mis-
fold under stress and which can be related to the
upregulation of ubiquitin family proteins in the
non-diapause eggs.
Metabolic Genes
The metabolic rates in insects are typically sup-
pressed during diapause, the metabolic sup-
pression in egg or pupa being very extensive
compared to adult diapause (Danks 1987 ). Two
proteins of metabolic function were identified
in diapausing eggs involved in chitin metabolic
process and chitinase domain containing protein
and one gene encoding chitinase A precursor in
non-diapause eggs. Even though there is no obvi-
ous role for chitin proteins at this stage of embry-
onic development, this protein might have been
obtained from the shell of which it is a major
component. Earlier mRNAs for chitin-binding
proteins that are similar to those in peritrophic
membrane are upregulated in diapause-destined
embryos in Artemia. The mRNAs especially cod-
ing for chitin reactive domains are of embryonic
origin and they might show an unrecognized
contribution to cyst wall assembly by the em-
bryo (Qiu and MacRae 2007 ). However, chitin-
degrading enzymes play a crucial role in post-
embryonic development, especially during larval
molt and pupation. During the molt, proteases
and chitinases are synthesized by epidermal cells
and accumulate in the molting fluid between the
epidermis and the old cuticle (Merzendorfer and
Zimoch 2003 ). The qPCR analysis of chitinase
A precursor showed an upregulation of this gene
during non-diapause suggesting its role in post-
embryonic development in B. mori.
The propanediol utilization (pdu) operon of
Salmonella enterica serovar typhimurium LT2
contains genes needed for the coenzyme B12-
dependent catabolism of 1,2-propanediol (Bobik
et al. 1999 ), but the actual pathway in insects
is not yet known. However, the qPCR analysis
revealed an upregulation of this gene in non-
diapause eggs suggesting a possible role of this
enzyme in the utilization of polyols at the termi-
nation of diapausesRibosomal Genes
In addition to the three ribosomal genes (two in
diapause and one in non-diapause) thought to
have regulatory function, six additional ribosom-
al genes have been identified during diapause
and one gene during non-diapause. Even though
these ribosomal proteins play a role as transla-
tion elongation factors, their role during diapause
is not known. The ribosomal protein L23 found
upregulated by qPCR during non-diapause is
found to play a crucial role in cell proliferation
(Jin et al. 2004 ).Transposable Elements
One gene, with negative regulation of tran-
scription, was identified to have a transposable
elemental role. Transcriptional repression is re-
quired for the establishment of the temporally
and spatially complex patterns of gene expres-