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Journal of Mosquito Research, 2013, Vol.3, No.4, 21
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32
ISSN 1927-646X
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29
Figure 11 A Phylogenetic tree for insects used in multiple alignments for transferrin molecule sequence of
Cx.quinquefasciatus
Multiple sequence alignment of the deduced amino acid
sequence of CqTrf with Transferrin amino acid
sequences of five other dipterans,
D. melanogaster
,
A.
aegypti
, and
A. gambiae
,
G. morsitans
,
S. peregrina
and
those of other insects and human is shown (Figure 10).
The deduced molecular phylogeny of insect Trf was
examined using amino acid sequences of Trf from a
number of insect orders including, Diptera, Lepidoptera,
Hymenoptera, Orthoptera, Coleoptera, Dictyoptera and
Isoptera (Figure 11). Within the dipteran transferrins,
Cx.
quinquefasciatus
Trf shows the highest amino acid
identity to
A. aegypti
(85%) and
A. gambiae
(55%),
followed by
D. melanogaster
(54%),
S. peregrina
(52%)
and 34% identity with human transferrin molecule
(NCBI) data base (http://www.ncbi.nlm.nih.gov).
4 Discussion
Our results indicated that, the mosquito,
Cx.
quinquefasciatus
did not support the development of
the entomopathogenic nematode belonging to the
Steinernematid group with its associated bacteria,
Xenorhabdus
. Meanwhile, it could not suppress the
development of the nematode belonging to the
Heterorhabditid group with its associated bacteria,
Photorhabdus
; in this case the nematode succeeded to
complete its life cycle and the bacteria were able to
multiply freely in the host body leading to host death.
Similar results were obtained by (Beerntsen et al.,
1989) who found that the filarioid nematode,
B.
malayi
were susceptible to the immune response of
the mosquito,
Ar. subalbatus
in contrast to
B. pahangi
that developed within the mosquito. A similar
situation was found within
Cx. pipiens
, the mid-gut
environment was toxic to
B. malayi
microfilariae but
not
W. Bancroftiae
microfilariae (Bartholomay et al.,
2003). The filarial parasite interacts in a similar way
to both vertebrate immune response as well as the
mosquito immune response by being either
susceptible or resistant to their immune reponse. The
present work demonstrated that the Steinernematid
nematodes caused an up regulation of transferrin
transcript of the mosquito,
Cx. quinquefasciatus
; In
several mosquito-filarial systems, defensin and
cecropin immune peptides were detected Cecropin
was first characterized and isolated from the
haemolyph of moths (Steiner et al., 1981). When
cecropin was injected into
A. aegypti
mosquitoes, it
suppressed the nematode,
B. pahangi
(Chalk et al.,
1995). Also, up regulation of defensin, gambicin, and
cecropin was demonstrated in
Cx. pipiens
pipiens
upon bacterial inoculation (Bartholomay et al., 2003).
Transferrin is up-regulated in mosquitoes that were
immune to infections. It has been reported from the
haemolymph of
A. aegypti
that melanotically
encapsulated the microfilariae of
Dirofilaria immitis
(Beerntsen and Christensen, 1990) and the
haemolymph of
Ar. subalbatus
melanizing
microfilariae of
B. malayi
(Beerntsen et al., 2000).
Also, transferrin gene was up regulated by wounding,
bacterial or fungal infection and iron overload,
suggesting a functional role in defense and stress
responses (Kim et al., 2008). Insect transferrin has
been reported from various insect species. The
cockroach transferrin resembles vertebrate serum
transferrin in its spectral properties and in having two
iron-binding sites. Transferrin of other insects has
only one iron-binding site in the N-terminal lobe. The
Dipteran transferrins have 45% amino acid identity
with each other but only 27% with human serum
transferrin. The deletion of the C-terminal lobe makes