5.7.3 Vitellogenins and Yolk Proteins of Crustaceans and Other Invertebrates
201
Unexpectedly, the VG of the cockroach Nauphoeta cinerea is a homodimer of 244-kDa polypeptides [115].
The VGs of group 2 are monomers or dimers
of 170- to 190-kDa subunits, the precursors of
which are already of approximately equal size in
the fat body. To this group belong the Hymenoptera and the primitive dipterans, the Nematocera
(mosquitoes). One can imagine that in the evolution of this group the VG genes lost the exons for
the L-polypeptide [269]. Deviating somewhat
from this picture is the 65-kDa subunit, arising
from the same precursor, which was recently
found in addition to the 200-kDa subunit in the
VG of the mosquito Aedes aegypti [61].
Group 3 includes only the higher dipterans,
the Brachycera (flies). The native VGs are of
about 200 kDa and are made up of polypeptides
of about 50 kDa corresponding to the primary
translation products. In this case, evolution of the
VG genes resulted in the loss of the exons for the
H subunit. The VGs of about ten species of flies
have been investigated in detail [21, 22, 41, 96,
135, 144, 209]. One peculiarity of this group is
that in addition to the continuous synthesis ofVG
in the fat body there is also stage-specific synthesis in the ovary, probably in the follicle epithelial
cells [22, 282]. This is possibly related in some
way to the already-mentioned characteristic hormonal control of VG synthesis. According to
experiments with Drosophila cell cultures, juvenile hormone affects only synthesis in the ovary,
and 20-hydroxyecdysone only synthesis in the fat
body [166]. In the fly Stomoxys calcitrans, no
female-specific proteins are ever found in the
haemolymph or yolk proteins in the fat body; VG
synthesis is restricted to the ovary [41, 109].
Minor VG synthesis has also been observed in
isolated ovaries of the potato beetle Leptinotsara
decemlineata [199].
Most insects contain multiple VGs and VTs
that are recognizable by their varying molecular
size, for example in the cockroach Leucophaea
maderae [31], or by differences in immunological
or electrophoretic properties. This is probably a
case of products of non-allelic loci. Locusta migratoria has two VG genes, most dipterans have
three, and Aedes aegypti has four [29, 35,
84, 121]. There are three VG polypeptides in
Drosophila which agree in 43 % of their 420-442
amino acids, and are encoded by three homologous genes on the X chromosome. Of these, YP-1
and YP-2 contain only one intron and are separated by 1.2 kb; YP-3 lies about 1000 kb away and
has two introns. The three genes are undoubtedly
the result of a double duplication [83]. The genes
are expressed in a sex-, tissue- and stage-specific
manner, and the recently isolated yolk-specific
factor I (YPF1), which binds to a specific site on
the YP-1 gene, is probably involved in this regulation [167].
Proteins originating in the VGs account for
60-90 % of the total soluble egg protein; other
plasma proteins are found in minor amounts in
the egg [109]. Amongst these subsidiary components of the yolk proteins are, for example, the
microvitellin of Manduca sexta and the paravitellin of Hyalophora cecropia. Microvitellin is a protein of 26 kDa without carbohydrate, lipid or
phosphate and which is produced in the fat body
17 days before hatching of the adult animal; it is
transported to the ovary by the haemolymph and
taken up unchanged into the oocytes. The
sequence of 232 amino acids derived from the
cDNA has no similarity to any other known protein [265]. In the eggs of Bombyx mori, 40 % of
the yolk protein consists of vitellin, 35 % of the
group of 30-kDa proteins [174] and 25 % of the
egg-specific protein (ESP). Mature ESP is a glycophosphoprotein of 225 kDa consisting of two
subunits of 72 kDa and one of 64 kDa. The
two types of subunit arise by different posttranslational processing from a primary translation product of 558 amino acids [116, 222]. Only
after the onset of embryogenesis is a trypsin-like
proteinase of 30.5 kDa produced which cleaves
certain bonds in the ESP in a highly specific way
[117]. It has been shown in Manduca that lipophorin is also taken up into the egg from the haemolymph [126, 134]. In many cockroaches, locusts,
beetles and butterflies, the females reabsorb a
part of the spermatophore material before the
remaining spermatophore is ejected. The males
of Melanoplus sanguinipes pass on an average
of seven spermatophores during copulation,
although one alone contains more than enough
sperm; it could be shown immunologically that
male proteins find their way unchanged into the
oocytes [78].
5.7.3 Vitellogenins and Yolk Proteins
of Crustaceans and Other Invertebrates
The egg yolk of crustaceans contains one or more
lipoproteins (lipovitellins) of 310-600 kDa. The
lipovitellin of the small brine shrimp Artemia
salina is a lipoglycoprotein of 600 kDa with polypeptides of 190 and 68 kDa, 3.3 % carbohydrate
and 8.6 % lipid; it is coloured by the presence of
201
Unexpectedly, the VG of the cockroach Nauphoeta cinerea is a homodimer of 244-kDa polypeptides [115].
The VGs of group 2 are monomers or dimers
of 170- to 190-kDa subunits, the precursors of
which are already of approximately equal size in
the fat body. To this group belong the Hymenoptera and the primitive dipterans, the Nematocera
(mosquitoes). One can imagine that in the evolution of this group the VG genes lost the exons for
the L-polypeptide [269]. Deviating somewhat
from this picture is the 65-kDa subunit, arising
from the same precursor, which was recently
found in addition to the 200-kDa subunit in the
VG of the mosquito Aedes aegypti [61].
Group 3 includes only the higher dipterans,
the Brachycera (flies). The native VGs are of
about 200 kDa and are made up of polypeptides
of about 50 kDa corresponding to the primary
translation products. In this case, evolution of the
VG genes resulted in the loss of the exons for the
H subunit. The VGs of about ten species of flies
have been investigated in detail [21, 22, 41, 96,
135, 144, 209]. One peculiarity of this group is
that in addition to the continuous synthesis ofVG
in the fat body there is also stage-specific synthesis in the ovary, probably in the follicle epithelial
cells [22, 282]. This is possibly related in some
way to the already-mentioned characteristic hormonal control of VG synthesis. According to
experiments with Drosophila cell cultures, juvenile hormone affects only synthesis in the ovary,
and 20-hydroxyecdysone only synthesis in the fat
body [166]. In the fly Stomoxys calcitrans, no
female-specific proteins are ever found in the
haemolymph or yolk proteins in the fat body; VG
synthesis is restricted to the ovary [41, 109].
Minor VG synthesis has also been observed in
isolated ovaries of the potato beetle Leptinotsara
decemlineata [199].
Most insects contain multiple VGs and VTs
that are recognizable by their varying molecular
size, for example in the cockroach Leucophaea
maderae [31], or by differences in immunological
or electrophoretic properties. This is probably a
case of products of non-allelic loci. Locusta migratoria has two VG genes, most dipterans have
three, and Aedes aegypti has four [29, 35,
84, 121]. There are three VG polypeptides in
Drosophila which agree in 43 % of their 420-442
amino acids, and are encoded by three homologous genes on the X chromosome. Of these, YP-1
and YP-2 contain only one intron and are separated by 1.2 kb; YP-3 lies about 1000 kb away and
has two introns. The three genes are undoubtedly
the result of a double duplication [83]. The genes
are expressed in a sex-, tissue- and stage-specific
manner, and the recently isolated yolk-specific
factor I (YPF1), which binds to a specific site on
the YP-1 gene, is probably involved in this regulation [167].
Proteins originating in the VGs account for
60-90 % of the total soluble egg protein; other
plasma proteins are found in minor amounts in
the egg [109]. Amongst these subsidiary components of the yolk proteins are, for example, the
microvitellin of Manduca sexta and the paravitellin of Hyalophora cecropia. Microvitellin is a protein of 26 kDa without carbohydrate, lipid or
phosphate and which is produced in the fat body
17 days before hatching of the adult animal; it is
transported to the ovary by the haemolymph and
taken up unchanged into the oocytes. The
sequence of 232 amino acids derived from the
cDNA has no similarity to any other known protein [265]. In the eggs of Bombyx mori, 40 % of
the yolk protein consists of vitellin, 35 % of the
group of 30-kDa proteins [174] and 25 % of the
egg-specific protein (ESP). Mature ESP is a glycophosphoprotein of 225 kDa consisting of two
subunits of 72 kDa and one of 64 kDa. The
two types of subunit arise by different posttranslational processing from a primary translation product of 558 amino acids [116, 222]. Only
after the onset of embryogenesis is a trypsin-like
proteinase of 30.5 kDa produced which cleaves
certain bonds in the ESP in a highly specific way
[117]. It has been shown in Manduca that lipophorin is also taken up into the egg from the haemolymph [126, 134]. In many cockroaches, locusts,
beetles and butterflies, the females reabsorb a
part of the spermatophore material before the
remaining spermatophore is ejected. The males
of Melanoplus sanguinipes pass on an average
of seven spermatophores during copulation,
although one alone contains more than enough
sperm; it could be shown immunologically that
male proteins find their way unchanged into the
oocytes [78].
5.7.3 Vitellogenins and Yolk Proteins
of Crustaceans and Other Invertebrates
The egg yolk of crustaceans contains one or more
lipoproteins (lipovitellins) of 310-600 kDa. The
lipovitellin of the small brine shrimp Artemia
salina is a lipoglycoprotein of 600 kDa with polypeptides of 190 and 68 kDa, 3.3 % carbohydrate
and 8.6 % lipid; it is coloured by the presence of