CN106011172A - Preparation method of bombyx mori capable of synthesizing and secreting hydrophilic sericin on posterior division of silkgland - Google Patents

Abstract

The invention provides a preparation method of silkworm whose posterior silk gland can synthesize and secrete hydrophilic sericin. The method comprises the following steps: recombining the DNA molecule encoding the amino acid sequence SER into the silkworm chromosome, and screening the silkworms capable of synthesizing and secreting hydrophilic sericin in the rear silk glands by using fluorescent protein markers. Wherein, the nucleotide sequence from the 5' end to the 3' end of the DNA molecule encoding the amino acid sequence SER is the Bombyx mori fibroin heavy chain protein Fib-H gene promoter, the Bombyx mori Fib-H gene 5' end signal peptide coding sequence, Silk gum protein SER3 coding sequence Ser3 and silkworm Fib-H gene 3' end sequence. The method of the present invention can enable the hydrophilic sericin gene specifically expressed in the middle silk gland of the silkworm to be efficiently expressed and secreted in the rear silk gland at the same time, and after the silkworm mature larva spins and cocoons, the silk fiber containing the hydrophilic sericin gene can be obtained. Silkworm cocoons with water-based sericin components, and then obtain silkworm silk with improved fiber water absorption performance.

Description

Preparation method of silkworm whose posterior silk gland can synthesize and secrete hydrophilic sericin

technical field

The invention relates to the field of bioengineering, in particular to a method for preparing silkworms whose posterior silk glands can synthesize and secrete hydrophilic sericin.

Background technique

The silkworm spins silk to make cocoons, and the cocoon silk can produce silk protein fibers. Silk glands are highly specialized organs for synthesizing and secreting silk proteins in silkworms. A silkworm larva has two very similar silk glands, and each silk gland is divided into three functional areas: anterior silk gland, middle silk gland and posterior silk gland . The middle silk gland and the posterior silk gland are the synthesis and secretion sites of silk protein, while the anterior silk gland is the channel through which silk protein is exported out of the body.

The rear silk gland of the silkworm mainly synthesizes and secretes silk fibroin, a tough and elastic protein with a β-fold crystal structure, which accounts for 70-80% of the total cocoon silk, and is the basic raw material for making silk and other textiles. Silk fibroin protein includes silk fibroin light chain (light chain, Fib-L) and heavy chain (heavy chain, Fib-H), and P25 protein (also known as fiber hexamerin, fibrohexamerin, Fhx/P25) etc. (Yamaguchi et al. al., 1989; Sprague 1975; Couble et al., 1983). They are respectively encoded by the silk fibroin genes fib-H, fib-L and p253, and their expression has strict tissue and developmental stage specificity (Couble et al., 1983; Maekawa & Suzuki 1980; Tsujimoto et al., 1981; Tsuda et al. al., 1981). In the posterior silk gland of Bombyx mori, Fib-H, Fib-L and P25 form a complex with a molar ratio of 6:6:1 as the basic structural unit of silk fibroin (Inoue 2000), where Fib-H and Fib-L They are connected to each other by disulfide bonds, and P25 binds to the Fib-H/Fib-L complex by non-covalent bond-hydrophobic interaction. P25 has a chaperone-like function and plays an important role in the folding of the silk fibroin complex and the secretion of insoluble long-chain proteins (Tanaka et al., 1999).

The middle silk gland cells of the silkworm contain more than seven major sericin proteins, which are mainly encoded by three Ser1, Ser2 and Ser3 genes located in the 11th linkage group of the silkworm (Okamoto et al., 1982; Michaille et al., 1986; 1990; Takasu et al., 2007), their expression is controlled by tissue location and developmental stage. Ser1 gene transcribes 4 kinds of sericin mRNAs of different lengths only in 150 cells in the posterior part of the middle silk gland, and one 2.8kb mRNA is only in 42 cells near the posterior silk gland throughout the 5th instar larval stage expression, while 10.5, 9.0 and 4.0kb three mRNAs were only produced in the remaining 108 cells through different splicing pathways at different developmental stages (Couble et al., 1983). Alternative splicing of exons encoding Ser1 mRNA produces multiple protein variants at different developmental stages of larvae, resulting in a single gene producing proteins with different structures and properties after each transcription event in the same body. The primary transcription of Ser1 Different splicing of proteins is also regulated by developmental stage (Couble et al., 1983; Garelet al., 1997). At the beginning of the 5th instar, the Ser2 gene is expressed in all the middle silk gland cells, and later its expression is restricted to the anterior part of the middle silk gland (Takasu et al., 2010); Ser3 is only expressed in the middle and front part of the middle silk gland protein (Takasu et al., 2010).

The silk fibroin protein synthesized by the posterior silk gland cells of Bombyx mori is continuously secreted into the lumen of the silk gland, and gradually moves from the lumen of the posterior silk gland to the lumen of the middle silk gland. During the process of spinning and cocooning of silkworm larvae after maturation, silk fibroin protein molecules continuously aggregate into fibrils (also called fibrils) with a diameter of about 0.1 μm and irregular circular cross-sections, and further tightly aggregated to form silk fibroin. "core". The fibrils are composed of crystalline fibers and non-crystalline fiber molecular aggregates alternately connected in series along the uranium direction. The fibrils are closely connected to each other, firmly connected through the peripheral molecular side chains, and have no interstitial filling. This is the special luster and ability of silk fibres. Molecular basis for the production of ultrafine protein fibers.

The silk fibrils in the silk gland of the silkworm are wrapped with four layers of sericin during the process of forming silk fibers and moving to the front, among which the SER3 protein is wrapped in the outermost layer because it is synthesized in the front of the middle silk gland Layer, not in direct contact with silk fibroin fibers. SER3 protein has low crystallinity and high fluidity. Sericin accounts for 20%-30% of silk, and its molecular conformation is mainly random coils, with a small amount of β structure, but no α helical structure, and its molecular space structure is loose and disordered.

The amino acid composition of sericin protein and silk fibroin protein secreted by silkworm silk gland has very obvious difference in amino acid preference. Silk fibroin is mainly composed of glycine, alanine, serine and tyrosine. Sericin is mainly composed of serine, aspartic acid, threonine, glycine and glutamic acid. The contents of glycine, alanine and tyrosine in sericin were significantly lower than that of silk fibroin, and the content of free amino acids was significantly higher than that of silk fibroin. There are many long side chain amino acids such as arginine, lysine, glutamic acid, methionine, tryptophan and tyrosine on the sericin chain, and the surface of the polypeptide chain also contains -OH, -COOH, -NH ₂ and other polar hydrophilic groups. Therefore, sericin has excellent functions of moisture absorption, moisturizing and odor absorption, among which the water absorption and fluidity of sericin SER3 are significantly higher than the four inner sericin proteins translated by Ser1 gene that are close to silk fibroin.

During the reeling and scouring operations of silkworm silk textile production, the sericin on the surface of the silk is almost completely removed, and SER3, which is the main component of the outer sericin, is more thoroughly removed. Silkworm silk fabrics that retain sericin not only have the problems of poor gloss and uneven dyeing, but also have poor fabric softness and poor wearing comfort. Therefore, degumming is a technological requirement to improve silk luster and ensure dyeing uniformity. Although the water absorption of the silk fiber molecules composed of silk fibroin after degumming is still nearly 30% higher than that of cotton fibers, the feeling of wearing silk is not as absorbent as cotton cloth. This is due to the high price of silk, which is almost all thin fabrics, and the total water absorption of the fibers is small. Therefore, adding sericin protein into silk fibroin protein is expected to change the fiber structure and physical and chemical properties of silk fibroin, and realize the purpose of changing fiber function, especially the dual characteristics of silk fibroin and sericin are used at the same time. Sericin remains on the fiber surface, or a functional utilization that cannot be achieved by sericin coating on the surface of silk fibers or fabrics.

Contents of the invention

In order to solve the above-mentioned technical problems, the present invention provides a method for preparing silkworms whose posterior silk glands can synthesize and secrete hydrophilic sericin, and the silkworms obtained by the method can obtain silk fibers after the mature larvae spin and cocoon Silkworm cocoons containing hydrophilic sericin components.

To achieve the above object, the present invention adopts the following technical solutions:

In one aspect, the present invention provides a method for preparing silkworms whose posterior silk glands can synthesize and secrete hydrophilic sericin, comprising the following steps:

Recombining the DNA molecule encoding the amino acid sequence SER into the silkworm chromosome, expressing, translating and screening to obtain the silkworm silkworm in which the posterior silk gland can synthesize and secrete hydrophilic sericin;

Wherein, the nucleotide sequence from the 5' end to the 3' end of the DNA molecule encoding the amino acid sequence SER is the Bombyx mori silk fibroin heavy chain protein Fib-H gene promoter, the Bombyx mori Fib-H gene 5' end signal peptide coding sequence , silkworm sericin protein SER3 coding sequence Ser3 and silkworm Fib-H gene 3' end sequence.

In a specific embodiment, silkworm sericin protein SER3 has the amino acid sequence shown in SEQ ID NO:1.

Preferably, the DNA molecule encoding the amino acid sequence shown in SEQ ID NO:1 has the nucleotide sequence shown in SEQ ID NO:2.

In another specific embodiment, the amino acid sequence SER has the amino acid sequence shown in SEQ ID NO:3.

Preferably, the DNA molecule encoding the amino acid sequence shown in SEQ ID NO:3 has the nucleotide sequence shown in SEQ ID NO:4.

In a specific embodiment, recombining the DNA molecule encoding the amino acid sequence SER onto the silkworm chromosome specifically includes the following steps:

Constructing a transposable vector comprising a DNA molecule encoding the amino acid sequence SER; and introducing the transposable vector into silkworm eggs of Bombyx mori.

Preferably, the method for introducing the transposable vector into silkworm eggs is microinjection.

Preferably, the transposable vector is a recombinant gene Ser3 transposable vector PB-ser constructed from a piggyBac transposon.

More preferably, the piggyBac transposon construction recombinant gene Ser3 transposable vector PB-ser specifically includes the following steps:

Connect the silkworm Fib-H gene promoter and the silkworm Fib-H gene 5' signal peptide coding sequence at the upstream 5' end of the SER3 protein coding nucleic acid sequence, and connect the silkworm Fib-H gene at the downstream 3' end of the SER3 protein coding nucleic acid sequence The 3' end sequence of the recombinant gene Ser was obtained; the PiggyBac-3xP3-DsRed plasmid (sequence shown in SEQ ID NO: 6) with eye and nerve-specific promoter SV40 and red fluorescent protein DsRed element was combined with artificially synthesized The Ser sequence was double-digested with AscI and FseI respectively; the digested piggybac-3xP3-DsRed plasmid was ligated with the Ser sequence to obtain the transposition vector PB-Ser.

Preferably, the transposable vector PB-Ser has the nucleotide sequence shown in SEQ ID NO:5.

In another aspect, the present invention provides a transposable vector having a DNA molecule encoding the amino acid sequence shown in SEQ ID NO:3.

Preferably, the transposable vector is a recombinant gene Ser3 transposable vector PB-ser constructed from a piggyBac transposon.

Preferably, the transposable vector has the nucleotide sequence shown in SEQ ID NO:5.

By means of the above technical solution, compared with the prior art, the present invention has the following advantages: the present invention provides a method for preparing silkworms whose posterior silk glands can synthesize and secrete hydrophilic sericin, and the method can make silkworms The hydrophilic sericin protein SER3 specifically expressed in the middle silk gland can be highly expressed and secreted in the posterior silk gland at the same time, and after the silkworm mature larva spins and cocoons, the silk fiber containing the hydrophilic sericin component can be obtained. silkworm cocoons, and then obtain silkworm silk and silk fabrics with improved fiber water absorption properties.

Description of drawings

Fig. 1 illustrates the recombinant gene Ser sequence encoding the amino acid sequence of SER;

Figure 2 illustrates the transposable vector PB-Ser of the recombinant gene Ser;

Fig. 3 shows the difference between recombinant gene Ser mutant silkworm and wild type silkworm.

detailed description

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings. It should be understood that the following examples are only used to illustrate the present invention, and should not be construed as limiting the scope of the present invention.

The invention provides a preparation method of silkworm whose rear silk gland can synthesize and secrete hydrophilic sericin protein. The DNA molecule encoding the amino acid sequence SER is recombined into the silkworm chromosome, and then obtained through expression and translation. Wherein, the nucleotide sequence from the 5' end to the 3' end of the DNA molecule encoding the amino acid sequence SER is the Bombyx mori fibroin heavy chain protein Fib-H gene promoter, the Bombyx mori Fib-H gene 5' end signal peptide coding sequence, the Silk gum protein SER3 coding sequence Ser3 and silkworm Fib-H gene 3' end sequence.

In the preparation method of the present invention, the coding amino acid sequence SER is a recombinant expression sequence of the sericin protein sequence SER3 that can be highly expressed in the posterior silk gland of the silkworm and specifically expressed in the middle silk gland of the silkworm. The DNA molecule encoding the amino acid sequence SER is recombined into the silkworm chromosome, and after the encoding amino acid sequence SER is expressed in the silkworm body, the sericin protein SER3 can be synthesized at the same time as the silk fibroin protein in the silk gland cells of the silkworm larvae. Furthermore, the sericin protein SER3 synthesized by the posterior silk gland cells can be secreted into the gland cavity, and coexists among the silk fibroin protein molecules in the gland cavity of the posterior silk gland. Further, along with the silk fibroin in the lumen of the posterior silk gland, it gradually moved to the lumen of the middle silk gland. Further, in the process of silk spinning and cocooning after the silkworm larva matures, the fibrils of silk fibroin protein molecules are formed and filled between the fibrils, so that sericin fillers appear between the silk fibrils without interstitial filling. During the silk spinning process of silkworm larvae, some SER3 overflowed from the silk fibrils and was wrapped between the inner sericin and silk fibroin, accompanied by the restriction of the front silk gland duct and the extrusion of the spinning hole.

In a specific embodiment, the silkworm sericin protein SER3 has the amino acid sequence shown in SEQ ID NO:1. The DNA molecule encoding the amino acid sequence shown in SEQ ID NO:1 has the nucleotide sequence shown in SEQ ID NO:2.

In a specific embodiment, the amino acid sequence SER has the amino acid sequence shown in SEQ ID NO:3.

Due to the degeneracy of codons, there may be many kinds of DNA molecules that can encode the amino acid sequence SER of the present invention.

In a specific embodiment, the DNA molecule encoding the amino acid sequence shown in SEQ ID NO:3 has the nucleotide sequence shown in SEQ ID NO:4.

Those skilled in the art can recombine the DNA molecule encoding the amino acid sequence SER into the silkworm chromosome according to the general silkworm transgenic operation and the steps of obtaining transgenic silkworm, and prepare a stable genetic rear silk gland that efficiently synthesizes and secretes hydrophilic sericin silkworm model.

In a specific embodiment, recombining the DNA molecule encoding the amino acid sequence SER into the silkworm chromosome comprises the following steps: constructing a transposable vector comprising the DNA molecule encoding the amino acid sequence SER; and introducing the transposable vector into silkworm eggs.

In yet another specific embodiment, the following steps are taken to integrate the DNA molecule encoding the amino acid sequence SER into the silkworm chromosome:

1. Construction of transposable vectors

Connect the silkworm Fib-H gene promoter and the silkworm Fib-H gene 5' signal peptide coding sequence at the upstream 5' end of the SER3 protein coding nucleic acid sequence, and connect the silkworm Fib-H gene at the downstream 3' end of the SER3 protein coding nucleic acid sequence The 3' end sequence of the recombinant gene Ser was obtained. The piggyBac-3xP3-DsRed plasmid (sequence shown in SEQ ID NO: 6) with the eye and nerve-specific promoter SV40 and the red fluorescent protein DsRed element and the artificially synthesized Ser sequence were subjected to AscI and FseI double enzyme digestion . The digested piggybac-3xP3-DsRed plasmid and the Ser sequence were connected to form the transposable vector PB-Ser. The structural diagrams of the recombinant gene Ser and the transposable vector PB-Ser are shown in Figure 1 and Figure 2 .

2. Obtaining transgenic silkworms

(1) In a sterile and non-nucleic acid-polluted environment, inject 4000ng-5000ng of the transposable carrier plasmid into each silkworm egg by microinjection;

(2) The silkworm eggs after injection are sealed with non-toxic materials to coat the injection hole, and then in a sterile environment, protect the silkworm eggs with 26°C-27°C, 75%-80% relative humidity, and natural light until they hatch, and the larvae continue to hatch after hatching. Feed with mulberry leaves or artificial feed in the same temperature, humidity and light environment. After cocooning, the larvae continue to be protected with the same temperature, humidity and light environment until the adults emerge;

(3) After selfing or backcrossing of silk moths after emergence, the hatched larvae are fed with mulberry leaves or artificial feed, and the larvae at the 3rd to 5th instar, pupal stage or adult stage are investigated under a fluorescent microscope, and the eyes show red fluorescence Individuals, as transgenic G1 generation individuals;

(4) Select transgenic G1 generation individual embryos, larvae, pupae or adults with red fluorescent eyes for subculture, and obtain stable genetic posterior silk glands that efficiently synthesize and secrete hydrophilic sericin after G6 generation silkworm.

The present invention also provides a method for identifying the transgenic silkworm whose posterior silk gland efficiently synthesizes and secretes hydrophilic sericin after the G1 generation. Observed under a fluorescent microscope, the larvae whose silk cocoons are green fluorescent are: Ser3-transgenic silkworm silkworm with high-efficiency synthesis and secretion of hydrophilic sericin in the posterior silk gland.

The present invention also provides a transposable vector having a DNA molecule encoding the amino acid sequence shown in SEQ ID NO:3.

In some embodiments, the transposable vector is PB-Ser, comprising piggyBac transposase recognition sequences piggyBac 3'LTR and piggyBac 5'LTR, ocular and neural specific promoter 3xP3, EGFP reporter gene, polyadenylation of SV40 Acid-tailed sequence, recombinant gene Ser. The piggyBac transposase recognition sequence is respectively located at the TTAA site on the left end of piggyBac 3'LTR and the right end of piggyBac 5'LTR on the transposable carrier; It is artificial promoter 3×P3, EGFP reporter gene, polyadenylation tailing sequence of SV40 and recombinant gene Ser.

In some preferred embodiments, the transposable vector has a nucleotide sequence as shown in SEQ ID NO:5.

The present invention also provides the silkworm silkworm in which the posterior silk gland of stable inheritance prepared by the method of the present invention efficiently synthesizes and secretes hydrophilic sericin SER3.

The silkworm whose posterior silk gland efficiently synthesizes and secretes hydrophilic sericin protein provided by the present invention can detect hydrophilic sericin protein in the posterior silk gland cells of the 5th instar larval stage and secrete protein in the posterior silk gland cavity SER3 ingredients. In some preferred embodiments, the content of sericin protein SER3 in the secreted silk protein accumulated in the cavity of the posterior silk gland of mature larvae is greater than 5%, and the content of sericin protein SER3 in the extruded silk protein is greater than 10%.

In order to further understand the present invention, the method provided by the present invention will be described in detail below in conjunction with the examples.

Example 1

Preparation of transposable vector for recombinant gene Ser

The promoter of the silkworm Fib-H gene and the 5' terminal signal peptide coding sequence were connected upstream of the sericin protein SER3 coding nucleotide sequence Ser3, and the 3' terminal sequence of the silkworm Fib-H gene was connected downstream to obtain the recombinant gene Ser. The nucleotide sequence is shown in SEQ ID NO:4.

The piggyBac-3×P3-DsRed plasmid (sequence shown in SEQ ID NO: 6) containing the artificial promoter 3×P3 composed of three concatenated Bombyx mori eye and nervous system-specific transcription factor PAX-6 binding sequences was combined with artificial The synthesized Ser sequences were subjected to double digestion with AscI and FseI, respectively. The digested piggyBac-3×P3-DsRed plasmid and Ser sequence were reacted overnight at 16°C with T4 ligase. Then the product was detected by electrophoresis, and the digested Ser band was purified, recovered and sequenced. The correct sequence identified is the transposable carrier PB-Ser, and its nucleotide sequence is shown in SEQ ID NO:5.

The specific schematic diagram is shown in Figure 1-Figure 2. Figure 1 shows the recombinant gene Ser, and Figure 2 shows the transposable vector of the recombinant gene Ser.

Example 2

Preparation of Bombyx mori with posterior silk glands capable of synthesizing and secreting hydrophilic sericin

According to the common silkworm transgenic operation and transgenic silkworm obtaining steps, the recombinant gene Ser sequence is integrated into the genome of the silkworm N4 variety, and the specific steps for obtaining the Ser silkworm are as follows:

(1) In a sterile and non-nucleic acid-polluted environment, inject 4000ng-5000ng of the transposable carrier plasmid into each silkworm egg by microinjection;

(2) The silkworm eggs after injection are sealed with non-toxic materials to coat the injection hole, and then in a sterile environment, protect the silkworm eggs with 26°C-27°C, 75%-80% relative humidity, and natural light until they hatch, and the larvae continue to hatch after hatching. Feed with mulberry leaves or artificial feed in the same temperature, humidity and light environment. After cocooning, the larvae continue to be protected with the same temperature, humidity and light environment until the adults emerge;

(3) After selfing or backcrossing of silkworm moths after eclosion, the hatched larvae of the laid eggs are raised with mulberry leaves or artificial feed, investigated under a fluorescent microscope at the pupal stage, and the individuals whose eyes show red fluorescence are transgenic G1 generation individuals;

(4) Individuals with red fluorescent eyes in the pupae of transgenic G1 individuals were selected to be subcultured, and silkworms with stable genetic posterior silk glands efficiently synthesizing and secreting hydrophilic sericin were obtained after G6 generation.

The results of the observation of the transgenic mutant Ser silkworm obtained from G1 to G6 generations are shown in FIG. 3 . Among them, Figure A is the cross-sectional morphology of the posterior silk gland of the mutant silkworm. The green fluorescence in the outer ring tissue comes from the EGFP in the recombinant protein SER synthesized by the posterior silk gland cells, and the inner green fluorescence shows that the posterior silk gland cells secrete it after synthesis Recombinant protein SER into the lumen of the gland; Figure B is the cross-sectional morphology of the middle silk gland of the mutant silkworm, and the green fluorescence shows the recombinant protein SER transferred from the posterior silk gland cells to the lumen of the middle silk gland; Figure C is the mutant silkworm The silk protein fibers spun out, the green fluorescence shows the recombinant protein SER present in the interior and surface of the silk fibers; Figure D shows the difference in fluorescence between the cocoons made by wild-type and mutant silkworms, and the cocoon silk protein of the mutants has green The fluorescent recombinant protein SER, while the wild-type cocoon silk does not have the characteristic green fluorescence of SER; Figure E shows the visible light images of the corresponding wild-type and mutant silkworm cocoons in Figure D; Figure F shows the wild-type and mutant The difference in fluorescence in the eyes of the 5th instar larvae of the silkworm. The eyes of the larvae of the mutant silkworm show red fluorescence, but the eyes of the wild type silkworm do not. The arrows in the figure indicate the position of the eyes of the larvae.

From the results in Figure 3, it can be seen that the eyes of the larvae of the mutant Ser silkworm show red fluorescence, but the eyes of the wild type silkworm do not show red light fluorescence; the cocoon silk of Ser silkworm shows green fluorescence, but the cocoon silk of the wild type silkworm does not show green fluorescence Photofluorescence; Ser The green fluorescence of recombinant protein SER exists in the posterior silk gland cavity of the 5th instar larvae of Ser silkworm, but there is no green fluorescence of recombinant protein SER in the posterior silk gland cavity of wild-type silkworm.

The content of sericin protein SER3 in the secreted silk protein accumulated in the posterior silk gland cavity of the 5th instar rocking stage larvae of G6 generation Ser silkworm is 4.9%-5.5%, and the content of sericin protein SER3 in the extruded silk protein is 8.8%-10.6%.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention. It should be pointed out that for those of ordinary skill in the art, some improvements can be made without departing from the technical principle of the present invention. and modifications, these improvements and modifications should also be considered as the protection scope of the present invention.

Claims (9)

1. a method for preparing the silkworm whose posterior silk gland can synthesize and secrete hydrophilic sericin, is characterized in that, comprises the following steps: Recombining the DNA molecule encoding the amino acid sequence SER into the silkworm chromosome, expressing and translating to obtain the silkworm silkworm in which the posterior silk gland can synthesize and secrete hydrophilic sericin; Wherein, the nucleotide sequence from the 5' end to the 3' end of the DNA molecule encoding the amino acid sequence SER is the Bombyx mori silk fibroin heavy chain protein Fib-H gene promoter, the Bombyx mori Fib-H gene 5' end signal peptide coding sequence , silkworm sericin protein SER3 coding sequence Ser3 and silkworm Fib-H gene 3' end sequence. 2. The method for preparing the silkworm whose posterior silk gland can synthesize and secrete hydrophilic sericin according to claim 1, characterized in that: the amino acid sequence SER has the amino acid sequence shown in SEQ ID NO:3. 3. the method for preparing the silkworm that the posterior silk gland can synthesize and secrete hydrophilic sericin according to claim 2, is characterized in that: the DNA molecule encoding the amino acid sequence shown in SEQ ID NO: 3 has SEQ ID NO : Nucleotide sequence shown in 4. 4. the rear silk gland according to claim 1 can synthesize and secrete the preparation method of the silkworm of hydrophilic sericin, it is characterized in that, the dna molecular recombination of coding amino acid sequence SER on the silkworm chromosome further comprises the following steps : Constructing a transposable vector comprising a DNA molecule encoding the amino acid sequence SER; and introducing the transposable vector into silkworm eggs. 5. the preparation method of the silkworm that can synthesize and secrete hydrophilic sericin in the posterior silk gland according to claim 4, it is characterized in that: the recombinant gene Ser3 transposition that described transposable carrier is constructed by piggyBac transposon Vector PB-ser. 6. The method for preparing the silkworm whose posterior silk gland can synthesize and secrete hydrophilic sericin according to claim 4 or 5, characterized in that: the transposable carrier has nucleosides shown in SEQ ID NO:5 acid sequence. 7. A transposable vector having a DNA molecule encoding the amino acid sequence shown in SEQ ID NO:3. 8. The transposable vector according to claim 7, characterized in that: the transposable vector is a recombinant gene Ser3 transposable vector PB-ser constructed from a piggyBac transposon. 9. The transposable vector according to claim 7 or 8, characterized in that: the transposable vector has the nucleotide sequence shown in SEQ ID NO:5.