• 식물조직배양학회지
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• 제24권1호
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• pp.1-35
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• 1997

Fertilized egg, by successive cell divisions, differentiates into different tissues and organs with various structures and functions. Different cells and tissues contain different proteins, products of selective gene expression. Not all the genes in any genomes are equally active, temporal and spatial gene expression being the general rule. Present paper attempts to review the tanscriptional mechanisms or the initiations of transcription from several angles. In some of the organisms the genes in the process of transcription or the genes in the inactive state can be seen under the light microscope. Some bands of Drosophila polytene chromosomes may exhibit a swollen or puff appearance under certain conditions. A puff, unfolded or decondensed form of chromomere, represents sets of intense transcriptional activity or RNA synthesis. The heterochromatic X chromosome whose genes remain inactive in the female mammals can be visualized as a dark staining structure called Barr body, Configuration of chromatin differs between transcribed and nontranscribed chromatin. Modification to the chromatin facilitates RNA synthesis. The movement of large polymerase molecule along the DNA would probably be facilitated if some modifications of the chromatin configuration is effected. Methylation of cytosines in CG sequences is associated with inactive genes. Methylation can play a role in determination of mammalian cells during embryogenesis. Demethylation is necessary for the gene to be expressed during development A histone modification that is also known to be correlated with transcriptional capacity of chromatin is acetylation of the lysine residues of the core histones. Chromatin containing a high level of histone acetylation is very sensitive to DNase 1. For the transcription to occur TBP must first bind to the TATA box. Another TF, TF IIB, then binds to the promoter-TBP complex, facilitating the access of RNA polymerase to the transcription initiation site. As recently as eight years ago researchers assumed that histones were irrelevant to the regulation of gene expression. Histones combine with the DNA to form nucleosome of the chromatin. Histones are vital participant in gene regulation. Histone and basal factors compete for access to TATA box. When DNA is exposed to basal factors before histones are introduced, the basal factors assemble on TATA boxes preventing the access of histones, allowing transcription to occur, for transcription to begin, activator protein at the upstream activation sequence or enhancer must interact with the tail of histone H4 at TATA box and cause the histone role particle to dissociate from the TATA box leading to partial breakup of the histone core particle and allowing the basal factors to bind to the TATA box. New concept of genomic flux in contrast to the old concept of static genome has been developed based on the powerful new molecular techniques. Genomic changes such as repetitive DNAs and transposable elements, it is assumed but not yet proved, may affect some of the developmental patterns that characterize particular cells, tissues, organs, and organisms. In the last decade or so remarkable achievement have been made in the researches of the structures and functions of TFs and the specific target sequences located in promoters or enhancers where these TFs bind. TFs have independent domains that bind DNA and that activate transcription. DNA binding domain of TFs serves to bring the protein into the right location. There are many types of DNA binding domains. Common types of motifs can be found that are responsible for binding to DNA. The motifs are usually quite short and comprise only a small part of the protein structure. Steroid receptors have domains for hormone binding, DNA binding, and activating transcription. The zinc finger motif comprises a DNA binding domain. Leucine zipper consist of a stretch of amino acids with a leucine residue in every seventh position Two proteins form a dimer because they interact by means of leucine zippers on similar α-helical domain. This positions their DNA binding basic domains for interaction with the two halves of a DNA sequence with dyad symmetry of TGACTCA, ACTGAGT.

• Parasites, Hosts and Diseases
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• 제24권2호
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• pp.121-136
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• 1986

Recently there have been some reports on human infections of Echinostoma hortense in Korea. It was found that a few species of freshwater fishes were playing the role of the second intermediate host of E. hortense. However, molluscan intermediate host has not been identified yet in Korea. The present study aimed to establish the life cycle of E. hortense in laboratory. Experimental studies such as egg production from the rat, development of the eggs in vitro, exposure of miracidia to freshwater snails, shedding pattern of cercariae from infected snails, morphology of cercariae, cercarial infection to the second intermediate host and infection of metacercariae to the definitive hosts were done. In addition, epidemiological surveys on the infection status in inhabitants and house rats, and on the natural infection of larval echinostomes in the snails and fishes were carried out along the South Hangang-river. The results obtained were as follows: 1. The eggs deposited from adults in physiological saline were cultivated at room temperature($20{\sim}24^{\circ}C$). The miracidia were firstly observed on 8 days after cultivation, and 85.5% of the eggs contained the mature miracidia on 11 days after cultivation. More than 90% formed the miracidia when cultivated at temperature $22{\sim}27^{\circ}C$. Hatching of the miracidia began on 12 days after cultivation and continued for a week. The size of the miracidia was $103.0{{\times}}51.4{\mu}m$ in average. The motility of the miracidia were active up to 8 hours after shedding, but they were all dead within 10 hours after shedding. 2. A freshwater snail, Radix auricularia coreana was cultivated in aquaria. A hatched $F_1$ snails from the egg masses were exposed to 20 miracidia respectively. Escape of cercariae started on 15 days after infecton. Radix auricularia coreana was experimentally identified as the first intermediate host of E. hortense in Korea. 3. Cercarial shedding started on $15{\sim}20$ days after infection by snail, continued for about 10 days (8.8 days in average). Infected snails were dead within 32 days after the miracidial infection. About 1,335 cercariae($328{\sim}1,994$) per snail were shed in its life, and 119 cercariae in average per snail per day were shed. The cercariae were motile for more than 24 hours, and then squirming at the bottom until death. The body and tail sizes of cercariae were $356{\times}186{\mu}m$ and $510{\times}68{\mu}m$ in average, respectively. The rediae parasitized in the snail hosts were found mainly around the pericardial regions, and their size was $1,575{\times}258{\mu}m$ in average. The numbers of developing cercariae in a mature redia were 14 in average ($7{\sim}20$ in range). The numbers of rediae in a snail were 102 in average on 15 days after miracidial infection and 221 in average on 28 days. 4. Three uninfected Misgurnus anguillicaudatus, less than 6.5cm long were used in for the cercarial infection. They were all exposed with 755 cercariae, and examined at 5-day intervals starting from 10 days after infection. All the fishes were infected with metacercariae of E. hortense and a total of 275 was found infected(36.4%). The metacercariae were fed to rats and the adult worms were obtained on 15 days after infection. 5. The infected rats began to deposit the eggs on 11 days after infection. The number of eggs deposited per day per worm (EPD/worm) was $400{\sim}500$ on 3 weeks after infection and was increased to $1,000{\sim}1,500$ on 4 to 17 weeks, then decreased to 800 on 21 weeks after infection. 6. A total of 745 stool specimens collected from 576 male and 169 female residents of 8 different villages along South Hangang basin was examined. Out of 745 specimens, the eggs of Echinostoma sp. were found in 2 cases (0.3%). Of 34 house rats one showed egg-positive (2.9%). 7. Total 971 Radix auricularia coreana collected from 7 sampling stations were examined for shedding of cercariae. Three snails (0.3%) shed the cercariae of E. hortense. A total of 119 out of 542 freshwater fishes (22.0%) had the metacercariae of E. hortense. The fishes parasitized with the metacercariae were 4 out of 14 examined species. The infection rates of 4 species were 34.1% (106 out of 311) in Misgurnus anguillicaudatus, 30.4% (7 out of 23) in Misgurnus mizolepis, 4.3% (2 out of 46) in Moroco oxycephalus and 22.2% (4 out of 18) in Odontobutis obscura interrupta. In summarizing the above results, the first intermediate host of E. hortense was found as Radix auricularia coreana in Korea. Also, it took about 46 days for the shortest completion of a life cycle of E. hortense in summer; that is, 10 days for miracidial development in eggs, 15 days for cercarial development in the snail, about 10 days for metacercarial development in the second intermediate hosts, and 11 days for the maturation as the adults in the definitive hosts. The natural infection rates of E. hortense in the intermediate hosts were relatively high but those in the definitive hosts were low in the middle areas of South Hangang basin.

• 한국수산과학회지
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• 제17권5호
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• pp.449-470
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• 1984

서해안 금강하구의 내초도에서 1980년 7월부터 1983년 10월까지 맛조개(Solen strictus)의 생식소에 기생한 Bacciger 속 cercaria의 생활사를 구명하고자 sporocyst 및 cercaria의 형태와 발육과정, 기생률을 조사하였다. 또한 제이중간숙주 및 종숙주를 실험실에서 인공감염실험과 함께 내초도자연환경구에서 조사하여 metacercaria와 성충의 발육과정을 조사 연구한 결과 지금까지 밝혀진바 없는 Bacciger harengulae의 생활사가 구명되었다. Bacciger harengulae는 맛조개, 대합, 바지락, 띠조개가 제일중간숙주이고, 밀새우를 제이중간숙주로 하며, 종숙주는 전어, 밴댕이로 밝혀졌다. 맛조개의 생식소에 기생된 성숙한 sporocyst의 크기는 $4.0{\sim}4.3{\times}0.20{\sim}0.21$ mm이고, cercaria는 체부 $270{\times}147{\mu}m$, 미부 $270{\times}147{\mu}m$의 크기로서 꼬리 양측에 27쌍의 강모속과 1개의 강미속은 6본의 가닥으로 되어있다. cercaria의 체내에는 구흡반($52{\times}42{\mu}m$), 인두($32{\times}25{\mu}m$), 복흡반($52{\times}50{\mu}m$)과 2 개의 정소와 V자형의 배설낭이 뚜렷이 나타나며, 화염세포식은 2[(3+3)+(3+3)]=24이다. 3년에 걸쳐 맛조개에 기생하고 있는 cercaria의 평균 기생률은 $9.67\%$ 였는데, 이것은 수온의 변화와는 관계없이 연중기생된다. 기생률이 가장 높은 시기는 수온 $28.8^{\circ}C$인 7월($28.0\%$)이고, 가장 낮은 시기는 수온 $19.5^{\circ}C$인 10월($2.4\%$)이었다. 맛조개의 cercaria 기생률은 각장이 클수록 높았으며, 4.0cm 이하에서는 cercaria가 검출되지 않았다. cercaria가 성숙되는 시기는 년중 수온이 $19.5^{\circ}C$이상 상승하는 $5{\sim}10$월까지며, 수온 $19.5^{\circ}C$이하가 되면 미숙한 cercaria만이 검출된다. Cercaria는 수온 $20^{\circ}C$에서 35시간, $25^{\circ}C$에서는 29시간까지 활력이 있었으며, 생존시간은 각각 71시간, 34시간이었으나 $20^{\circ}C$이하에서는 운동력이 활발하지 못하였다. 맛조개에서 유출된 cercaria를 밀새우에 감염시킨 결과 2{\sim}3시간후에 근육에 기생하였고, 기생한 cercaria는 $7{\sim}8$시간후에 cyst를 형성하였으며, 15일이 경과되어 $420{\times}310{\mu}m$의 성숙한 metacercaria로 발육되었다. 실험실에서 수온 $20^{\circ}C$일때 밀새우의 metacercaria 감염률은 $17.0\%$ 이었고, $25^{\circ}C$때는 $61.0\%$의 높은 감염률을 나타냈으며, 감염된 부위는 제일복절, 두흉부, 제이, 삼, 오복절의 순으로 감염되었다. 내초도의 자연 서식장산 밀새우의 metacercaria 감염률은 수온 $26.5^{\circ}C$인 6월에 $9.6{\sim}11.11\%$, 수온 $28{\sim}29.5^{\circ}C$인 7,8월에는 $1.56{\sim}2.50\%$의 감염률을 나타냈다. metacercaria가 감염된 밀새우를 사육중인 전어에 먹인 결과, 20일후 전어의 장에서 $440{\sim}520{\times}310{\sim}360{\mu}m$의 성충으로 발육되었고, 성숙한 충난은 $20{\sim}24{\times}11{\sim}20{\mu}m$ 크기의 타원형이었다. 실험실에서 검출한 것과 동일한 성충이 내초도의 자연산 전어, 밴댕이에서도 체장과 관계없이 $87.3{\sim}100\%$(평균 $95.2\%$) 검출되었으며, 6, 7월에는 $100\%$ 검출되나, 8, 10월에는 $87.3{\sim}88.9\%$로 그 검출률이 낮아졌다. 전어에서 발육된 성충의 크기와 내부형태를 Yamaguti(1938)가 밴댕이에서 검출한 것과 비교한바, 동일하므로 이 흡충을 Bacciger harengulae로 동정하였다.