Basic Research On Occurrence Mechanism Of Albinism In Sea Cucumber Apostichopus Japonicus (Selenka)

In this thesis, albino and normal sea cucumber Apostichopus japonicus (Selenka) were collected as materials. The comparative studies between albino and normal A. japonicus were applied using biological, histological and molecular biological methods. The occurrence mechanism of albinism in A. japonicus was investigated through biological, histological, and molecular biological angles.1. There was no significant difference of basic nutritional components (moisture, ash, total protein, total fat, and total suger) in the body wall of normal and albino A. japonicus. However, the melanin content in the body wall of normal A. japonicus adults was 16 times as albino adults. The melanin content was 3.12% in the body wall of normal A. japonicus adults, while the melanin content was 0.24% in albino A. japonicus adults. In the juvenile offspring, at the 25, 32, 39, 46 and 53days after fertilization, there was no significant difference of melanin content between normal and albino A. japonicus juveniles. At the 60, 74, 81 and 88 days after fertilization, the melanin content in normal A. japonicus juveniles was significantly higher than albino juveniles. We therefore conclude that the lack of melanin in the body wall was the direct cause of albinism occurrence in A. japonicus.2. The body wall of A. japonicus adults discriminated cuticle, epidermis, and dermis tissue. Compared to normal A. japonicus adults, albino adults had fewer epidermal melanocytes in the body wall. Furthermore, in the melanocytes of albino adults, melanosomes were less dense and non-pigmented pre-melanosomes were presented. The structure of the body wall of A. japonicus juveniles - cuticle, epidermis, and dermis - was already clearly developed. Compared to normal A. japonicus juveniles, albino juveniles had very few epidermal melanocytes in the body wall. Furthermore, in the melanocytes of albino juveniles, melanosomes were less developed and no mature melanosomes were preserned. The melanocytes of albino juveniles contained many non-pigmented pre-melanosomes. We therefore conclude that the lack of melanocytes and melanin synthesis in melanosomes were the histological characteristics of albino A. japonicus.3. The full-length cDNA of A. japonicus MITF was cloned; and the sequence of A. japonicus MITF accorded with the characteristic of bHLHZip transcriptional factor family. In the body wall of albino A. japonicus adults, MITF expression levels were significantly lower than normal adults. The MITF expression levels in the body wall of normal A. japonicus adults were 2.96±0.15 times as albino adults. In the juvenile offspring, at the 25 days after fertilization, there was no significant difference of MITF expression level between normal and albino A. japonicus juveniles. At the 32, 39, 46, 53, 60, 74, 81 and 88 days after fertilization, the MITF expression levels in albino A. japonicus juveniles were significantly lower than normal juveniles. We therefore conclude that MITF gene was an essential regulator in A. japonicus not only for melanocyte development and differentiation, but also for melanin production in melanocyte. The significantly low MITF expression level in A. japonicus was one of the causes of albinism occurrence.4. The full-length cDNA of A. japonicus astacin was cloned; and the sequence of A. japonicus astacin accorded with the characteristic of astacin gene family. In the body wall of albino A. japonicus adults, astacin expression levels were significantly lower than normal adults. The astacin expression levels in the body wall of normal A. japonicus adults were 2.73±0.08 times as albino adults. In the juvenile offspring, at the 25 and 32 days after fertilization, there was no significant difference of astacin expression level between normal and albino A. japonicus juveniles. At the 39, 46, 53, 60, 74, 81 and 88 days after fertilization, the astacin expression levels in albino A. japonicus juveniles were significantly lower than normal juveniles. We therefore conclude that astacin gene participated in the regulation of integument color in A. japonicus. The significantly low astacin expression level in A. japonicus was correlated to albinism occurrence.