論文摘要
本論文涵蓋盲鰻的分子親緣關係與乳酸去氫酶在脊椎動物的表現與演化兩部份研究。有關盲鰻的分子親緣關係研究中本研究選取以粒線體DNA中之16S rRNA基因部份序列為遺傳標誌，進行親緣關係的分析，此一粒線體DNA片段共包含560個鹼基。實驗中共分析三屬15種盲鰻包括Paramyxine cheni, P. yangi, P. sheni, P. fernholmi, P. taiwanae, P. nelsoni, Eptatretus burgeri, E. carrhatus, E. stoutii, Myxine glutinosa, M. formosa, M. carifous, M. sp1, M. sp2, 及M. sp3等。以八目鰻為外群進行親緣關係樹建構，不管是以鄰近加入法(neighbor-joining)、最大儉約法(maximum parsimony)或最大可能性法(maximum likelihood)皆得到相似的親緣關係樹樹型。其中盲鰻亞科(Myxinidae)與黏盲鰻亞科(Eptatretidae)分別形成一單系群，而准盲鰻屬(Paramyxine)則為一多系群。由此分子親緣關係樹所得的結果與以根據形態特徵認為盲鰻的演化由多鰓孔演化為單鰓孔的假說並不一致。具五對鰓孔的P. cheni是黏盲鰻亞科位於親源關係樹最基部的種類。另外，本研究在台灣東北角海域發現一形態特殊的盲鰻，其體表為粉紅色，與產於紐西蘭的E. eso相似。經遺傳親緣關係分析後，發現其親緣關係與現今已知種類差異非常大，應屬一較原始的系群，因此將其描述為一新屬新種Rubicundus oligopores.
為了解乳酸去氫酶(lactate dehydrogenase, LDH)在爬蟲類與鳥類的表現與分布，特以同功異構酶染色法分析蜥蜴及鳥類的腦、眼、心臟、肝臟、骨骼肌肉以及睪丸等組織，發現乳酸去氫酶的分布與表現具有組織專一性，鳥類及蜥蜴除了具有脊椎動物都具備的LDH-A及LDH-B外，在分析31種鳥類及7種蜥蜴樣本中發現其中有8種鳥類和4種蜥蜴具有過去僅在哺乳類發現之第三種乳酸去氫酶(LDH-C)的表現。這與過去認為鳥類及爬蟲類沒有LDH-C的假說不同。
在LDH基因的選殖上以盲鰻為材料，得到一cDNA序列共包含1029個鹼基對，其中1026個為coding region，推導成胺基酸序列後與現有已知之LDH序列進行排序比對及親緣關係分析，盲鰻的胺基酸序列共有341個胺基酸，其中在第220位置起較其他物種的LDH多出8個胺基酸。與其他已知脊椎動物LDH序列進行比較後，發現此一盲鰻LDH基因序列在其他脊椎動物LDH基因都非常保守的位點上出現13個獨特變異，但這些變異的位點皆不屬於活性中心(active center)。在10個鑑別LDH-A與LDH-B的胺基酸位點上，有4個屬於LDH-A，2個屬於LDH-B，4個兩者都不是。與其他脊椎動物LDH-A相似的是，在C端最後第二個位點上盲鰻LDH序列也缺少一個胺基酸，由上述結果與最大簡約法所建構出來的樹型圖，可以認定此一盲鰻LDH序列屬於LDH-A。
另外由鄰近加入法與最大儉約法所得到親源關係樹，盲鰻LDH基因與八目鰻LDH基因並未聚集在同一個分支上。由鄰近加入法與最大儉約法所得的樹型圖，我們推論乳酸去氫酶的演化自頭索動物到脊椎動物的過程有一次基因複製的事件。而現今已知的硬骨魚LDH-C與爪蟾(Xenopus) LDH-A, LDH-C是由硬骨魚與四足類分離後才產生。

Abstracts
The study included molecular phylogeny of hagfish and evolution of lactate dehydrogenase. The mitochondrial DNA sequences from the large ribosomal RNA gene may be of great value for systematic and phylogenetic studies within families. Partial sequences of the 16S rRNA gene were obtained for comparisons among the following hagfish species, Paramyxine nelsoni, P. sheni, P. taiwanae, P. yangi, P. cheni, Eptatretus burgeri, E. stouii, E. cirrhatus, Myxine glutinosa, M. formosana, M. circifrons, M. sp1 and M. sp2. The boundary of first four Paramyxine species from 16S rRNA sequences is ambiguous; however, they are valid based on our further unpublished isozyme data as well as the gill aperture arrangement pattern. The present molecular data show that the genus Paramyxine is polyphyletic. Eptatretus and Paramyxine form a clade, but their included species can be grouped separately into two different subfamilies, the Myxininae and Eptatretinae. The phylogenetic pattern is not congruent with the number of branchial pouches or branchial apertures proposed by Nelson (1994) and Fernholm (1998), who addressed the evolutionary trend of hagfish as being from polybranchiates to monobranchiates and with all hagfish belonging to a monophyletic group. Furthermore, the larger genetic distance between P. cheni and the other Eptatretinae species suggest that P. cheni could be as a basal taxa in Eptatretinae. A new genus and species of Rubicundus oligoporos collected from the northeastern coast of Taiwan is described here. Rubicundus is distinguished by pink body coloration. Rubicundus oligoporos is a five-gilled species with a three-cusp multicusp on the anterior rows and a two-cusp one on the posterior rows. The putative taxonomic position of Rubicundus is discussed based on mitochondrial 16S rRNA gene fragment sequences.
In order to understand the expression of the multiple LDH isozymes in aves, the brain, eye, heart, liver, muscle, and testis were analyzed. Horizontal starch gel electrophoresis was used to examine isozymes of L-lactate dehydrogenase in 4 families and 7 genera of lizards and 33 aves species assigned to 6 orders. Like all other vertebrates, bords possess 2 fundamental LDH loci (LDH-A and LDH-B). A LDH-C product of the third locus was detected in only 8 species of birds and 4 lizards and, for the first time, was reported from the Passeriformes and lizards. The results of this study and those of other previous research suggest that avian LDH-C, reptile LDH-C, and mammalian LDH-C may be orthologous, and may have been derived from ancestor amniote LDH-A.
The present study has determined a cDNA sequence of LDH-A from the muscle of hagfish, it contains 1428 nucleotides including a protein-encoding sequences of 1026 nucleotides, the 5’(54 nucleotides) and 3’ (342 nucleotides) untranslated region.
The hagfish LDH-A protein that we deduced from the nucleotide sequence is 341 amino acids long. Compared to the other vertebrate LDH, the sequence added 8 amino acids in the low hydrophobicity region at position 220-227. Hagfish LDH unique 9 positions exhibit alternative amino acid those conserved in all vertebrates. None of the alternative amino acids positions makes up the active center. Of the 10 positions that are diagnostic for LDH-A versus LDH-B in the gnathostome vertebrate examined, the hagfish LDH-A sequence resemble LDH-A at four, LDH-B at two, and neither at four. Hagfish LDH, like that of the all vertebrate LDH-As is also missing an amino acid at the penultimate position. The hagfish sequence, with its greater similarity to chordate LDH-A sequence in this region, provides additional evidence that the amino acid was added in the common ancestor of LDH-Bs. Our phylogenetic conclusions that LDH of hagfish muscle is a ancestral LDH-A and the lamprey single locus condition is due to gene loss. Both distance and maximum parsimony analysis strongly reject a relationship of hagfish LDH-A with lamprey LDH.

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