Abstract: The full coding region of the brain-derived neurontrophic factor（BDNF）gene from the Baiji（Lipotes vexillifer）was amplified by polymerase chain reaction（PCR）. The PCR products were cloned into pMD-18T vectors after purification. Then the recombinant plasmids were screened，isolated，and then sequenced. The nucleotide sequences showed an open reading frame（ORF）of 747 bp without any intron. The ORF encoded a protein of 248 amino acids，which contained a signal peptide of 18 amino acids，a prosegment of 111 amino acids，and a mature BDNF of 119 amino acids，respectively.
The nucleotide sequences in the Baiji BDNF coding region had a high level of similarity（> 90%）with those of other mammalians，especially with pig（Sus scrofa）（95%）and cow（Bos taurus）（94.7%）. The amino acids sequence comparison showed that the BDNF precursor proteins of the Baiji had a 94. 5% -99.5% of similarity with other mammalians, indicating a high level of gene conservation of BDNF. In the phylogenetic tree reconstructed based on the neighbour joining (NJ) method with Kimura 2-parameter distance incorporated in computer software MEGA（molecular evolutionary genetics analysis）,species from Orders Cetacea and Carnivora constituted respective monophyletic clades. Further，cetacean species had a relatively closer affinity with ungulates rather than with other mammalians，which is congruent with previous phylogenetic results.

Key words: Baiji(Lipotes vexillifer), BDNF, PCR, Phylogeny, Sequence analysis

摘要： 利用聚合酶链式反应，首次从白鱀豚基因组DNA 中扩增和克隆到脑源神经营养因子的编码区。在该段序列中含有一个长为747 bp 的开放阅读框，无内含子，编码一个由248 个氨基酸组成的蛋白质，预计分子量为27 953.7道尔顿。其中包括由18 个氨基酸残基组成的信号肽区，111 个氨基酸残基组成的前肽区及119 个氨基酸残基组成的成熟区。序列分析表明，白鱀豚脑源神经营养因子基因编码区的核苷酸序列与其它哺乳动物相似性超过90%，而与猪牛相似性相对较高（分别为95% 和94.7%）。氨基酸序列比较发现，白鱀豚BDNF 前体蛋白的氨基酸序列与其它哺乳动物具有94.5% ～99.5%的相似性，显示了极高的保守性。通过邻接法进行的系统发生分析中，鲸目和食肉目的物种分别聚为单系；与其它哺乳动物相比，鲸类与有蹄类的牛和猪的亲缘关系相对较近，这与鲸类和有蹄类之间具有相对较近的亲缘关系相符。

关键词: 白鱀豚, BDNF, PCR, 序列分析, 系统发生