Chinese Alligator Genome Sequencing Complete
August 10, 2013

Research Team Sequences Genome Of The Endangered Chinese Alligator

April Flowers for - Your Universe Online

Scientists from Zhejiang University in China and  BGI Shenzhen have completed and analyzed the genomic sequence of the endangered Chinese alligator (Alligator sinensis) – the first published crocodilian genome. The findings, published in Cell Research, provide plausible explanations of how terrestrial reptiles adapt to aquatic environments and temperature-dependent sex determination (TSD).

The Chinese alligator is critically endangered with a population of less than 100 in the wild and less than 10,000 captive individuals in the Zhejiang and Anhui Provinces of China. Researchers have put a great deal of effort into uncovering the mysteries of this species because it has unique features that allow them to adapt to living in both aquatic and terrestrial habitats.

The research team collected a Chinese alligator sample from Changxing Yinjiabian Chinese Alligator Nature Reserve in Zhejiang Province, China. Using a whole-genome shotgun strategy – that is, sequencing randomly-derived subsegments whose order and orientation within the whole are unknown until the final assembly of overlapping sequences is completed – they sequenced the genome of the alligator. This yielded a draft sequence of Chinese alligator with the size of 2.3 Gb, and a total of 22,200 genes were predicted.

The researchers report the genomic data demonstrates strong DNA level evidence that explains how the Chinese alligator is able to hold its breath under water for long periods of time. This evidence includes the duplication of the bicarbonate-binding hemoglobin gene, positively selected energy metabolism, and more. In addition, researchers identified the genetic signatures of the powerful sensory system and immune system of the Chinese alligator. The findings also presented evidence for the co-evolution of multiple systems specific to the back-to-the-water transition.

The Chinese alligator exhibits TSD, and does not have sex chromosomes. In the majority of animals, including reptiles, the sex of an embryo is determined by their chromosomes. In animals who exhibit TSD, the sex is determined by the incubation temperature at a specific point  in the embryonic development. The research team found the lack of sex chromosomes rather interesting. This discovery led the team to analyze the evolutionary mechanism of sex chromosomes. The Chinese alligator is the first TSD species whose genome has been sequenced, which the team says will have great implication in resolving sex chromosome evolution.

Shengkai Pan, Project manager from BGI, said, "The accomplishment of the Chinese alligator genome is significant for understanding its adaptation for both aquatic and terrestrial environments, and more importantly, for the conservation of such an endangered species."