Analysis of Snake Z-linked Gene Evolution and Development of COI

Analysis of Snake Z-linked Gene Evolution and Development of
COI and Cytb Gene Barcods of Snakes.
Nararat Laopichienpong, Kazumi Matsubara, Lawan Chanhome, Surin Peyachoknagul,
Yoichi Matsuda, and Kornsorn Srikulnath
Abstract
Snakes are carnivorous squamates reptiles that exhibit genetic sex determination with
ZZ/ZW-type sex chromosomes. Comparing with Z and W sex chromosome among various
snakes, heteromorphic sex chromosomes have been found in Colubridae and Viperidae.
However, the changes of W chromosome are not found in primitive snakes (Boidae and
Pythonidae) referring to Z chromosome. In this study, to investigate the pattern of snake Z-linked
genes evolution, partial sequences of six candidate genes (CTNNB1, CCK, GAD2, TAX1BP1,
MYST2, and BRCA1) were cloned and sequenced from fifteen snake species, one species each
from Xenopeltidae (Xenopeltis unicolor), Cylindrophiidae (Cylindrophis ruffus), Pythonidae
(Python bivittatus), Viperidae (Daboia siamensis), Homolopsidae (Homolopsis buccata), six
species from Colubridae (Oligodon fasciolatus, Ahaetulla prasina, Boiga dendrophila,
Gonyosoma oxycephalum, Coelognathus flavolineatus, and Xenochrophis flavipunctatus), and
four species from Elapidae (Naja kaouthia, Naja siamensis, Ophiophagus hannah, and Bungarus
candidus). Mitochondrial COI and Cytb barcoding were conducted to obviously identify snake
species. The results showed that almost all snake species were clearly identified using COI
barcodes with the intra-specific genetic distance for 0–3.7% and interspecific distance for 3.8–
17.6%, although Cytb barcodes has not been completely developed yet. Only partial sequences
(partial sequences of exon10 and 11, and full sequences of intron10) of CTNNB1 gene on Z and
W chromosomes were completely sequenced. Insertion/deletion (indel) and base substitution
were found in intron sequences of CTNNB1Z between male and female of Viperidae,
Homolopsidae, Colubridae, and Elapidae, but not in Xenopeltidae, Cylindrophiidae and
Pythonidae. Moreover, indel was observed in intron sequences of CTNNB1W among Viperidae,
Homolopsidae, Colubridae, and Elapidae, comparing with CTNNB1Z in both male and female.
These results lead to predict that the divergence of the CTNNB1Z/CTNNB1W genes in snakes
occurred independently after Viperidae, Homolopsidae, Colubridae, and Elapidae diverged from
Xenopeltidae, Cylindrophiidae and Pythonidae approximately 112 to 94 million years ago. This
information would be also applied to molecular sexing markers for practically distinguishing
female and male snakes with various species tested.
Reference
Matsubara, K., H. Tarui, M. Toriba, K. Yamada, C. Nishida-Umehara, K. Agata and Y.
Matsuda. 2006. Evidence for different origin of sex chromosomes in snakes, birds, and
mammals and step-wise differentiation of snake sex chromosomes. Proc. Natl. Acad.
Sci. USA 103: 18190–18195.

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