To escape predators, geckos can detach their tails and then quickly scramble away, sometimes racing across smooth surfaces that are vertical or even inverted. A new tail grows back within a few months. Researchers sequencing the genome of Schlegel’s Japanese gecko, Gekko japonicus, have pinpointed the genes linked to the little critter’s amazing climbing abilities, as well as tail regeneration and nocturnal vision. The work, published in Nature Communications this week, presents the largest genome of any reptile sequenced to date.
Reptiles have undergone 300 million years of evolution, spreading across the planet and adapting to a diversity of habitats both on land and in the water. With about 1,450 species, geckos make up a quarter of all known lizards. They evolved in a terrestrial niche where selection favored smaller body sizes, agility, and nocturnal habits. Most geckos are able to scale walls and ceilings thanks to adhesive toe pads with microscopic, hair-like projections called setae. While the genomes of several reptilian species have already been sequenced, until now there’s been no genomic data from any member of the Gekkonidae family.
A team led by Xiaosong Gu of Nantong University and Huanming Yang of BGI-Shenzhen sequenced the whole genome of an adult male Japanese gecko. This 2.55 billion base genome is comprised of over 22,487 genes. Among these, the team was able to identify those potentially involved in the gecko’s remarkable clinging skills, low-light visual activity, and regenerative ability.
The setae of geckos are mostly made of proteins called beta-keratins, and previous work showed how beta-keratin genes have been crucial to the evolution of scales, claws, bills, and feathers in reptiles and birds alike. The team found that the size of the beta-keratin gene family is involved in the formation of setae: Gekko japonicus has at least 35 genes for setae beta-keratins, or nearly double that of Anolis lizards. They also found that setae beta-keratins experienced two ancient expansions – once about 100 million years ago and another at about 80 million years ago – which match up with the emergence of setae in the fossil record. A gecko with adhesive toe pads was discovered in 100-million-year-old amber from Myanmar.
Animals that are more active at night share certain characteristics, such as light sensitivity, reduced color vision, high olfaction, and special auditory senses. Proteins called opsins are one of the photosensitive molecules within the photoreceptor cells of the eye. And according to the new work, the transition to a nocturnal lifestyle from a diurnal one is correlated to an opsin gene. They found nine opsin genes in the Gekko japonicus genome, compared to the 20 opsin genes in Anolis lizards.
Furthermore, the team identified 155 genes that are potentially involved in tail regeneration. For example, when they examined tail stump tissue sampled one, three, and seven days post amputation, they found that the expression of PTGIS and PTGS1 increased three days later.