A NEW PATTERN OF HEMOGLOBIN SWITCHING IN TELEOST FISH-STUDY OF THE EMBRYONIC HEMOGLOBIN IN THE SCHIZOPYGOPSIS PYLZOVI

In order to investigate the pattern of hemoglobin switching in teleost fish endemic to Qinghai-Tibetan Plateau, the membership composition and gene structure of embryonic hemoglobin were determined using transcriptome data and cloning in S. pylzovi. Then qRT-PCR and whole embryo in situ hybridization were used to detect the expression patterns of hemoglobin genes during embryonic development. The results showed that the embryonic hemoglobin genes of S. pylzovi included hbae1, hbae4, hbbe1, and hbbe3, which all contain 3 exons and 2 introns, and the hbbe1/hbae1 pair was transcribed in a “head-to-head” (3′-5′—5′-3′) fashion, and hbbe3/hbae4 were arranged in a “tail-to-tail” (5′-3′—3′-5′) fashion. Further analysis indicated that the gene loss event has caused the lack of hbae3, hbae5 and hbbe2 genes in schizothoracine fish. The results of qRT-PCR and whole embryo in situ hybridization showed that the expression levels of four embryonic hemoglobin genes increased from the 5th day after fertilization (120 hpf) during the early embryo development stages. However, high expression levels of the hbae4 and hbbe3 genes were found only from the 5th day after fertilization to the hatching stage (216 hpf), and then dropped sharply, and the expression of hbae1 and hbbe1 genes increased from the beginning of hatching stage. This study observed a new pattern of hemoglobin switching in teleost fish, which may be related to the particular evolutionary history and the adaptation of the S. pylzovi to the plateau environment. This findings will lay the foundation for further investigation on the hemoglobin switching and environmental adaptation mechanism of teleost fish.