Hemoglobin Mechanism Of Hypoxia Toleration In Tibetan Chick Embryo

Tibetan chick acclimatize themselves up to high altitude (4,200 m) and the other breeds in low grounds survive rarely with a low hatchability (3.0%) after incubation under hypoxia of simulated 4,200m. In hypoxia of whole 21 days, the incubation rate of Tibetan chick and Recessive White Feather broiler differed with a greatest disparity from the 4th to the 1 lth day and significantly in other stages but from 1st to 3rd day. Hypoxia in each stage did not reduce significantly survival rate of this stage except hatchability. These two results indicated that the hypoxia in last stage have a key effect on next stage.All exons encoding chick hemoglobins were sequenced to analyze gene polymorphism. The functional mutation of Met-32(B13)-Leu found in aD globin chain was related with hypoxia and the mutation frequency increased with elevated altitudes. In addition, the population with higher mutation frequency had a higher hatchability. The automated homology model building was carried out using crystal structure coordinates of chick HbD. The results indicated that the substitution of Met-32(B13)-Leu provides a more hydrophobic surrounding which lead to higher stability of heme and blood-oxygen affinity of hemoglobin.The incubation under 21-day hypoxia (12% O2) was carried out in Tibetan chick from highland and Recessive White Feather Broiler from low land. The whole embryos from 3rd to 8th day and whole blood from 9th to 18th day was collected to investigated the stage expression profiles of whole seven globins and HIF-1α. The results indicate that, under hypoxia, the major adult αA and β globins become major from 3rd to 8th day while major embryonic π and p globins become minor and minor embryonic e globin become major in both breeds; The minor βH and αD globins also serve as the major fetal globins in the embryo from 9th to 18th day under hypoxia in both breeds.The excessive expression induced by hypoxia (12% 02). not produced by earlier expression of HbA, HbH and HbL, is found as the most important hemoglobin mechanism of hypoxia adaptation and is unique to Tibetan chick. The mutation Met-32D(B13)-Leu act as an important effect on hypoxic toleration after day 9 and in adult stage, instead of days 3-8. Days 3-8 is most important stage for survival under hypoxic condition, which is consistent with the result of stage incubation and expression of HIF-la. The over-expressed HIF-la should be responsible to the earlier exchange of the primitive and definitive erythoid cells, the switch of embryonic and adult globins and the excessive expression of all globins in Tibetan chick by directively regulating such factors as EPO, GATA-1, GATA-2, SP1, Y, NF1 and NFE4.The mutation Met-32D(B13)-Leu has been described for the first time in high land pheasant. The low land red-ring pheasant and high land pheasant belong to different subspecies, thus the same mutation and the similar mutation frequency, providing a confirmation by a large sample, support that Tibetan chick originated from highland red jungfowl.