Comparative Analysis Of The Traits In F₁ Hybrids Of Megalobrama Terminalis???× Culter Alburnus??? And Hypoxia Response Analysis Of CITED3 Genes In Megalobrama Amblycephala

In the current study,F₁ hybrids of black bream?Megalobrama terminalis;MT????×topmouth culter?Culter alburnus;CA?????MT?×CA??were obtained by intergeneric crossing,using female MT from the Dongjiang River and male CA from the Yangtze River System in China.Growth performance,morphological characteristics and intermuscular bone?IB?traits of MT?×CA?were evaluated using comparative analysis with MT,CA,blunt snout bream?Megalobrama amblycephala;MA?,and MA?×CA?F₁ as the control.The results showed that?1?MT?×CA?hybrids were similar to MA?×CA?hybrids in growth performance and grew significantly?P<0.05?faster than the parents did,suggesting a remarkable growth advantage after the age of 1 year.At the 3-year-old stage,the hybrid MT?×CA?had not only marked growth advantages over its parents but also higher weight values than those of MA?×CA?.?2?Most numeric traits of MT?×CA?appeared to be medium.Among countable traits,the numbers of soft ray of anal fin and other traits are within the range of its parents,the average hybrid index is calculated to be 65.00,which show that the countable traits approach to the middle values between MT and CA,while slightly incline to its male parent CA.Of measurable traits,seven traits are significantly different from its parents,the average hybrid index is calculated to be 51.61,which indicates the measurable traits are also close to the middle values.Cluster analysis have revealed that MT?×CA?and MA?×CA?were much closer,the same to the MT and MA,join CA again after the two groups cluster.Three principal components with accumulative variance percentage 56.02%were summarized in principal component analysis,reflected the morphological variations of frame,head and caudal peduncle.Discriminant accuracy was 87.1%¹00.0%by established discriminant functioned of the populations.?3?A total of 127 IBs in MT?×CA?appeared to be intermediate between the number of IBs of the female parent MT?124?and male parent CA?137?,and MT?×CA?had significantly fewer IBs than MA?×CA??133?,suggesting that MT?×CA?has more heterosis than MA?×CA?for the number of IBs.IB morphology was classified into 7 shape categories,and the IB morphological complexity of the hybrid of MT?×CA?was intermediate between its parents.In conclusion,the F₁ hybrid of MT?×CA?had advantageous characteristics,including a growth advantage,excellent morphology and fewer and simpler IBs,making it a hybrid of great commercial value.The CITED3 protein is a non-DNA-binding transcriptional co-regulators that involved in the regulation of various transcriptional responses against hypoxia stress.Here,we characterized two closely related but distinct CITED3 genes?Cited3a and-3b?from blunt snout bream?Megalobrama amblycephala?,which is a hypoxia-sensitive species.Both genes have an open reading frame of 756-bp and 723-bp,encoded a protein of 251 amino acid and 240 amino acid,respectively,and they shared a sequence identity of 67%.In adult fish,both Cited3a and-3b mRNAs were highly expressed in kidney tissues.In contrast,they were hardly detected in the skin,muscle and gonad.During embryogenesis,both Cited3a and-3b mRNAs were maternally deposited in eggs and fluctuated from the zygote to the 44 hpf larvae.Whole-mount in situ hybridization demonstrated that both Cited3a and-3b mRNAs were transcribed at brain,gut and tailbud at 12hpf,and at brain and gut at 24hpf,and at brain at 36hpf embryos.Hypoxic treatment led to up-regulating expression of two CITED3 mRNAs during embryogenesis.Under hypoxia,both Cited3a and-3b mRNAs in the kidney and brain and Cited3a mRNAs in the liver were significantly up-regulated.These results provide new insights into the functional conservation and divergence of CITED3 genes and reveal their responses to hypoxia.