Abstract:
                                       Hox gene clusters play an important role in the early embryonic development, tissue differentiation and morphogenesis in animals. 
Megalobrama amblycephala, also
 known as Wuchang fish, is an economically important freshwater fish and widely distributed in lakes in the middle and lower reaches of the Yangtze River in China.In order to explore the 
Hox distribution, evolution and expression patterns in 
M. amblycephala, we conducted a series of analyses based on the whole genome 
M. amblycephala. In the present study, we identified all the 
Hox clusters of 
M. amblycephala from the whole genome data. Combined with the multiple methods, we analyzed chromosome distribution and constructed the 
Hox phylogenetic tree based on protein sequences. In addition, the expression patterns of 
Hox in different tissues were further investigated by calculating the number of transcriptional fragments (FPKM).The results showed that 49 
Hox genes were identified in the genome of 
M. amblycephla, and were divided into 7 groups: 
HoxAa, 
HoxAb, 
HoxBa, 
HoxBb, 
HoxCa, 
HoxCb and 
HoxDa. Transcriptome results indicated that 
M. amblycephala Hox gene family had different expression patterns. There were significant differences in the expression level of all 
Hox genes in the muscle of 
M. amblycephala and 
Danio rerio, while the expression pattern was similar. In the 
HoxA cluster, 
HoxA10
b, HoxA3
a, 
HoxA2
a and 
HoxA1
a were highly expressed in the muscles of 
M. amblycephala, and the expression level was higher than that of 
D. rerio; 
HoxA13
a and 
HoxA13
b are not expressed in the muscle of both of fishes; In the 
HoxB cluster, 
HoxB10
a, 
HoxB9
a and 
HoxB7
a were highly expressed in muscle tissue of 
M. amblycephala, while 
HoxB9
a, 
HoxB8
a, 
HoxB7
a and 
HoxB6
a were highly expressed in muscle tissue of 
D. rerio. In the 
HoxC cluster, 
HoxC9
a, 
HoxC2
a, 
HoxC3
a and 
HoxC6
b are highly expressed in muscle tissue of 
M. amblycephala and 
HoxC8
a and 
HoxC3
a are highly expressed in 
D. rerio, while 
HoxC13
a, 
HoxC12
a,
 HoxC11
a, 
HoxC4
a, 
HoxC1
a, 
HoxC13
b, 
HoxC12
b and 
HoxC11
b are very low or even not expressed in muscle tissue of the two fish species; In the 
HoxD cluster, 
HoxD10
a, 
HoxD9
a and HoxD3
a are highly expressed in muscle tissue of 
M. amblycephala and 
HoxD9
a is highly expressed in
 D. rerio, while the expression levels of 
HoxD13
a, 
HoxD12
a and 
HoxD11
a are not expressed in muscle tissue of 
M. amblycephala and 
HoxD13
a is not expressed in muscle tissue of 
D. rerio. In addition, comparative transcriptome analysis of three embryonic stages and three tissues of 
M. amblycephala indicated that 
HoxA2
a, 
HoxA3
a, 
HoxB9
a, 
HoxB3
a, 
HoxB8
a, 
HoxB1
b, 
HoxB5
a, 
HoxB5
b, 
HoxC3
a and 
HoxC4
a were highly expressed at the juvenile fish, while others showed low or even no expression in muscle, intermuscular bone and connective tissues except 
HoxB7
a, 
HoxB10
a and 
HoxB9
a, 
HoxC3
a and 
HoxC8
a. In the 
HoxD family, 
HoxD9
a, 
HoxD10
a and 
HoxD11
a were expressed in the stage II of embryo. Taken together, these results may lay the foundation for further exploring the function of the 
Hox gene family of 
M. amblycephala, and may also provide reference data for other fish 
Hox studies. In addition, studying the expression patterns of 
Hox in the formation of intermuscular bone of 
M. amblycephala also provides reference and theoretical basis for the study of intermuscular bone in other bony fishes.