Analysis of four achaete-scute homologs in Bombyx mori reveals new viewpoints of the evolution and functions of this gene family.
BACKGROUND
achaete-scute complexe (AS-C) has been widely studied at genetic, developmental and evolutional levels. Genes of this family encode proteins containing a highly conserved bHLH domain, which take part in the regulation of the development of central nervous system and peripheral nervous system. Many AS-C homologs have been isolated from various vertebrates and invertebrates. Also, AS-C genes are duplicated during the evolution of Diptera. Functions besides neural development controlling have also been found in Drosophila AS-C genes.


RESULTS
We cloned four achaete-scute homologs (ASH) from the lepidopteran model organism Bombyx mori, including three proneural genes and one neural precursor gene. Proteins encoded by them contained the characteristic bHLH domain and the three proneural ones were also found to have the C-terminal conserved motif. These genes regulated promoter activity through the Class A E-boxes in vitro. Though both Bm-ASH and Drosophila AS-C have four members, they are not in one by one corresponding relationships. Results of RT-PCR and real-time PCR showed that Bm-ASH genes were expressed in different larval tissues, and had well-regulated expressional profiles during the development of embryo and wing/wing disc.


CONCLUSIONS
There are four achaete-scute homologs in Bombyx mori, the second insect having four AS-C genes so far, and these genes have multiple functions in silkworm life cycle. AS-C gene duplication in insects occurs after or parallel to, but not before the taxonomic order formation during evolution.
Zhou
Qingxiang
Q
The Biotechnology Research Institute, National Engineering of crop germplasm and genetic improvement, Chinese Academy of Agricultural Sciences, Beijing, 100081, China. Qingxiang_Zhou@meei.harvard.edu
Zhang
Tianyi
T
Xu
Weihua
W
Yu
Linlin
L
Yi
Yongzhu
Y
Zhang
Zhifang
Z
D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics*; D012831:Bombyx / Q000196:embryology / Q000235:genetics*; D004625:Embryo, Nonmammalian / Q000378:metabolism; D019143:Evolution, Molecular; D020440:Gene Duplication; D017344:Genes, Insect; D010802:Phylogeny; D011401:Promoter Regions, Genetic; D014921:Wings, Animal / Q000196:embryology
D051792:Basic Helix-Loop-Helix Proteins