E93 promotes transcription of RHG genes to initiate apoptosis during Drosophila salivary gland metamorphosis

20-hydroxyecdysone(20E)induced transcription factor E93 is important for larval–adult transition,which functions in programmed cell death of larval obsolete tissues,and the formation of adult new tissues.However,the apoptosis-related genes directly regulated by E93 are still ambiguous.In this study,an E93 mutation fly strain was obtained by clustered regularly interspaced palindromic repeats(CRISPR)/CRISPR-associated protein 9-mediated long exon deletion to investigate whether and how E93 induces apoptosis during larval tissues metamorphosis.The transcriptional profile of E93 was consistent with 3 RHG(rpr,hid,and grim)genes and the effector caspase gene drice,and all their expressions peaked at the initiation of apoptosis during the degradation of salivary glands.The transcription expression of 3 RHG genes decreased and apoptosis was blocked in E93 mutation salivary gland during metamorphosis.In contrast,E93 overexpression promoted the transcription of 3 RHG genes,and induced advanced apoptosis in the salivary gland.Moreover,E93 not only enhance the promoter activities of the 3 RHG genes in Drosophila Kc cells in vitro,but also in the salivary gland in vivo.Our results demonstrated that 20E induced E93 promotes the transcription of RHG genes to trigger apoptosis during obsolete tissues degradation at metamorphosis in Drosophila.

Expression pattern and tissue localization of the class B scavenger receptor BmSCRBQ4 in Bombyx moil

Class B scavenger receptors （SR-Bs） are cell surface glycoproteins involved in various physiological processes in vivo, including the transport and metabolism of lipids, binding and phagoeytosis of xenobiotics, and signaling. But little information is available about silkworm SR-Bs; it is necessary to study these SR-Bs for revealing their function. In this study, we cloned the full-length coding sequence of BrnSCRBQ4, a SR-B gene from the silkworm Bombyx mori L. We found that the BmSCRBQ4 gene consists of nine exons and eight introns, with an open reading frame of 1371 bp encoding 456 amino acids. Gene expression studies determined that BmSCRBQ4 messenger RNA （mRNA） was expressed in unfertilized eggs, during embryonic development and throughout the majority of the larval period. Expression of mRNA was detected in the mid gut, middle silk gland, posterior silk gland, head, integumentum, fat body, testes and the ovaries of the larval B. mori Dazao strain, as well as in the silkworm cell lines BmN and BmE. Protein expression studies found BmSCRBQ4 protein was expressed only in the testes, fat body and middle silk gland of larvae, as well as in the silkworm cell lines BmN and BmE. The BmSCRBQ4 protein showed variability in banding patterns in different tissues and cells when analyzed by Western blotting. Immunohistochemical staining showed that the BmSCRBQ4 protein localizes to the constitutive membranes or cellular membranes of these tissues. These results indicated that BmSCRBQ4 gene may play some physiologically relevant roles at the cell surface in each tissue.

Chromosome-level Genomes Reveal the Genetic Basis of Descending Dysploidy and Sex Determination in Morus Plants

Multiple plant lineages have independently evolved sex chromosomes and variable karyotypes to maintain their sessile lifestyles through constant biological innovation.Morus notabilis,a dioecious mulberry species,has the fewest chromosomes among Morus spp.,but the genetic basis of sex determination and karyotype evolution in this species has not been identified.In this study,three high-quality genome assemblies were generated for Morus spp.[including dioecious M.notabilis(male and female)and Morus yunnanensis(female)]with genome sizes of 301–329 Mb and were grouped into six pseudochromosomes.Using a combination of genomic approaches,we found that the putative ancestral karyotype of Morus species was close to 14 protochromosomes,and that several chromosome fusion events resulted in descending dysploidy(2n=2x=12).We also characterized a~6.2-Mb sex-determining region on chromosome 3.Four potential male-specific genes,a partially duplicated DNA helicase gene(named MSDH)and three Ty3_Gypsy long terminal repeat retrotransposons(named MSTG1/2/3),were identified in the Y-linked area and considered to be strong candidate genes for sex determination or differentiation.Population genomic analysis showed that Guangdong accessions in China were genetically similar to Japanese accessions of mulberry.In addition,genomic areas containing selective sweeps that distinguish domesticated mulberry from wild populations in terms of flowering and disease resistance were identified.Our study provides an important genetic resource for sex identification research and molecular breeding in mulberry.