Hypomorphic alleles of gammaCop gene from Drosophila melanogaster display an unexpected expression pattern in mutant eggs, testes and embryos

Abstract

We report an unusual overexpression pattern of the hypomorphic alleles γCop 11a , γCop 14a and γCop 16b of gammaCop gene from Drosophila melanogaster. Each allele contains a distinct short remnant of the P{lacW} transposon located in 5'UTR. Repeated crosses between γCop 14a /γCop 14a females and γCop 11a /γCop 11a or γCop 16b /γCop 16b males proved to be sterile, but the reciprocal ones are fertile.The most severe allele is γCop 14a since a γCop 14a /γCop 14a line cannot be obtained. Remarkably, qRT-PCR performed on mutant eggs, testes and embryos reveals that γCop 11a , γCop 14a and γCop 16b are overexpressed, which is counterintuitive for hypomorphic alleles. Moreover, the expression scale overlaps the hierarchy of the allelic phenotype severity.We found that the folding ΔG values of the mutant 5'UTRs are very low as compared to the folding ΔG value of the wild-type 5'UTR. This thermodynamic context may account for the uncommon expression pattern of the hypomorphic alleles described herein.

Mutations of γCOP Gene Disturb Drosophila melanogaster Innate Immune Response to Pseudomonas aeruginosa

“…The insertion determines a recessive lethal allele as revealed by obtaining precise viable excisions of P{lacW} S 057302 —proof that there is no other hidden mutation in the l(3)S057302 chromosome accountable for the lethal phenotype [ 28 ]. Moreover, we found that γCOP S057302 fails to complement the lethality of γCOP ∆114 (located in a chromosome 3 with a different mutational background than l(3)S057302 ), confirming data of Jayaram et al [ 29 ] and the fact that γCOP is indeed an essential gene, being also involved in fruit flies’ fertility [ 30 ]. The crosses among γCOP 14a /γCOP 14a males and females are always sterile, but both homozygous males and females are fertile when crossed with flies having at least one wild-type (WT) copy of γCOP ( γCOP WT ).…”

“…The data fit the same hierarchy of the allelic severity scale that we previously reported for lethality and sterility of these γCop alleles [ 30 ]. Therefore, the phenotypic severity modulation of lethality, sterility, and commensal microbiota load are reasonably accountable for the differences between the two alleles of γCOP .…”

“…Since the γCOP S057302 /TM6B strain contains a null allele and a relocated copy of γCOP WT , impairments of the anterograde and retrograde transport between Golgi and ER may be reasonably considered if the γCOP WT allele’s physiology is disturbed by position effects or by defective trans-interactions. On the other hand, γCOP 14a /γCOP 14a males are homozygous for two hypomorphic alleles [ 30 ]; hence, neither of the two mutant strains contains a typical WT copy of the γCOP gene comparative to the Oregon control flies.…”

“…The overexpression of γCOP in γCOP 14a / γCOP 14a males does not necessarily result in an overproduction of γCOP protein since the γCOP 14a allele proved to be functionally hypomorphic. The qRT-PCR and microarray data show a compensative overexpression of an abnormal mRNA encoded by the γCOP 14a allele, actually conducting a net deficit of the protein comparative to Oregon males [ 30 ]. On the other hand, γCOP S057302 is an embryo lethal null allele, so an upregulation is not expected for it, but it is for the wild-copy allele, by a transvection phenomenon similar to the one reported for the Men gene [ 34 ].…”

“…Our microarray data reveal that the transcription patterns of Toll and Imd/Imd-JNK pathways in γCOP 14a /γCOP 14a males are associated with a significant upregulation of γCOP (3.8079X for the infected males and 2.4478X for the uninfected ones). We previously detected a comparative level of overexpression in testes and the oocytes of γCOP 14a /γCOP 14a individuals, but also in γCOP 14a /γCOP 14a embryos [ 30 ]. These constitutive, correlated expression profiles support once more that γCOP mutant background is, at least partially, responsible for the genes’ expression snapshot noticed in Toll and Imd/Imd-JNK pathways.…”