RESUMO
Here we assess the fitness consequences of the replacement of the Hoxa1 coding region with its paralog Hoxb1 in mice (Mus musculus) residing in semi-natural enclosures. Previously, this Hoxa1B1 swap was reported as resulting in no discernible embryonic or physiological phenotype (i.e., functionally redundant), despite the 51% amino acid sequence differences between these two Hox proteins. Within heterozygous breeding cages no differences in litter size nor deviations from Mendelian genotypic expectations were observed in the outbred progeny; however, within semi-natural population enclosures mice homozygous for the Hoxa1B1 swap were out-reproduced by controls resulting in the mutant allele being only 87.5% as frequent as the control in offspring born within enclosures. Specifically, Hoxa1B1 founders produced only 77.9% as many offspring relative to controls, as measured by homozygous pups, and a 22.1% deficiency of heterozygous offspring was also observed. These data suggest that Hoxa1 and Hoxb1 have diverged in function through either sub- or neo-functionalization and that the HoxA1 and HoxB1 proteins are not mutually interchangeable when expressed from the Hoxa1 locus. The fitness assays conducted under naturalistic conditions in this study have provided an ultimate-level assessment of the postulated equivalence of competing alleles. Characterization of these differences has provided greater understanding of the forces shaping the maintenance and diversifications of Hox genes as well as other paralogous genes. This fitness assay approach can be applied to any genetic manipulation and often provides the most sensitive way to detect functional differences.
Assuntos
Aptidão Genética/genética , Proteínas de Homeodomínio/genética , Alelos , Animais , Cruzamento , Feminino , Regulação da Expressão Gênica no Desenvolvimento/genética , Loci Gênicos/genética , Heterozigoto , Proteínas de Homeodomínio/fisiologia , Homozigoto , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Fenótipo , Fatores de Transcrição/genética , Fatores de Transcrição/fisiologiaRESUMO
Gene targeting techniques have led to the phenotypic characterization of numerous genes; however, many genes show minimal to no phenotypic consequences when disrupted, despite many having highly conserved sequences. The standard explanation for these findings is functional redundancy. A competing hypothesis is that these genes have important ecological functions in natural environments that are not needed under laboratory settings. Here we discriminate between these hypotheses by competing mice (Mus musculus) whose Hoxb1 gene has been replaced by Hoxa1, its highly conserved paralog, against matched wild-type controls in seminatural enclosures. This Hoxb1(A1) swap was reported as a genetic manipulation resulting in no discernible embryonic or physiological phenotype under standard laboratory tests. We observed a transient decline in first litter size for Hoxb1(A1) homozygous mice in breeding cages, but their fitness was consistently and more dramatically reduced when competing against controls within seminatural populations. Specifically, males homozygous for the Hoxb1(A1) swap acquired 10.6% fewer territories and the frequency of the Hoxb1(A1) allele decreased from 0.500 in population founders to 0.419 in their offspring. The decrease in Hoxb1(A1) frequency corresponded with a deficiency of both Hoxb1(A1) homozygous and heterozygous offspring. These data suggest that Hoxb1 and Hoxa1 are more phenotypically divergent than previously reported and support that sub- and/or neofunctionalization has occurred in these paralogous genes leading to a divergence of gene function and incomplete redundancy. Furthermore, this study highlights the importance of obtaining fitness measures of mutants in ecologically relevant conditions to better understand gene function and evolution.
Assuntos
Aptidão Genética , Proteínas de Homeodomínio/genética , Fatores de Transcrição/genética , Alelos , Animais , Regulação da Expressão Gênica , Marcação de Genes/métodos , Genótipo , Proteínas de Homeodomínio/biossíntese , Homozigoto , Masculino , Camundongos , Camundongos Transgênicos , Fatores de Transcrição/biossínteseRESUMO
The rapid development and increased availability of novel pharmacologic therapies and pharmaceutical products has amplified the potential for drug exposure during pregnancy. Many drugs are beneficial for disease state management during pregnancy and provide significant fetal and maternal health benefits. However, a paucity of safety data combined with the imprecision of the current risk category system renders risk versus benefit assessment difficult. In response to decades of criticism, the U.S. Food and Drug Administration (FDA) is implementing a new pregnancy and lactation labeling rule designed to improve risk versus benefit assessment of drugs used in pregnant and nursing mothers. These recommendations will provide clear and detailed information for both patients and health care providers, and they will include three main categories: risk summary, clinical considerations, and data. The new labeling rules remove the previous letter risk categorization system (A, B, C, D, X). In this review, we summarize the upcoming FDA labeling changes and discuss their potential consequences on clinical practice.