title: Mitochondrial structure and dynamics as critical factors in honey bee (Apis mellifera L.) caste development.
abstract: The relationship between nutrition and phenotype is an especially challenging question in cases of facultative polyphenism, like the castes of social insects. In the honey bee, Apis mellifera, unexpected modifications in conserved signaling pathways revealed the hypoxia response as a possible mechanism underlying the regulation of body size and organ growth. Hence, the current study was designed to investigate possible causes of why the three hypoxia core genes are overexpressed in worker larvae. Parting from the hypothesis that this has an endogenous cause and is not due to differences in external oxygen levels we investigated mitochondrial numbers and distribution, as well as mitochondrial oxygen consumption rates in fat body cells of queen and worker larvae during the caste fate-critical larval stages. By immunofluorescence and electron microscopy we found higher densities of mitochondria in queen larval fat body, a finding further confirmed by a citrate synthase assay quantifying mitochondrial functional units. Oxygen consumption measurements by high-resolution respirometry revealed that queen larvae have higher maximum capacities of ATP production at lower physiological demand. Finally, the expression analysis of mitogenesis-related factors showed that the honey bee TFB1 and TFB2 homologs, and a nutritional regulator, ERR, are overexpressed in queen larvae. These results are strong evidence that the differential nutrition of queen and worker larvae by nurse bees affects mitochondrial dynamics and functionality in the fat body of these larvae, hence explaining their differential hypoxia response.
authors.affiliation: Departamento de Biologia Celular e Molecular, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes 3900, 14049-900, Ribeirão Preto, São Paulo, Brazil. Electronic address: douglaselias@usp.br.
authors.forename: Douglas Elias
authors.initials: DE
authors.lastname: Santos
authors.affiliation: Departamento de Física e Química, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Av. do Café, s/n, 14040-903, Ribeirão Preto, São Paulo, Brazil. Electronic address: alberici@fcfrp.usp.br.
authors.forename: Luciane Carla
authors.initials: LC
authors.lastname: Alberici
authors.affiliation: Departamento de Biologia Celular e Molecular, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes 3900, 14049-900, Ribeirão Preto, São Paulo, Brazil. Electronic address: klaus@fmrp.usp.br.
authors.forename: Klaus
authors.initials: K
authors.lastname: Hartfelder
mesh_terms: D000818:Animals; D001516:Bees / Q000235:genetics / Q000254:growth & development / Q000502:physiology* / Q000648:ultrastructure; D019069:Cell Respiration; D005216:Fat Body / Q000166:cytology / Q000648:ultrastructure; D005260:Female; D018507:Gene Expression Regulation, Developmental; D019476:Insect Proteins / Q000235:genetics* / Q000378:metabolism; D007814:Larva / Q000235:genetics / Q000254:growth & development / Q000502:physiology / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D008928:Mitochondria / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: D019476:Insect Proteins; D014157:Transcription Factors; D010100:Oxygen
keywords: High-resolution respirometry; Honeybee; Hypoxia response; Mitochondrial transcription factors; Queen development