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Characterization of newly generated neurons after an injury to the drosophila adult brain
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Resumo(s)
RESUMO: No cérebro de mamíferos, duas zonas mantêm a capacidade de gerar neurónios durante a vida
adulta, a zona subventricular e a zona subgranular no hipocampo. No entanto, ainda não foram
criadas técnicas que permitam aumentar o potencial neurogénico destas zonas após uma lesão
no cérebro de modo a regenerar o cérebro dos mamíferos.
Para compreender melhor os fatores que influenciam a proliferação das células estaminais
adultas, organismos mais simples, como o peixe-zebra e a mosca-da-fruta, são usados em
investigação. Apesar de se pensar que a neurogénese na mosca adulta era rara, estudos mais
recentes vieram a demonstrar que o cérebro da mosca adulta tem uma elevada capacidade
proliferativa. Após uma lesão no lobo ótico do cérebro da mosca adulta, progenitores
quiescentes são ativados, proliferam e originam novos neurónios, especialmente no local do
dano.
Para determinar os subtipos neuronais formados no cérebro da mosca adulta após uma lesão no
lobo ótico, usei um método de rastreamento de linhagem dependente de recombinação mitótica
para marcar especificamente novos neurónios gerados após a lesão e analisei os seus subtipos
pelas suas assinaturas moleculares de neurotransmissores, fatores de transcrição, e morfologia.
Tendo em conta os perfis moleculares e características morfológicas, descobri que várias classes
de neurónios dos lobos óticos são regeneradas após uma lesão nos mesmos e identifiquei
especificamente o subtipo de neurónios da medula intrínsecos 1, Mi1, que expressam o fator de
transcrição Bsh e que têm um papel importante no processamento de informação visual. Mais
ainda, observei que células da glia também são geradas no lobo ótico e que novos neurónios são
formados no cérebro central após a lesão, no entanto, estudos adicionais são necessários para o
confirmar.
Adicionalmente, questionámo-nos se a resposta regenerativa nos lobos óticos seria relevante
para recuperar funções cerebrais após a lesão. Para o investigarmos, utilizámos um ensaio de
fixação e orientação para determinar se uma lesão no lobo ótico de moscas adultas pode
modificar este comportamento dependente do sistema visual. Os testes comportamentais
revelaram que uma lesão bilateral causa a perda significativa da capacidade de orientação numa
mosca normal. No entanto, esta capacidade foi recuperada uma semana depois da lesão,
sugerindo que os novos neurónios formados após a lesão integram os circuitos visuais e
participam no comportamento de orientação, permitindo uma regeneração funcional do sistema
visual. Para determinar se a recuperação da orientação depende da proliferação de progenitores
neurais adultos, testei o comportamento após a lesão em moscas em que a ativação dos
progenitores neurais e a consequente neurogénese regenerativa são bloqueadas com
ferramentas genéticas específicas. Moscas em que a ativação dos progenitores neurais foi
suprimida demonstraram fraca orientação na fase aguda da lesão e não recuperaram a sua
performance com o tempo. Deste modo, as minhas experiências indicam que a proliferação dos
progenitores neurais adultos e a neurogénese resultante são importantes para recuperar
funcionalmente um comportamento visual após uma lesão cerebral. Em conclusão, estes
resultados enfatizam que a geneticamente acessível mosca da fruta é um modelo promissor para
estudar os mecanismos que regulam a neurogénese adulta e a regeneração funcional do sistema
nervoso central.
ABSTRACT: In the mammalian brain there are two known regions that maintain the ability to generate neurons in the adult, the subventricular zone and the subgranular zone in the hippocampus. However, there are still no successful approaches to enhance the neurogenic potential of these zones after brain injury to regenerate the mammalian brain. To understand the influence of the tissue environment on adult stem cell proliferation, simpler organisms, such as the zebrafish and the fruit fly have been used. Although adult neurogenesis in Drosophila was thought to be scarce, recent studies have shown that the adult brain has proliferative capacity. Acute optic lobe injury in the adult fly brain can trigger proliferation of quiescent progenitor cells to generate new neurons, mainly in the damaged site. To determine the neuron subtypes formed in the fly adult brain after a stab lesion to the optic lobe, I used a mitotic recombination-dependent lineage tracing method to specifically label adult-born neurons after injury and analyzed their identity and differentiation by profiling their neurotransmitter and transcription factor signatures and morphology. Based on molecular profiling and morphological tracing, I have found that injured optic lobes in the adult fly brain regenerate several classes of optic lobe neurons and specifically identified a subtype of medulla intrinsic neurons, the Mi1, which express the Bsh identity transcription factor and are important to process visual information. Furthermore, I also observed glial cells being generated in the optic lobe and new neurons being formed in the central brain after optic lobe injury, however further studies are needed to confirm this. Additionally, I questioned whether the regenerative response in the optic lobes was relevant for recovery of brain function after injury. To this end, I used an assay of fixation and orientation to assess how a visually guided behavior is modified by an injury to the eye of wild-type flies. The behavioral tests revealed that bilateral stab lesion caused a significant loss in normal flies’ orientation ability, which nevertheless was recovered one week later, suggesting that the newly formed neurons integrate into the visual circuitry and participate in the orientation behavior, allowing for functional regeneration. I tested whether the recovery in orientation was dependent on adult neural progenitor proliferation by assessing the orientation behavior after injury of flies in which neural progenitor activation and therefore regenerative neurogenesis is specifically blocked at adult stage with targeted genetic tools. Flies with suppressed progenitor activation showed poor orientation in the acute phase of the injury and did not show a recovery in performance with time. My experiments suggest that adult neural progenitor proliferation and resulting neurogenesis are important for functional recovery of a visually guided behavior after brain damage. Overall, these results underline that the genetically accessible fruit fly is a powerful model to study the mechanisms underlying adult neurogenesis and functional regeneration of the central nervous system.
ABSTRACT: In the mammalian brain there are two known regions that maintain the ability to generate neurons in the adult, the subventricular zone and the subgranular zone in the hippocampus. However, there are still no successful approaches to enhance the neurogenic potential of these zones after brain injury to regenerate the mammalian brain. To understand the influence of the tissue environment on adult stem cell proliferation, simpler organisms, such as the zebrafish and the fruit fly have been used. Although adult neurogenesis in Drosophila was thought to be scarce, recent studies have shown that the adult brain has proliferative capacity. Acute optic lobe injury in the adult fly brain can trigger proliferation of quiescent progenitor cells to generate new neurons, mainly in the damaged site. To determine the neuron subtypes formed in the fly adult brain after a stab lesion to the optic lobe, I used a mitotic recombination-dependent lineage tracing method to specifically label adult-born neurons after injury and analyzed their identity and differentiation by profiling their neurotransmitter and transcription factor signatures and morphology. Based on molecular profiling and morphological tracing, I have found that injured optic lobes in the adult fly brain regenerate several classes of optic lobe neurons and specifically identified a subtype of medulla intrinsic neurons, the Mi1, which express the Bsh identity transcription factor and are important to process visual information. Furthermore, I also observed glial cells being generated in the optic lobe and new neurons being formed in the central brain after optic lobe injury, however further studies are needed to confirm this. Additionally, I questioned whether the regenerative response in the optic lobes was relevant for recovery of brain function after injury. To this end, I used an assay of fixation and orientation to assess how a visually guided behavior is modified by an injury to the eye of wild-type flies. The behavioral tests revealed that bilateral stab lesion caused a significant loss in normal flies’ orientation ability, which nevertheless was recovered one week later, suggesting that the newly formed neurons integrate into the visual circuitry and participate in the orientation behavior, allowing for functional regeneration. I tested whether the recovery in orientation was dependent on adult neural progenitor proliferation by assessing the orientation behavior after injury of flies in which neural progenitor activation and therefore regenerative neurogenesis is specifically blocked at adult stage with targeted genetic tools. Flies with suppressed progenitor activation showed poor orientation in the acute phase of the injury and did not show a recovery in performance with time. My experiments suggest that adult neural progenitor proliferation and resulting neurogenesis are important for functional recovery of a visually guided behavior after brain damage. Overall, these results underline that the genetically accessible fruit fly is a powerful model to study the mechanisms underlying adult neurogenesis and functional regeneration of the central nervous system.
Descrição
Palavras-chave
Neurogénese adulta induzida por lesão Drosophila melanogaster Orientação visua Regeneração funcional Injury-induced adult neurogenesis Drosophila melanogaster Visual orientation Functional regeneration