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A complete developmental sequence of a Drosophila neuronal lineage as revealed by twin-spot MARCM.

Yu HH, Kao CF, He Y, Ding P, Kao JC, Lee T - PLoS Biol. (2010)

Bottom Line: By identifying the sequentially derived neurons, we found that the neuroblast serially makes 40 types of AL projection neurons (PNs).These observations substantiate the origin-dependent specification of neuron types.Sequencing neuronal lineages will not only unravel how a complex brain develops but also permit systematic identification of neuron types for detailed structure and function analysis of the brain.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia, United States of America.

ABSTRACT
Drosophila brains contain numerous neurons that form complex circuits. These neurons are derived in stereotyped patterns from a fixed number of progenitors, called neuroblasts, and identifying individual neurons made by a neuroblast facilitates the reconstruction of neural circuits. An improved MARCM (mosaic analysis with a repressible cell marker) technique, called twin-spot MARCM, allows one to label the sister clones derived from a common progenitor simultaneously in different colors. It enables identification of every single neuron in an extended neuronal lineage based on the order of neuron birth. Here we report the first example, to our knowledge, of complete lineage analysis among neurons derived from a common neuroblast that relay olfactory information from the antennal lobe (AL) to higher brain centers. By identifying the sequentially derived neurons, we found that the neuroblast serially makes 40 types of AL projection neurons (PNs). During embryogenesis, one PN with multi-glomerular innervation and 18 uniglomerular PNs targeting 17 glomeruli of the adult AL are born. Many more PNs of 22 additional types, including four types of polyglomerular PNs, derive after the neuroblast resumes dividing in early larvae. Although different offspring are generated in a rather arbitrary sequence, the birth order strictly dictates the fate of each post-mitotic neuron, including the fate of programmed cell death. Notably, the embryonic progenitor has an altered temporal identity following each self-renewing asymmetric cell division. After larval hatching, the same progenitor produces multiple neurons for each cell type, but the number of neurons for each type is tightly regulated. These observations substantiate the origin-dependent specification of neuron types. Sequencing neuronal lineages will not only unravel how a complex brain develops but also permit systematic identification of neuron types for detailed structure and function analysis of the brain.

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Distinct cell counts in different adPN types.Twin-spot clones labeled with GAL4-GH146 (A–G) or acj6-GAL4 (K–M). Upper panels: composite confocal images of sister clones in the AL; lower panels: single focal sections showing no innervation of the magenta glomeruli by the green NB clones, indicating clones derived during birth of the last sibling of the preceding adPN type. The clones shown in (A) and illustrated in (H) reveal the adPN NB makes five VA1lm-targeting PNs following derivation of the last DM6-targeting PN. Illustrations of lineage development for additional twin-spot clones are shown in (I), (J), and (N) to (P). Invariant cell counts were obtained for the majority of NB clones paired with the last sibling of the preceding adPN type (see Tables S3 and S4). These support production of a fixed number of neurons for each multi-cellular adPN type, as summarized in the bottom.
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pbio-1000461-g005: Distinct cell counts in different adPN types.Twin-spot clones labeled with GAL4-GH146 (A–G) or acj6-GAL4 (K–M). Upper panels: composite confocal images of sister clones in the AL; lower panels: single focal sections showing no innervation of the magenta glomeruli by the green NB clones, indicating clones derived during birth of the last sibling of the preceding adPN type. The clones shown in (A) and illustrated in (H) reveal the adPN NB makes five VA1lm-targeting PNs following derivation of the last DM6-targeting PN. Illustrations of lineage development for additional twin-spot clones are shown in (I), (J), and (N) to (P). Invariant cell counts were obtained for the majority of NB clones paired with the last sibling of the preceding adPN type (see Tables S3 and S4). These support production of a fixed number of neurons for each multi-cellular adPN type, as summarized in the bottom.

Mentions: Because the AL glomeruli innervated by primary versus secondary neurons operate through solo or multiple PNs, we wondered if fixed cell counts exist for the multi-cellular adPN types composed of secondary neurons. To answer this question, one needs to count the cells of NB clones. We first analyzed GH146-labeled NB clones and started with the ones homogeneously consisting of VA1lm PNs (the last-derived GH146-positive adPN type; Figure 5A; Table S3). All the NB clones that paired with the last DM6 sibling (the preceding adPN type) and thus carrying an entire set of VA1lm adPNs had five cell bodies. This indicates that there are always five VA1lm PNs made by the adPN NB. And the NB clones paired with the last VM2 sibling (the adPN type preceding DM6) possessed eight neurons that include five VA1lm and three DM6 uniglomerular PNs (Figure 5B; Table S3). In this way, we worked backward to determine the cell numbers for late- to early-derived adPN types. Invariant cell counts were obtained for the majority of NB clones paired with the last sibling of six contiguous PN types, which allowed us to deduce that the adPN NB consistently makes 5 VA1lm, 3 DM6, 2 VM2, 3 VM7, 2 1, and 4 VA1d PNs (Figure 5A–G; Table S3).


A complete developmental sequence of a Drosophila neuronal lineage as revealed by twin-spot MARCM.

Yu HH, Kao CF, He Y, Ding P, Kao JC, Lee T - PLoS Biol. (2010)

Distinct cell counts in different adPN types.Twin-spot clones labeled with GAL4-GH146 (A–G) or acj6-GAL4 (K–M). Upper panels: composite confocal images of sister clones in the AL; lower panels: single focal sections showing no innervation of the magenta glomeruli by the green NB clones, indicating clones derived during birth of the last sibling of the preceding adPN type. The clones shown in (A) and illustrated in (H) reveal the adPN NB makes five VA1lm-targeting PNs following derivation of the last DM6-targeting PN. Illustrations of lineage development for additional twin-spot clones are shown in (I), (J), and (N) to (P). Invariant cell counts were obtained for the majority of NB clones paired with the last sibling of the preceding adPN type (see Tables S3 and S4). These support production of a fixed number of neurons for each multi-cellular adPN type, as summarized in the bottom.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2927434&req=5

pbio-1000461-g005: Distinct cell counts in different adPN types.Twin-spot clones labeled with GAL4-GH146 (A–G) or acj6-GAL4 (K–M). Upper panels: composite confocal images of sister clones in the AL; lower panels: single focal sections showing no innervation of the magenta glomeruli by the green NB clones, indicating clones derived during birth of the last sibling of the preceding adPN type. The clones shown in (A) and illustrated in (H) reveal the adPN NB makes five VA1lm-targeting PNs following derivation of the last DM6-targeting PN. Illustrations of lineage development for additional twin-spot clones are shown in (I), (J), and (N) to (P). Invariant cell counts were obtained for the majority of NB clones paired with the last sibling of the preceding adPN type (see Tables S3 and S4). These support production of a fixed number of neurons for each multi-cellular adPN type, as summarized in the bottom.
Mentions: Because the AL glomeruli innervated by primary versus secondary neurons operate through solo or multiple PNs, we wondered if fixed cell counts exist for the multi-cellular adPN types composed of secondary neurons. To answer this question, one needs to count the cells of NB clones. We first analyzed GH146-labeled NB clones and started with the ones homogeneously consisting of VA1lm PNs (the last-derived GH146-positive adPN type; Figure 5A; Table S3). All the NB clones that paired with the last DM6 sibling (the preceding adPN type) and thus carrying an entire set of VA1lm adPNs had five cell bodies. This indicates that there are always five VA1lm PNs made by the adPN NB. And the NB clones paired with the last VM2 sibling (the adPN type preceding DM6) possessed eight neurons that include five VA1lm and three DM6 uniglomerular PNs (Figure 5B; Table S3). In this way, we worked backward to determine the cell numbers for late- to early-derived adPN types. Invariant cell counts were obtained for the majority of NB clones paired with the last sibling of six contiguous PN types, which allowed us to deduce that the adPN NB consistently makes 5 VA1lm, 3 DM6, 2 VM2, 3 VM7, 2 1, and 4 VA1d PNs (Figure 5A–G; Table S3).

Bottom Line: By identifying the sequentially derived neurons, we found that the neuroblast serially makes 40 types of AL projection neurons (PNs).These observations substantiate the origin-dependent specification of neuron types.Sequencing neuronal lineages will not only unravel how a complex brain develops but also permit systematic identification of neuron types for detailed structure and function analysis of the brain.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia, United States of America.

ABSTRACT
Drosophila brains contain numerous neurons that form complex circuits. These neurons are derived in stereotyped patterns from a fixed number of progenitors, called neuroblasts, and identifying individual neurons made by a neuroblast facilitates the reconstruction of neural circuits. An improved MARCM (mosaic analysis with a repressible cell marker) technique, called twin-spot MARCM, allows one to label the sister clones derived from a common progenitor simultaneously in different colors. It enables identification of every single neuron in an extended neuronal lineage based on the order of neuron birth. Here we report the first example, to our knowledge, of complete lineage analysis among neurons derived from a common neuroblast that relay olfactory information from the antennal lobe (AL) to higher brain centers. By identifying the sequentially derived neurons, we found that the neuroblast serially makes 40 types of AL projection neurons (PNs). During embryogenesis, one PN with multi-glomerular innervation and 18 uniglomerular PNs targeting 17 glomeruli of the adult AL are born. Many more PNs of 22 additional types, including four types of polyglomerular PNs, derive after the neuroblast resumes dividing in early larvae. Although different offspring are generated in a rather arbitrary sequence, the birth order strictly dictates the fate of each post-mitotic neuron, including the fate of programmed cell death. Notably, the embryonic progenitor has an altered temporal identity following each self-renewing asymmetric cell division. After larval hatching, the same progenitor produces multiple neurons for each cell type, but the number of neurons for each type is tightly regulated. These observations substantiate the origin-dependent specification of neuron types. Sequencing neuronal lineages will not only unravel how a complex brain develops but also permit systematic identification of neuron types for detailed structure and function analysis of the brain.

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