A new member of the GM130 golgin subfamily is expressed in the optic lobe anlagen of the metamorphosing brain of Manduca sexta

摘要

During metamorphosis of the insect brain, the optic lobe anlagen generate the proliferation centers for the visual cortices. We show here that, in the moth Manduca sexta, an 80 kDa Golgi complex protein (Ms-golgin80) is abundantly expressed in the cytoplasm of neuroblasts and ganglion mother cells in the optic lobe anlagen and proliferation centers. The predicted amino acid sequence for Ms-golgin80 is similar to that of several members of the GM130 subfamily of Golgi-associated proteins, including rat GM130 and human golgin-95. Homologs of Ms-golgin80 from Drosophila melanogaster, Caenorhabditis elegans, and Brugia malayi were identified through homology sequence search. Sequence similarities are present in three regions: the N-terminus, an internal domain of 89 amino acids, and another domain of 89 amino acids near the C-terminus. Structural similarities further suggest that these molecules play the same cellular role as GM130. GM130 is involved in the docking and fusion of coatomer (COP I) coated vesicles to the Golgi membranes; it also regulates the fragmentation and subsequent reassembly of the Golgi complex during mitosis. Abundant expression of Ms-golgin80 in neuroblasts and ganglion mother cells and its reduced expression in the neuronal progeny of these cells suggest that this protein may be involved in the maintenance of the proliferative state.

>Abbreviation:

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BrdU

5-bromo-2′-deoxyuridine

COP I, II

coatomer proteins that coat vesicles and direct protein and membrane trafficking between early compartments of the secretory pathway in eukaryotic cells

GM130

Peripheral membrane proteins associated with the Golgi bodies.

GMC

ganglion mother cell

Ms-golgin80

The Manduca sexta homolog of the GM130 protein. Other homologs include Rn-GM130 (Rattus norvegicus); Hs-GM130 (Homo sapiens), Dm-golgin90 (Drosophila melanogaster), Ce-golgin107 (Caenorhabditis elegans) and Bm-golgin (Brugia malayi)

PBS

phosphate buffered saline

PBST

phosphate buffered saline containing 0.05% Tween-20

TBST

Tris buffered saline containing 0.05% Tween-20

class="kwd-title">Keywords: Golgi complex proteins, mitosis, Ms-golgin80, neuroblasts, tobacco hornworm class="head no_bottom_margin" id="s1title" style="text-transform: uppercase;">IntroductionIn insects with complete metamorphosis, the compound eyes are present only in adults. Correspondingly, during metamorphosis, the optic lobes of the brain, which receive inputs from the new compound eyes, must increase dramatically in size. In Lepidoptera, the growth of each optic lobe in its horizontal dimension during metamorphosis is about twenty-fold: the width of the remainder of the protocerebrum increases only eight-fold during this time (). This growth reflects intense mitotic activity in a population of neuronal precursor cells referred to as the optic lobe anlagen.The adult optic lobe is composed of three major cortices and their associated neuropils, the lamina (outermost), the medulla, and the lobula (innermost). Neurons of these three optic lobe cortices are generated by proliferation centers of ganglion mother cells (GMCs). These centers are in turn derived from the optic lobe anlagen, which are aggregations of stem cells (neuroblasts). The optic lobe anlagen are divided into distinct outer and inner optic lobe anlagen during development. The outer optic lobe anlagen gives rise to the lamina and medulla; the inner optic lobe anlagen produces the lobula (; ). provides a schematic overview of these general brain regions during metamorphosis in Lepidoptera. Both symmetric and asymmetric patterns of division have been demonstrated for these populations of neuroblasts (; ). Symmetric divisions of neuroblasts give rise to a new pair of neuroblasts, and contribute to the expansion and maintenance of the stem cell population itself. Asymmetric divisions of neuroblasts, which typically occur at the edges of the optic lobe anlagen, yield a neuroblast and a GMC. The GMCs then undergo a final round of symmetric division, and their progeny are the neurons of the optic lobes (; ).Overview of metamorphosis of the optic lobes of Manduca sexta. Schematic diagrams based on our sectioned material and on descriptions given in . A. Overview of larval brain showing outer optic anlagen highlighted in blue and inner optic anlagen in red. The anlagen are shown in their entirety as they would be seen in wholemount rather than as they would appear in a single section. B. Representative section through a pupal brain showing the outer optic anlagen in blue and the inner optic anlagen in red. C. Top view of the adult brain, showing the distinct lamina, medulla, and lobula of the mature optic lobe. The lamina and medulla are outlined in blue to indicate their origin in the outer optic anlagen. The anterior and posterior portions of the lobula are outlined in red to reflect their origin in the inner optic anlagen. Abbreviations: AC, antennal center of the larval and pupal brain; AL, antennal lobe of the adult brain; aLO, anterior portion of the lobula; CE, compound eye; IOA, inner optic anlagen; LA, lamina; MB, neuropils associated with the mushroom bodies; ME, medulla; OOA, outer optic anlagen; pLO, posterior portion of the lobula; TC, tritocerebrum. Scale bar = 100 µm.