Abstract
BackgroundIn the decapod crustacean brain, neurogenesis persists throughout the animal's life. After embryogenesis, the central olfactory pathway integrates newborn olfactory local and projection interneurons that replace old neurons or expand the existing population. In crayfish, these neurons are the descendants of precursor cells residing in a neurogenic niche. In this paper, the development of the niche was documented by monitoring proliferating cells with S-phase-specific markers combined with immunohistochemical, dye-injection and pulse-chase experiments.ResultsBetween the end of embryogenesis and throughout the first post-embryonic stage (POI), a defined transverse band of mitotically active cells (which we will term 'the deutocerebral proliferative system' (DPS) appears. Just prior to hatching and in parallel with the formation of the DPS, the anlagen of the niche appears, closely associated with the vasculature. When the hatchling molts to the second post-embryonic stage (POII), the DPS differentiates into the lateral (LPZ) and medial (MPZ) proliferative zones. The LPZ and MPZ are characterized by a high number of mitotically active cells from the beginning of post-embryonic life; in contrast, the developing niche contains only very few dividing cells, a characteristic that persists in the adult organism.ConclusionsOur data suggest that the LPZ and MPZ are largely responsible for the production of new neurons in the early post-embryonic stages, and that the neurogenic niche in the beginning plays a subordinate role. However, as the neuroblasts in the proliferation zones disappear during early post-embryonic life, the neuronal precursors in the niche gradually become the dominant and only mechanism for the generation of new neurons in the adult brain.
Highlights
In the decapod crustacean brain, neurogenesis persists throughout the animal’s life
Our data suggest that the lateral proliferative zone (LPZ) and medial proliferative zone (MPZ) are largely responsible for the production of new neurons in the early post-embryonic stages, and that the neurogenic niche in the beginning plays a subordinate role
By E40% and in subsequent embryonic stages, six to eight NBs and their progeny cluster in the emerging deutocerebrum; these clusters transform into a bilaterally arranged transverse band of BrdU+ cells towards the end of embryogenesis (Figure 4). We will call this transient band of cells the ‘deutocerebral proliferative system’ (DPS) because, as we will show in the following, it gives rise to the LPZ and MPZ that we see in the adults as well as the migratory streams that connect these proliferation zones with the neurogenic niche
Summary
The central olfactory pathway integrates newborn olfactory local and projection interneurons that replace old neurons or expand the existing population. In crayfish, these neurons are the descendants of precursor cells residing in a neurogenic niche. Post-embryonic neurogenesis in a decapod crustacean was first shown in the spider crab Hyas araneus (Decapoda, Brachyura) by labeling with the S-phase cell cycle marker 5-bromo-2’-deoxyuridine (BrdU) [11]. Studies on the adult brain demonstrated persistent neurogenesis in the central olfactory pathway of the adult shore crab, Carcinus maenas [17], and crayfish, Cherax destructor [18], where it was related to a turnover of peripheral olfactory receptor neurons on the antenna 1 [19]. Adult neurogenesis in the olfactory system of decapod crustaceans has been confirmed in nine species: Cancer pagurus, C. maenas, C. destructor, H. americanus, H. araneus, Libinia emarginata, Pagurus bernhardus, Panulirus argus, and Sicyonia brevirostris, suggesting that this is a common phenomenon in this group of organisms [11,13,14,16,17,18,20,21,22,23,24,25,26,27,28,29]
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