Rickert Christof, Lüer Karin, Vef Olaf, Technau Gerhard M
Institute of Developmental Biology and Neurobiology, University of Mainz, J.-J.-Becherweg 32,Mainz, Germany.
PLoS One. 2018 Feb 7;13(2):e0191453. doi: 10.1371/journal.pone.0191453. eCollection 2018.
Along the anterior-posterior axis the central nervous system is subdivided into segmental units (neuromeres) the composition of which is adapted to their region-specific functional requirements. In Drosophila melanogaster each neuromere is formed by a specific set of identified neural stem cells (neuroblasts, NBs). In the thoracic and anterior abdominal region of the embryonic ventral nerve cord segmental sets of NBs resemble the ground state (2nd thoracic segment, which does not require input of homeotic genes), and serial (segmental) homologs generate similar types of lineages. The three gnathal head segments form a transitional zone between the brain and the ventral nerve cord. It has been shown recently that although all NBs of this zone are serial homologs of NBs in more posterior segments, they progressively differ from the ground state in anterior direction (labial > maxillary > mandibular segment) with regard to numbers and expression profiles. To study the consequences of their derived characters we traced the embryonic lineages of gnathal NBs using the Flybow and DiI-labelling techniques. For a number of clonal types serial homology is rather clearly reflected by their morphology (location and projection patterns) and cell specific markers, despite of reproducible segment-specific differences. However, many lineages, particularly in the mandibular segment, show a degree of derivation that impedes their assignment to ground state serial homologs. These findings demonstrate that differences in gene expression profiles of gnathal NBs go along with anteriorly directed progressive derivation in the composition of their lineages. Furthermore, lineage sizes decrease from labial to mandibular segments, which in concert with decreasing NB-numbers lead to reduced volumes of gnathal neuromeres, most significantly in the mandibular segment.
沿着前后轴，中枢神经系统被细分为节段性单元（神经节段），其组成适应于区域特异性功能需求。在黑腹果蝇中，每个神经节段由一组特定的已识别神经干细胞（神经母细胞，NBs）形成。在胚胎腹侧神经索的胸部和腹部前部区域，节段性的神经母细胞组类似于基态（第二胸段，不需要同源异型基因的输入），并且连续（节段性）同源物产生相似类型的谱系。三个颚头部节段形成脑和腹侧神经索之间的过渡区。最近的研究表明，尽管该区域的所有神经母细胞都是更后部节段中神经母细胞的连续同源物，但它们在数量和表达谱方面在向前方向（唇节>上颌节>下颌节）上逐渐与基态不同。为了研究它们衍生特征的后果，我们使用Flybow和DiI标记技术追踪了颚部神经母细胞的胚胎谱系。对于许多克隆类型，尽管存在可重复的节段特异性差异，但它们的形态（位置和投射模式）和细胞特异性标记相当清楚地反映了连续同源性。然而，许多谱系，特别是在下颌节段，显示出一定程度的衍生，这阻碍了它们被归类为基态连续同源物。这些发现表明，颚部神经母细胞基因表达谱的差异与它们谱系组成中向前定向的渐进衍生相关。此外，谱系大小从唇节到下颌节段逐渐减小，这与神经母细胞数量的减少一起导致颚部神经节段体积减小，在下颌节段最为明显。
