Expression of the germline markers Vasa/Nanos and germline development in the amphioxus Asymmetron lucayanum
Date Issued
2014
Date
2014
Author(s)
Peng, Li-Ying
Abstract
Germline cells are segregated from somatic cells during multicellular animal development and provide the essential genetic materials for the next generation. Previous studies have categorized the mechanisms of germline specification into two major categories, with one uses localized germ plasm (preformation/maternal inheritance) and the other uses inductive signals (epigenesis/zygotic induction). In cephalochordates, it had long been thought the primordial germ cells (PGCs) are specified by epigenesis. Recent studies in Branchiostoma floridae, Branchiostoma belcheri, and Branchiostoma japonicum have challenged this traditional view by showing the existence of maternal germ plasm that contains conserved germline markers. In this research, I investigated the process of PGC formation in another distantly related cephalochordate species, Asymmetron lucayanum, by examing the expression patterns of germline markers Vasa and Nanos. Asymmetron represents one of the two major genera in Cephalochordata. Unlike Branchiostoma, which forms gonads on both sides of the body, Asymmetron forms gonads only on the right side of its body. I found that Asymmetron germline markers are localized in granular cytoplasm near the vegetal pole of the fertilized eggs. The granules were inherited asymmetrically by a single blastomere during the following cleavages, and this germline marker-positive cell migrated to the posterior growth zone during neurulation. These results are similar to the observations in B. floridae, suggesting that Asymmetron also specifies its PGCs using preformation mechanism. Furthermore, in Asymmetron, I found symmetric distribution of the germline marker vasa under both sides of the somites from the late neurula to the late larva stage. However, after metamorphosis, PGCs became asymmetrically localized only on the right side of the juvenile. This transition indicates that between the late larva and the juvenile adult of A. lucayanum, unknown negative regulator(s) may inhibit PGCs from forming gonads on the left side of the body. Further studies on the left-right differential regulation during gonad development will shed light on the source of the right-sided gonad of A. lucayanum.
Subjects
生殖細胞
Vasa基因
Nanos基因
頭索動物
側殖文昌魚
演化
Type
thesis
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