Sommer R J, Sternberg P W
Howard Hughes Medical Institute, California Institute of Technology, Pasadena 91125.
Dev Biol. 1995 Jan;167(1):61-74. doi: 10.1006/dbio.1995.1007.
During the formation of the vulva in many nematode hermaphrodites or females, pattern formation, induction, and cell specification can readily be studied at a single-cell level. Nematodes thus allow an evolutionary analysis of developmental processes. We have analyzed cell lineages and pattern formation in the vulva equivalence group of six rhabditid nematodes of the genera Oscheius, Rhabditella, Rhabditoides, Pelodera, and Protorhabditis. The comparison of these species with four previously analyzed species of this family reveals evolutionary modification at several levels. The number of vulva precursor cells (VPCs) differ among species. Of the three particular cell lineages (1 degree, 2 degrees, and 3 degrees) generated by the vulva precursor cells in Caenorhabditis, two (2 degrees and 3 degrees) are altered, whereas the third lineage (1 degree) is conserved among the analyzed species. While most vulval lineages are invariant, we observe variability of the 3 degrees lineage in Pelodera with respect to the number of precursor cells adopting this fate and the number of progeny formed. In two species, the 3 degrees lineage generates an asymmetrical set of cells, oriented by the gonad. In Protorhabditis we frequently find animals with an additional or altered set of VPCs forming vulval tissue.
在许多线虫雌雄同体或雌性个体的外阴形成过程中，可以在单细胞水平上轻松研究模式形成、诱导和细胞特化。因此，线虫有助于对发育过程进行进化分析。我们分析了奥氏线虫属、小杆线虫属、拟小杆线虫属、单齿线虫属和原小杆线虫属的六种小杆线虫外阴等效组中的细胞谱系和模式形成。将这些物种与该科之前分析过的四个物种进行比较，揭示了多个层面的进化变化。不同物种中外阴前体细胞（VPC）的数量不同。在秀丽隐杆线虫中，由外阴前体细胞产生的三个特定细胞谱系（1级、2级和3级）中，有两个（2级和3级）发生了改变，而第三个谱系（1级）在所分析的物种中是保守的。虽然大多数外阴谱系是不变的，但我们观察到单齿线虫中3级谱系在采用这种命运的前体细胞数量和形成的后代数量方面存在变异性。在两个物种中，3级谱系产生一组由性腺定向的不对称细胞。在原小杆线虫中，我们经常发现一些动物具有额外的或改变的一组形成外阴组织的VPC。
