Worm Breeder's Gazette 5(2): 35
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
We have tentatively determined the ancestry of nearly half the cells in the L1, using a combination of videotaping, laser ablation and direct observation. Our results to date cover the majority of the postembryonic stem cells, including the gonad, so the complete cell lineage of a substantial part of the adult nematode is now known. The embryonic stem cells are named in the usual way:- [See Figure 1] So the origins of these blast cells are non-segmental. The grouping of the P cells corresponds to the ventral hypodermal equivalence groups revealed by laser ablation (cf. J.Kimble et al., Worm Meeting, 1979). MSt MSt.aa, MSt.pa. Generate part of the pharynx (including some neurons), the pharyngo-intestinal valve, and some body muscles. MSt. ap, MSt.pp. Generate some body muscles, the four coelomocytes, the postembryonic myoblast M (MSt.apaapp), and the somatic gonad precursors Z1 (MSt.pppaap) and Z4 (MSt.appaap). - Anterior cell deaths are seen (cf. Panagrellus: Sternberg and Horvitz, Newsletter 5 No 1). E Generates the twenty intestinal cells. C C.aa, C.pa. Generate ectoderm (mainly dorsal hypodermis). C.ap, C.pp. Generate posterior body muscles (about thirty). D Generates body muscles (about twenty) which lie in the anterior half of the animal. Divides once, yielding the two germ cells (Z2 and Z3). According to the classical view, each stem cell gives rise to a distinctive tissue type. Although the traditional classification is broadly correct, it must be modified in detail and the notion of absolute separation of tissue type at an early stage is no longer valid. In summary, the novel findings are:- (1) C (previously considered to be ectoderm) yields half ectoderm and half mesoderm. (2) AB yields some muscles and MSt yields some neurons; in both cases, the minor tissue type separates from the major at multiple points and at a late stage. (3) The germ line and somatic components of the gonad are formed from different stem cells.