The differentiation capacity of isolated loach (Misgurnus fossilis L.) blastoderm.

Experiments on the capacity of the isolated teleost blastoderm to undergo development when cultivated in vitro have revealed species differences in the time of initiation of blastoderm differentiation. Thus the Fundulus blastoderm acquires the ability to develop after being separated from the yolk at the stage of 32 blastomeres (Oppenheimer, 1936) while the blastoderms of pike and of salmon differentiate only after isolation at the blastula stage (Devillers, 1947). These differences have been interpreted as the result of a different ratio between the volume of the cytoplasm and the yolk (Tung, Chang, & Tung 1945); the initiation of the capacity of the blastoderm to develop in vitro being interpreted as a result of the passage of some substances required for differentiation from the yolk into the blastoderm (Oppenheimer, 1936). This hypothesis of Oppenheimer was substantiated by other authors (Tung et al. 1945; Tung, Wu & Tung, 1955; Devillers, 1952), although the nature of these hypothetical substances, the time and the mode of their passage from the yolk into the blastoderm is still unknown. This paper describes work designed to discover the minimum age at which cultured blastoderms of loach {Misgurnus fossilis) could differentiate and to elucidate the factors controlling their capacity to do so. These factors could either be changes in the properties of the blastoderm cells as development proceeds, or substances in the yolk playing a morphogenetic role. It seems very likely that both factors act together. Consequently a blastoderm that is incapable of differentiating acquires after a certain time the capacity to develop in vitro in the absence of yolk. Changes in the potencies of the loach blastoderm in the course of its development in vitro during early embryogenesis and the influence of the culture media were also studied. The blastoderms were explanted at successive stages of cleavage, blastulation and gastrulation.