Transdetermination

Shearn A, Davis KT, Hersperger E 1978 Transdetermination of Drosophila imaginal discs cultured in vitro. Dev Biol 65 536-540... 

Nurse Do different IDGFs have the propensity to transdetermine discs to different fates ... 

If the existence of an ordered fate map poses the problem of positional information, the striking phenomena of transdetermination and homeosis unavoidably raise the question of the relation of developmental programs in diverse imaginal discs. Transdetermination was discovered when imaginal disc fragments were cultured. Although each disc normally differ-... 

Transdetermination is an example of metaplasia, the transformation of tissue normally destined for one fate, to a distinct fate. The second major metaplasia in Drosophila is due to a class of mutants called homeotic... 

Fig. 3. Patterns of transdetermination from each disc. Length of arrows reflects transdetermination probabilities. Circled numbers, minimum number of transdetermination steps to mesothorax.

TABLE I. Predicted Relative Transdetermination Frequencies Derived from the Chemical Wave Model Applied to the Blastoderm ... 

Li.2 — A > Li.2 — G means the model predicts transdetermination from the first or second leg to antenna is greater than to genital. Abbreviations are explained in the legend of Fig. 9. 

The same conclusions can be drawn from some regeneration experiments and from the proeess of transdetermination. In these instances it has been demonstrated that the differentiated or determined... 

Transdetermination often leads to the appearance of a phenocopy of a known mutation. Moreover, there are many so-called homeotic mutations in Drosophila (first described by Astaurov in 1927), which cause allotypic organ formation. Ari-stopedia is one example of such a mutation (leg instead of antennal structures are formed). 

The mechanism of transdetermination is not clear. It is, however, known that only cultures with a high rate of proliferation will undergo transdetermination. There is, in fact, a positive correlation between the rate of proliferation and the frequency of transdetermination. Some hypotheses for this were experimentally examined (Hadarn, 1967 Gehring and Nothiger, 1973) ... 

The migration of transdetermined cells was rejected in experiments with tissue transplants from ebony to yellow mutants of Drosophila. The transplanted structures formed were always black, regardless of their transdetermination. 

Fig. 64. Transdetermination in a clone. Cells with black nuclei are of the + +/y sn genotype. Cells with light nuclei are hemi or homozygous for y sn. A cross indicates the transde-termined offspring within the y sn clone. As an example, a differentiated test implant is shown with auto- and allotypic structures. (After Hadom, 1967)...

Transdetermination may be the result of somatic mutation. The frequency of obtained transdeterminations, however, is several orders higher than the frequency of somatic mutations (although this frequency is not known exactly in cultures of proliferating tissues). 

From the above, then, it appears more likely that transdetermination affected the cell s heredity by causing a change at the functional level (Hadorn, 1967 Geh-ring, 1968). 

The discussion above suppose that determination and transdetermination occurred not only on the level of the separate cells, but also on the level of all populations which formed as the result of the proliferation of cells. 

Hadorn, E. (1965). Problems of determination and transdetermination. Brook-haven Symp. Biol. 18, 148-161. 

---