The normal program of gene expression during spore germination in Dictyostelium discoideum is deranged in a germination-defective mutant

Biological and molecular correlates between induced dedifferentiation and spore germination in Dictyostelium

When developing cultures of Dictyostelium discoideum are disaggregated at any time prior to cell wall formation and challenged to reinitiate development, amoebae will progress through the original sequence of morphogenetic stages, but the second time through they will do so in roughly one-tenth the original time, a process known as ‘rapid recapitulation’. However, if disaggregated cells are suspended in nutrient medium, they enter a program of dedifferentiation during which they lose the capacity to rapidly recapitulate after an 80 minute lag period in a process known as ‘erasure’. Here we show that cells that have completed the morphogenetic program and emerge from spore coats in the process of germination have also erased. In addition, the germination-specific 270 gene family is expressed during induced dedifferentiation in a unique fashion, and a germination-defective mutant exhibits a dramatic delay in erasure without concomitant defects in the program of gene regulation accompanying induced dedifferentiation. These results suggest for the first time that induced dedifferentiation and spore germination share some common processes in converting cells from a developmental to vegetative state.

Dictyostelium discoideum gene family contains a long internal amino acid repeat

Two different cDNA clones denoted pTO270-6 and pTO270-11 represent two mRNAs that are developmentally regulated during spore germination in Dictyostelium discoideum. The respective mRNAs are found only during early germination and are not present in other stages of growth or multicellular development. Four different genomic clones that hybridize to sequences that are common to both of the 270 cDNA clones were isolated from Dictyostelium libraries and sequenced. Two are the genes for the two cDNAs, and the other two represent genes that do not seem to be transcribed. All four genomic sequences possess a very unusual internal feature in the deduced protein sequences composed of a monotonous repeat of the tetrapeptide threonine-glutamic acid-threonine-proline. The other portions of the proteins have no homology among themselves. The deduced protein corresponding to the 270-6 gene is very similar to avocado (Persea americana) cellulase. Since cellulose in the spore wall has to be digested during spore germination this suggests that this protein may function as an endo-(1,4)-beta-D-glucanase during germination.