The spatial distribution of transcripts of the segmentation gene Fushi tarazu during Coelopa embryonic development

The expression of the Drosophila fushi tarazu (ftz) gene was investigated in the kelp fly, Coelopa frigida. The investigation included the detection of the gene in the genome of the kelp fly and the detection of the transcripts of the gene in unfertilized eggs and embryos. The spatial distribution of ftz$\backslash sp+$ transcripts during normal Coelopa embryonic development was investigated by in situ hybridization.

The results obtained in this study have led to the following conclusions: (1) The genome of the kelp fly, Coelopa frigida contains sequences homologous to the Drosophila ftz$\backslash sp+$ gene. (2) The $ftz\backslash sp+$ gene is probably not expressed maternally in the kelp fly. (3) In the Coelopa embryo the $ftz\backslash sp+$ transcripts are generally distributed during early cleavage; at these stages the transcripts are of low intensity and there seem to be no regional differences. (4) $Ftz\backslash sp+$ transcripts become localized around the periphery of the embryo around the 11$\backslash spth$ nuclear division (syncytial blastoderm); transcripts after the 12$\backslash spth$ nuclear division are generally restricted to a broad region between approximately 10 and 70% of the egg length. (5) After about the 13$\backslash spth$ nuclear division when cell membranes begin to form and even before cells are formed, the parasegmental pattern of $ftz\backslash sp+$ transcript distribution in the seven odd-numbered parasegments becomes more apparent. (6) It appears that by the time segmentation is first obvious and the germ band is fully extended (about 4.5 h of development) the $ftz\backslash sp+$ gene is no longer expressed. (7) Similar results have been observed in Drosophila wild type embryos. Therefore the embryos used in these experiments were expressing the same dipteran gene at the corresponding morphological stages of development.

Some general conclusions that can be drawn from this study are the following: (1) The data obtained on ftz expression graphically illustrate that spatially restricted gene expression can occur even at the syncytial blastoderm stage in the absence of cell membranes. (2) They confirm that a structural association between nuclei and their adjacent cytoplasm exists at this stage.(3) These observations provide direct molecular corroboration for the notion that differences in developmental potential already exist between nuclei prior to the cellular blastoderm completion.