A maternal homeobox gene, Bombyx caudal, forms both mRNA and protein concentration gradients spanning anteroposterior axis during gastrulation

Xin Xu, Pin Xian Xu, Yoshiaki Suzuki

Research output: Contribution to journalArticlepeer-review

54 Scopus citations


We have isolated a caudal (cad) homologue from a cDNA library of Bombyx mori embryos. The Bombyx cad cDNA encodes a protein of 244 amino acids. The homology between Drosophila and Bombyx homeodomains is 80%. Similar to Drosophila cad, there is no YPWM peptide sequence along the upstream of homeodomain. Northern blot hybridization with a Bombyx cad probe revealed the presence of single maternal transcript of 2.3 kb. A stronger signal of the transcripts was detected in unfertilized eggs and in eggs up to 36 hours after deposition. The transcripts decreased rapidly by 2 days and a weak signal was maintained until hatching. To analyse its spatial expression pattern, we have established a novel frozen sectioning method for in situ hybridization and immunohistochemistry experiments. The results showed that Bombyx cad transcripts accumulated first in the nurse cells and transferred into the oocyte at a defined time during oogenesis. The maternal transcripts of Bombyx cad formed a concentration gradient spanning the anteroposterior axis during the gastrulation stage and were restricted to the anal pad, the most posterior domain, after 2 days of embryogenesis; the Drosophila cad mRNA revealed the corresponding expression profile during the syncytial blastoderm stage. The Bombyx cad protein was not detected in the ovary and the first 9 hours of eggs, but was first detected evenly during cellular blastoderm stage. During gastrulation, Bombyx cad protein concentration gradients shifted along the anteroposterior axis coinciding with the shifting of the mRNA concentration gradients. This is the first example of a concentration gradient along anteroposterior axis that may be involved in segmentation in insect embryos other than the long germ-band type. A comparison of the timing and conservation of mRNA as well as protein gradient formation in Drosophila and Bombyx might help to explain differences in the body plans and give some clues to elucidate the mechanism and function related to mRNA and protein concentration gradients.

Original languageEnglish
Pages (from-to)277-285
Number of pages9
JournalDevelopment (Cambridge)
Issue number2
StatePublished - Feb 1994
Externally publishedYes


  • Anteroposterior axis
  • Bombyx
  • Evolutionary conservation
  • Immunohistochemistry
  • In situ hybridization
  • Maternal homeobox gene
  • Molecular gradient
  • Novel sectioning method


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