TRANSCRIPTIONAL CONTROL OF TEKTIN-A MESSENGER-RNA CORRELATES WITH CILIA DEVELOPMENT AND LENGTH DETERMINATION DURING SEA-URCHIN EMBRYOGENESIS

Previous studies have shown that tektin A, one of three integral filam entous protein components of outer doublet microtubules, is synthesize d in sea urchins in an amount correlating to the length of embryonic c ilia initially assembled or experimentally regenerated. To investigate further the molecular mechanism for the regulation of tektin synthesi s, tektin cDNA clones were used to assess mRNA levels during ciliogene sis, zinc-induced animalization, deciliation-induced regeneration and theophylline-induced elongation. Possibly involved in centriole replic ation, low, near-constant levels of mRNA for all three tektins are pre sent in the unfertilized egg and during cleavage stages. Preceded by n ew synthesis of tektin B and C mRNAs, tektin A mRNA is up-regulated du ring ciliogenesis, but only tektin A mRNA levels correlate directly wi th ciliary length in animalized embryos; the others augment larger, no n-limiting pools of tektins B and C. Tektin mRNAs decrease to steady-s tate levels after ciliogenesis, but are up-regulated again when the em bryos are deciliated, correlating with the length of cilia to be deplo yed. In a species where a 3-fold ciliary length increase can be induce d by theophylline treatment of zinc-arrested embryos, the mRNAs accumu late to proportionately higher levels during arrest but are not transl ated until induction, whereupon they decrease inversely with ciliary e longation. This suggests transcriptional control with respect to mRNA amounts but post-transcriptional control with respect to the expressio n of this phenotype. These data are consistent with a model in which ( 1) tektin filaments serve as linear determinants of microtubule double t structure, and (2) the fixed amount of tektin A mRNA and protein syn thesis consequently limit the length of doublets that can be co-assemb led from larger pools of tektins B and C, tubulin, and other component s.