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The carp cth1 gene, related to the mammalian TIS11 family of primary response genes, encodes a novel fish protein with two putative CCCH zinc fingers. This report describes the RNA expression of this gene during cleavage, blastula and gastrula stages of carp embryos. Cth1 mRNA is present in all cleavage stage blastomeres as a maternal message. After the late blastula stage, the maternal expression decreases, revealing a spot of higher expression at the margin of the blastoderm of the dome stage embryo. Further decrease of the maternal message reveals a ring of cth1 expressing cells at the blastoderm margin from the stage of 40% epiboly onwards. By alpha-amanitin treatment we established that this local cth1 expression is of zygotic origin. At the onset of gastrulation the cells of the cth1 ring involute, starting with those in the shield region, and at approximately 60% epiboly the ring is fully involuted and occupies the hypoblast layer. All cth1 transcripts have disappeared at completion of epiboly. We discuss a possible role for the putative cth1 protein during cleavage and gastrulation.

This report describes the cDNA sequence and embryonic RNA expression pattern of carp Hoxb-1. Carp Hoxb-1 is a labial-like, homeobox-containing gene of the 3' end of the Hox gene cluster. The expression pattern in carp is compared to that of homologs in other vertebrates. As holds for other Hox genes, carp Hoxb-1 is expressed with highest intensity at a sharp anterior boundary, and expression fades out towards posterior. At later stages, gaps were found in the domain. The gene is expressed from late gastrulation onwards, first mainly in the hypoblast but later in all germ layers. Its most prominent expression area is rhombomere 4 (r4) of the hindbrain. Transcripts were also found in the neural tube, mesoderm (lateral, head and presomite), epidermis and neural crest. At 30 hours post fertilization, Hoxb-1 was still expressed in r4, in the anterior trunk neural tube and in the branchial arches posterior to r4. Hox genes are thought to be involved in the specification of positional values along the embryonic anterior-posterior axis, and Hoxb-1 expression in r4 is supposed to be important for specifying the unique identity of this hindbrain segment. The conserved expression in r4 suggests that this is also true for carp Hoxb-1.