Location and alternative splicing of type XIII collagen RNA in the early human placenta

Type XIII collagen is widely distributed in the fetus. It is characterized by complex alternative splicing of its primary transcripts in regions corresponding to nine exons of the gene.

Localization of type XIII collagen mRNAs in early placentas was determined by in situ hybridization. Reverse-transcription-polymerase chain reactions were used to examine alternative splicing of nine exons in villous and decidual mRNAs.

An intense in situ hybridization signal was observed in the fibroblastoid stromal cells of the placental villi. A moderate signal was found in the endothelial cells of developing capillaries and the cells of the cytotrophoblastic columns. Furthermore, mRNAs were detected in the large decidual cells of the decidual membrane and the stromal cells of the gestational endometrium, but not in the epithelial cells in the endometrial glands. Five combinations of exons 3B, 4A, 4B and 5, encoding half of the COL1 domain, were found. The combination lacking exons 3B-5 was the major variant in both villous and decidual mRNAs. Three combinations of exons 12 and 13 encoding the NC2 domain were found, the long variant containing either 12 or 13 sequences being the major variant in the villi while nearly equal amounts of long and short variants lacking both 12 and 13 sequences were observed in the decidua. Four variants of exons 29, 33 and 37, encoding parts of COL3 and NC4, were found as splicing out of exon 37 was not detected. The major variants in both mRNAs were two that lacked exon 29 and either lacked or contained exon 33 sequences.

Type XIII collagen mRNAs were located in the placenta. Due to alternative splicing, the lengths of the COL1 and NC2 domains of this collagen vary from 57 to 104 and from 12 to 34 amino acids, respectively. The COL3 domain varies between 208 and 235 residues, whereas the NC4 is 18 residues.