ABSTRACT
Rat hypodactyly (hd) is an autosomal recessive mutation manifesting in homozygotes as reduction or loss of digits II and III. We mapped the hd allele to a short segment of chromosome 10, containing 16 genes. None of these genes has been shown to influence limb development yet. In situ hybridization showed no changes in several important patterning genes (Shh, Fgf8, Bmp2, 4, 7). However, we found that expression of cartilage condensation marker Sox9, and Bmp receptor Bmpr1b (acting as an upstream activator of Sox9 expression) is absent from the subepithelial mesenchyme of the digit condensations II and III. The failure of the chondrogenic condensations to extend towards the subepithelial mesenchyme may reduce the size of digit primordia and underlie the subsequent loss of phalanges and reduction of metacarpals/metatarsals in hd rats.
Subject(s)
Extremities , Gene Expression Regulation, Developmental , Homeodomain Proteins/genetics , Limb Buds/abnormalities , Limb Buds/metabolism , Mutation , SOX9 Transcription Factor/metabolism , Animals , Body Patterning/genetics , Bone Morphogenetic Protein Receptors, Type I/genetics , Bone Morphogenetic Protein Receptors, Type I/metabolism , Embryo, Mammalian/anatomy & histology , Embryo, Mammalian/metabolism , Female , Homeodomain Proteins/metabolism , Male , Phenotype , Rats , Rats, Wistar , SOX9 Transcription Factor/geneticsABSTRACT
Sex hormone-binding globulin or ABP/SHBG is an extracellular androgen and oestrogen carrier. In the rat, ABP/SHBG is secreted by Sertoli cells of the testis and is thought to regulate androgen bioavailability in the male reproductive tract. During ontogenesis, ABP/SHBG is expressed in many mesoderm-derived tissues, including interdigital mesenchyme of the developing autopodium. Shbg is thus a candidate for Hd, comprising autopodium (hand and foot) reduction and male sterility resulting from spermatogenesis impairment. Moreover, linkage mapping of Hd revealed that an intragenic marker for Shbg, D10Wox12, was non-recombinant with Hd. Sequencing of the entire coding sequence of Shbg failed to identify any variation in hypodactylous animals, distinct from two control strains. However, RT-PCR analysis revealed a significantly higher level of the Shbg transcript in hypodactylous rats compared to SHR controls. Whether Shbg expression is upregulated due to a cis-acting mutation in regulatory elements of the Shbg gene or it is a secondary result of spermatogenesis failure remains to be determined.
Subject(s)
Genetic Linkage , Mutation/genetics , Sex Hormone-Binding Globulin/genetics , Spermatogenesis/genetics , Testis/metabolism , Animals , Base Sequence , Infertility, Male/genetics , Male , Molecular Sequence Data , Rats , Sex Hormone-Binding Globulin/metabolismABSTRACT
We report the establishment of a hybridization-based marker system for the rat genome based on the PCR amplification of interspersed repetitive sequences (IRS). Overall, 351 IRS markers were mapped within the rat genome. The IRS marker panel consists of 210 nonpolymorphic and 141 polymorphic markers that were screened for presence/absence polymorphism patterns in 38 different rat strains and substrains that are commonly used in biomedical research. The IRS marker panel was demonstrated to be useful for rapid genome screening in experimental rat crosses and high-throughput characterization of large-insert genomic library clones. Information on corresponding YAC clones is made available for this IRS marker set distributed over the whole rat genome. The two existing rat radiation hybrid maps were integrated by placing the IRS markers in both maps. The genetic and physical mapping data presented provide substantial information for ongoing positional cloning projects in the rat.
