Transforming growth factor-Bs (TGFBs) are candidate genes in the control of chicken
development and growth. It is very important to study the expression, regulation and
functions of these genes.Microsatellites are ideal DNA markers for genetic linkage studies and genome mapping.
An increasing numbers of studies have demonstrated that they may also be involved in
DNA homologous recombination, gene regulation and genome rearrangement in vivo.
The [CAG/CTG]n triplets have an important role in transcriptional factors.We have attempted to clone the 5' region of the chicken TGFB1 gene to facilitate a more
detailed analysis of the expression and developmental role of TGFBs. We have developed
a method for enriching microsatellites in chicken DNA libraries to facilitate the
generation of polymorphic markers and the identification of potential transcriptional
factors.We have shown that chicken TGFB1 exists as an single copy gene with an upper size
limit of approximately 15 to 22 kb. However, screening of a lambda phage chicken
genomic library using both the TGFB1 cDNA and oligo probes failed to obtain chicken
TGFB1 clones.Procedures were developed for the construction of specific microsatellite-enriched DNA
libraries. [CA/TG] n-enriched genomic DNA libraries were constructed using "genetic
marker selection" and DNA affinity hybridisation procedures; whereas [CA/TG] n- and
[CAG/CTG] n-enriched liver cDNA libraries were constructed by a DNA affinity
hybridisation procedure. The frequency of positive clones in the DNA libraries
constructed ranged from 0.5% to 5% depending on the type of microsatellite repeat. An
enrichment of 50 fold over the classical small-insert DNA libraries has been achieved.
Microsatellite-positive clones from both the genomic DNA libraries and the cDNA
libraries were identified and characterised by sequencing. Microsatellite polymorphisms
were studied by polymerase chain reaction and are being mapped using the EAST
LANSING and COMPTON reference mapping crosses. A search of the non-redundant
databases using the available information of expressed sequences revealed chicken
homologues of human transcriptional factor, myocyte enhancer factor 2D (MEF2D) and
human Fragile X syndrome (FMR1) as well as a substantial number of new other genes.
The differential pattern of expression of the chicken MEF2D gene was examined in
different chicken tissues and at various ages. A ubiquitous distribution of chicken
MEF2D transcripts was revealed. Chromosome mapping and a study of the pattern of
expression of these genes is underway. Comparative mapping of closely related avian
species using microsatellite markers from chicken cDNA library is discussed.The isolation of these microsatellites will facilitate the mapping of economically
important quantitative traits in chicken. The mapping of expressed sequences will help to
define candidate genes of these and other traits
