Blood samples from 620 white muscovy ducks from
Putian Guangdong Wenshi Poultry Co. were collected and
stored at 20 ° C. Genomic DNA was extracted according
to the phenol – chloroform method ( SAMBROOK and RUSSEL
2002). DNA concentration and quality were determined
spectrophotometrically at 260 and 280 nm. Only genomic
DNA preparations with A 260 /A 280 ratios of 1.6 – 1.8 were
used.
Twenty nesting birds and 20 laying birds (40 weeks of
age) were selected from the second generation of white
muscovy ducks. Twelve different tissues were sampled
from each duck, including pituitary, hypothalamus, muscular
stomach, glandular stomach, ovary, kidney, liver,
heart, lung, duodenum, pancreas and spleen. All the tissues
harvested were stored in liquid nitrogen immediately
until total RNA extraction.
RNA extraction and cDNA synthesis
Briefl y, tissues were homogenized and a TRIZOL Reagent
kit (TaKaRa Biotechnology Co.) was used to extract
RNAs, according to the manufacturer ’ s protocol. cDNA
samples of tissues were generated from 2 μ g of total RNA
using a PrimeScript RT reagent Kit (TaKaRa Biotechnology
Co.), according to the manufacturer ’ s protocol.
SNP screening and genotyping
The GH gene comprises fi ve exons and four introns (our
laboratory previously cloned the full length cDNA of GH
gene). In this study, several pairs of primers were designed
according to DNA sequence of microsatellites in the 5 ′ -
fl anking region, 5 ′ regulatory region and exons 1 – 5 of the
GH gene. Apart from one SNP in intron 3, no other SNP
was found. Therefore, intron 3 of the GH gene was selected
for genotyping by the PCR single-strand-conformation
polymorphism (SSCP) method. Briefl y, a genomic fragment
of 348 bp representing intron 3 and containing polymorphic
sites of the GH gene was amplifi ed using a pair
of primers ( GH-F/GH-R ) (primers shown in Table 1). The
PCR reaction comprised a 20 μ l reaction volume consisting
of 100 ng muscovy duck genomic DNA, 1 buffer,
200 μ M of each dNTP, 0.5 μ M each primer, and 1 U of
Taq DNA polymerase. The thermal cycling program was
94 ° C for 5 min; 35 cycles of 94 ° C for 30 s, 58 ° C for 30 s,
and 72 ° C for 30 s, and 72 ° C for 10 min. The PCR product
was detected by electrophoresis through a 1.5% agarose
gel stained with ethidium bromide.