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A Shum-Siu

Publications and source records attributed to A Shum-Siu.

6 recordsLinked to original sources
PubMed2006

Inter-enlargement pathways in the ventrolateral funiculus of the adult rat spinal cord.

The ventrolateral funiculus (VLF) in the spinal cord contains important ascending and descending pathways related to locomotion and interlimb coordination. The primary purpose of this descriptive study was to investigate the distribution of inter-enlargement pathways in the adult rat spinal cord with an emphasis on the VLF. We made discrete unilateral injections of Fluoro-Gold (FG) into the right VLF at thoracic segment (T) 9, and either unilateral or bilateral injections of Fluoro-Ruby (FR) into the intermediate gray matter at the cervical (C) 5-6, C7-8, or lumbar (L) 2 segmental levels. Inter-enlargement neurons with ascending axons in the right VLF were found bilaterally in laminae VII and VIII throughout the rostral lumbar spinal cord (L1-L3) and predominantly contralaterally in the caudal lumbosacral (L4-S1) spinal cord. Following left unilateral FR injections at C5-6 or C7-8 and right unilateral VLF injections of FG at T9, very few double-labeled neurons could be found anywhere in the lumbar spinal cord. Similar injections of FR at L2 revealed an almost symmetrical bilateral distribution of double-labeled neurons throughout the cervical spinal cord (C1-8). These results describe ascending and descending pathways within the spinal cord that interconnect the two enlargements and involve both commissural and ipsilateral interneurons. The majority of inter-enlargement neurons had axons within the VLF at T9. These observations support the hypothesis that the VLF contains long ascending and descending axons with propriospinal inter-enlargement, commissural and ipsilateral connections that are anatomically well-suited to mediate interlimb coordination.

Animals↗
PubMed1997

Consistent allelic loss on mouse chromosome 7 distal to tyrosinase in 4-nitroquinoline-1-oxide-induced oral cavity tumors with loss of heterozygosity at Ha-ras-1.

We have previously shown that all CBA/J mice exposed to 4-nitroquinoline-1-oxide (4NQO) eventually develop oral cavity squamous cell carcinomas, and two-thirds of these tumors have Ha-ras-1 (Hras1) point mutations at codon 12. Half of the tumors with Hras1 mutations have loss of heterozygosity (LOH) at Hras1. In the study reported here, seven tumors with LOH at Hras1, six heterozygous for Hras1, and six without Hras1 mutations were analyzed to define the extent of LOH on chromosome (Chr) 7. Microsatellite polymorphisms present in CBA/J mice were used as informative allelic markers. Tumors with LOH at Hras1 showed consistent allelic loss at the distal portion of Chr 7. The boundary of allelic loss lay between the tyrosinase and hemoglobin beta chain loci, which are 6 cM apart. None of the tumors that remained heterozygous for Hras1 or had no Hras1 mutations had evidence of chromosomal loss involving Chr 7. Because LOH was only detected in advanced lesions long after exposure to 4NQO had ceased, we presume that the chromosomal alterations by which LOH occurred were independent of the carcinogen exposure. The development of LOH in only half of the tumors with Hras1 point mutations suggests that LOH was not caused by the initial Hras1 point mutation but was a highly selected event during tumorigenesis.

4-Nitroquinoline-1-oxide↗
PubMed1996

Frequent DNA polymorphisms exist in inbred CBA/J and C3H/HeN mice.

Although occasional DNA polymorphisms have been observed in inbred mice, CBA/J and C3H/HeN mice have two microsatellite alleles at over 1/3 of microsatellite loci tested. Since DNA polymorphisms were not detected in DBA/2J, C57BL/6J, and BALB/cJ, the frequency of microsatellite polymorphisms appears to be strain specific. Thus, genetic studies in inbred mice require testing for preexisting polymorphisms. The polymorphisms detected in CBA/J mice appear to be stable and do not represent microsatellite instability or a mutator phenotype. Somatic mosaicism was not observed and no more than two alleles were detected per locus. CBA/J propagated only by brother-sister mating maintained seven of eight polymorphisms over 5 years. These data suggest that the polymorphisms are due to an inherited trait and that the pattern of inheritance is not due to Mendelian distribution. As breeding analysis was not performed, the pattern of allelic inheritance is unknown.

Animals↗
PubMed1994

Detection of epidermal growth factor receptor mRNA in tissue sections from biopsy specimens using in situ polymerase chain reaction.

Human epidermal growth factor (EGF) receptor mRNA was detected in cryopreserved tissue sections adherent to whole glass slides using in situ reverse transcriptase polymerase chain reaction. EGF receptor cDNA was synthesized in situ by reverse transcription using an EGF receptor-specific oligonucleotide primer. In situ polymerase chain reaction amplification in the presence of digoxigenin-11-dUTP and subsequent binding with an antidigoxigenin antibody conjugated to alkaline phosphatase allowed direct visualization. Because DNase, RNase, or proteinase K are not required, tissue integrity is maintained. EGF receptor mRNA is expressed in the basal layer of normal human skin epithelium and is significantly overexpressed in squamous cell tumor specimens, which is consistent with conventional analysis of EGF receptor expression. The assay is semiquantitative, quicker, more sensitive, and void of the nonspecific binding associated with in situ hybridization. In situ reverse transcriptase polymerase chain reaction using whole glass slides is ideally suited for detecting moderate to infrequently expressed transcripts in biopsy specimens.

Antisense Elements (Genetics)↗
PubMed1993

Variation in cellular EGF receptor mRNA expression demonstrated by in situ reverse transcriptase polymerase chain reaction.

Cell to cell variation of epidermal growth factor (EGF) receptor mRNA levels in heterogeneous tissues has been demonstrated with an in situ assay that couples reverse transcriptase with the polymerase chain reaction (in situ RT-PCR). EGF receptor mRNA is consistently more highly expressed in regions where cell division occurs; EGF receptor mRNA is markedly reduced if not absent in areas of squamous cell differentiation. Both human and mouse tumors overexpress EGF receptor mRNA when compared to normal tissue. In situ RT-PCR performed on thin sections obtained from cell pellets of cultured cells with known levels of EGF receptor mRNA expression demonstrated that the mRNA detected is consistent with that observed by Northern analysis and quantitative PCR on isolated RNA and by protein levels detected by antibody binding assays. In situ RT-PCR is significantly more sensitive than in situ hybridization (ISH). The method avoids background associated with hybridization reactions as in ISH or ISH following in situ PCR. In situ RT-PCR appears to be applicable to any gene as long as the oligonucleotide primers used have been proven to be specific and effective in a standard RT-PCR assay.

Animals↗