Tomonori Imamichi

Polymorphic microsatellite loci of the rat (Rattus norvegicus).

The EMBL and GenBank DNA databases were searched for microsatellite sequences of the rat containing dinucleotide repeats of (CA)n and (GA)n. Among those obtained, 23 sequences were analyzed by polymerase chain reaction to examine the size variation of the amplified fragment in inbred rat strains. All of the 23 microsatellite sequences varied in size among the strains tested. The 23 microsatellite loci in a pair of substrains separated from the same progenitor strain were then analyzed. Fragments identical in size were observed in all loci of the two substrains, indicating the stability of the microsatellite over a large number of generations. The microsatellite loci, therefore, should be useful markers for linkage analyses in the rat.

External and Skeletal Observations on a New Lethal Mutant of the Rat: Congenital Osteochondrodysplasia with Systemic Subcutaneous Edema

Abstract Malformed rat newborns showing severe subcutaneous edema were frequently found dead in our Wistar‐Imamichi rat colony. Their family record suggested that this malformation would be an inherited disorder. Experimental crosses of the phenotypically normal litter‐mates revealed that this malformation was a new lethal mutant of the rat, following a single autosomal recessive inheritance. External features and skeletal anomalies of the mutant were carefully checked and compared to those of the phenotypically normal litter‐mates. The comparison revealed that (1) this mutant has a characteristic external appearance that includes shortening of the head, trunk, tail and extremities, systemic subcutaneous edema, protruding of the tongue and cleft palate, (2) the axial bones and appendices are shortened and deformed severely and (3) ossification status of the newborn is delayed in digital bones and advanced in the vertebral centra and arches, stemebrae, choracoid process and talus. Observation of the parturition showed that this mutant is born alive but die shortly after birth because of breathing insufficiency. Based on these observations, this mutant was diagnosed as congenital osteochondrodysplasia with systemic subcutaneous edema (ocd for the gene symbol). The mode of inheritance and the similarities to some genetical disorders of other species, including human, are discussed.

Restriction Fragment Length Polymorphisms Detected in N-ras-Related Sequences of Rats and Their Linkage Analyses

Novel restriction fragment length polymorphisms (RFLPs) in inbred rats were revealed with the human N-ras gene as probe. Three fragments hybridizing to the probe were detected by Southern blot hybridization under highly stringent conditions, and one of the fragments showed variation in inbred rat strains. Furthermore, on hybridization under low-stringency conditions, an additional fragment hybridizing to the probe was observed, and this fragment also showed interstrain variation. These two variant fragments showed different distributions in 27 inbred rat strains and segregated in backcross progeny as codominant alleles of independent single autosomal loci. Therefore, the loci for these RFLPs were namedNras-1 andNras-2, respectively. Analyses of linkages between the RFLPs and 11 other loci revealed that theNras-2 locus was closely linked to thec locus (3.7±2.6%), which belongs to rat linkage group I.

Novel restriction fragment length polymorphism of the growth hormone gene in inbred rats

A novel restriction fragment length polymorphism in inbred rats was detected by Southern blot analysis with rat growth hormone cDNA as a probe. Four alleles, characterized byPstI fragments of 1.2, 1.1, 0.9, and 0.7 kb, respectively, were detected in 27 strains examined. The same distribution of polymorphisms was observed on digestion of DNAs of these strains with three other enzymes,PvuII,HindIII, andBamHI. Moreover, the same differences in length of allelic restriction fragments were obtained with these restriction enzymes as withPstI. These findings suggested that the polymorphism was caused by insertion or deletion of variable DNA segments in the second intron of the growth hormone gene. Linkage analyses using backcross progeny provided no evidence for close linkage between the restriction fragment length polymorphism locus and 10 other loci examined.

Decrease in amylase (EC 3.4.21.4) synthesis in lactating rats.

The amylase (EC 3.4.21.4) and trypsin (EC 3.2.1.1) activities in the pancreas in rats during pregnancy, lactation and after the weaning period, and the secretory responses to a secretagogue (caerulein) in the exocrine pancreas of lactating rats were measured. Trypsin activity increased as lactation progressed and reached twice that of unmated rats in the second half of the lactation period. The amylase activity fell before parturition and failed to recover even after the start of lactation and was significantly decreased throughout the lactation period. The total amount of pancreatic juice produced in the lactating rats was significantly greater than that of unmated rats; the amylase output was significantly less than that of unmated rats. When the pups were removed, amylase activity in the pancreas returned to the value in unmated rats. Furthermore, the amylase activity in lactating rats receiving a daily injection of insulin significantly exceeded that of normal lactating rats. These results indicate that the decrease in amylase activity in lactating rats is due to the reduction of amylase synthesis and there is a possibility that insulin is required for normal or elevated rates of amylase synthesis in lactating rats.

Congenital Abnormalities of the Male Genital Organs in the Newly Established TW Rat Strain

Abstract A newly established rat strain named TW showed congenital abnormalities in the male genital organs at about 47% incidence. These abnormalities included the unilateral or bilateral testicular hypoplasia accompanied with ipsilateral aplasia of the epididymis, ductus deferens and gland of ductus deferens. Most commonly these accessories were completely absent but in some cases the lack was partial. The other accessories such as the seminal vesicle, coagulating gland, and prostate were normal. The female genital organs were normal. The genetical analysis revealed that these defects are transmitted by multiple genes with an incomplete penetrace and a threshold effect. The TW rat provides a useful model for studying the developmental process of the male genital system.

A polymorphism detected in a variable number of tandem repeats (VNTR) of the seminal vesicle secretion (SVS) IV gene in inbred rats

The second intron of the rat SVS IV gene contains a tandem repeat region of 20-bp sequences. This region was amplified using the polymerase chain reaction to detect variations. Three alleles, characterized by amplified fragments of 750, 490, and 390 bp, respectively, were found in 24 strains examined. This variation segregated in F1 and backcross progeny in an autosomal codominant manner. We tentatively designated this locusSvs-4. Analysis of linkages between theSvs-4 locus and other loci revealed that it was closely linked to theSvp-1 (<2.9%) and the a (10.0±6.7%) loci, which belong to rat linkage group IV. TheSvp-1 andSvs-4 loci, however, were differently distributed among the inbred rat strains.

Restriction Fragment Length Polymorphism of Cardiac Myosin Heavy Chain Gene in Rats and Its Strain Distribution

The distribution of an RFLP in EcoRI fragments of the cardiac myosin heavy chain gene among 29 strains of laboratory rats was examined. Southern blot hybridization of rat genomic DNAs with rat cardiac myosin heavy chain cDNA as a probe demonstrated an interstrain variation in one of eight EcoRI fragments. Of the 28 inbred strains examined, 10 had a fragment of 10 kbp, whereas 18 had a fragment of 7.5 kbp. The 15 samples of the remaining strain (Iar: WI outbred stock) had fragments of either 7.5 kbp or 10 and 7.5 kbp, indicating that this strain has maintained heterogeneity of these fragments.

Decrease in insulin secretion in lactating rats.

Changes in plasma insulin concentrations in the pregnancy, lactation and after-weaning period in female rats were investigated. Plasma insulin concentrations increased as pregnancy progressed, but there was a sharp decrease before parturition and the values remained at 20 to 30% of those in virgin rats throughout the lactation period. The concentrations again returned to the same levels as in virgin rats 3 days after completion of lactation. Decreased plasma insulin concentrations during the lactation period were seen in the portal and abdominal veins and in the carotid artery. Plasma insulin concentrations in lactating rats decreased in dose-dependent manner with increased litter sizes, but they returned to the values in the virgin rats when the litter sizes were decreased and lactation stopped. Since the same amounts of insulin secretion as in virgin rats were observed in lactating rats after administration of glucose, it was evident that insulin secretion from the pancreas is suppressed in lactating rats. Because plasma insulin concentrations were not decreased in rats with the galactophores sectioned beforehand even when a sucking stimulus was applied, and there were dose-dependent decreases in the blood glucose levels in abdominal vein and simultaneous stepwise decreases in the portal insulin levels in lactating rats as the litters become larger, it was assumed that drops in peripheral blood glucose levels with milk secretion have an effect on the decreased plasma insulin conccntrations in lactating rats.