Multifactorial genetics of exencephaly in SELH/Bc mice.

BACKGROUND: The SELH/Bc mouse strain has 10-30% exencephaly and is an animal model for human neural tube closure defects. This study examined the number of causative genes, their dominance relationships, and linkage map positions. METHODS: The SELH/Bc strain (S) was crossed to the normal LM/Bc strain (L) and frequencies of exencephaly were observed in the F(1), BC(1), and F(2) generations. 102 F(2) males were individually testcrossed by SELH/Bc. The extremes, the 10 highest and 10 zero exencephaly-producing F(2) sires, were typed for 109 SSLP marker loci in a genome screen. Next, the resultant five provisional chromosomal regions were tested for linkage in 31 F(2) exencephalic embryos. Finally, 12 males, SS or LL for the Chr 13 region on an LM/Bc background, were testcrossed by SELH/Bc. RESULTS: The exencephaly frequencies in the F(1) (0.3%), BC(1) (4.4%), and F(2) (3.7%), and the distribution of F(2) males' testcross values (0-15.5%), indicated that the high risk of exencephaly in SELH/Bc is due to the cumulative effect of two or three loci. Linkage studies indicated the location of semidominant exencephaly-risk genes on Chr 13 near D13Mit13 (P < 0.001), Chr 5 near D5Mit168 (P < 0.025), and possibly Chr 11 near D11Mit10 (P < 0.07). The gene on Chr 13, Exen1, and the strong role of other loci were confirmed by the congenic males. CONCLUSIONS: The high risk of exencephaly in SELH/Bc mice is caused by the cumulative effect of two to three semidominant genes. Candidate genes include Msx2, Madh5, Ptch, and Irx1 (Chr 13) and Actb and Rac1 (Chr 5).

Gaping lids, gp, a mutation on centromeric chromosome 11 that causes defective eyelid development in mice.

In mammals, during fetal development, the eyelids grow and flatten over the eyes and temporarily fuse closed. Failure of this normal developmental process in mice leads to the defect, open-eyelids-at-birth. Nearly all newborns of the GP/Bc strain, homozygous for the spontaneous recessive mutation, gaping lids (gp), have bilateral open eyelids at birth, with essentially no fusion between the upper and lower eyelids. Histological sections and scanning electron microscopy of GP/Bc eyes during the normal period of eyelid growth and fusion indicate that gp/gp mutant fetuses have deficient upper and lower eyelids; surface periderm cells that appear to have some role in eyelid growth and fusion are present, but lack a normal "streaming pattern toward the fusion zone. No other defects due to the gaping lids mutation were detected. A genetic analysis based on outcrosses of GP/Bc to various linkage marker stocks and to CBA/J and ICR/Bc normal strains was done. Penetrance in F(2) segregants, but not in BC1 segregants, was usually significantly less than 100%, was strongly affected by the identity of the normal strain used, ranging from 44% to 92%, and indicated a potential complexity of modifiers. Forty-one affected F(2) and 120 BC(1) segregants from the outcross of GP/Bc to CBA/J, and 23 affected F(2) segregants from the outcross to ICR/Bc, were used to map gp to proximal Chr 11 between the centromere and D11Dal1 (Camk2b), an interval previously defined as less than 1 cM. Sets of whole F(2) litters from the crosses to CBA/J (n = 106) and ICR/Bc (n = 65) strains were typed for informative SSLPs near gp (D11Mit62 and D11Mit74, respectively) and demonstrated that the segregation ratios in the region are Mendelian. The known genes in the interval, Nf2 and Lif, do not seem to be obvious candidate genes for gp. An Egfr-null allele was used to confirm the previously reported map position of the potential candidate locus, Egfr, to a more distal interval, between D11Mit62/226 and D11Mit151, from which gp had been excluded. Tests for allelism showed that the Egfr mutation and the gp mutation complement each other, and therefore also indicate that they are at different gene loci. Open-eyelids-at-birth is associated with several mutations at other loci with variable penetrance owing to modifiers and in other more complex genetic liabilities in inbred strains, and the genetics of this trait is a model for other genetically complex developmental threshold traits. The gaping lids mutation identifies a previously unknown locus on proximal Chromosome (Chr) 11 that has a strong role in fetal eyelid growth.

The lidgap-Gates (lgGa) mutation for open eyelids at birth maps to mouse chromosome 13.

Complex nonadditive interactions between specific alleles at multiple loci may underlie many so-called multifactorial threshold birth defects. The open-eyelids-at-birth defect in mice is a good model for these defects, and an understanding of its genetic complexity begins with mapping the participating loci. The open-eyelids defect can be part of a syndrome or can occur with no other obvious phenotypic effects. Of the latter nonsyndromic forms, the lidgap series includes four extant mutations that are considered to be alleles based on complementation tests. All show genetic complexity in segregation ratios. None has been mapped previously. On the basis of a strategy of mapping the mutation with the simplest inheritance pattern first, we generated an extensive exclusion map for lidgap-Gates, lgGa, using morphological and protein polymorphisms. We then screened the non-excluded regions in a congenic strain, AEJ.LGG-lgGa, for SSLP markers and located the differential chromosome segment containing the lgGa locus in a region near the distal end of mouse Chromosome (Chr) 13. This linkage was confirmed and refined by typing SSLPs in 64 F2 and 74 BC1 progeny of a cross of LGG/Bc (lgGa/lgGa) to SWV/Bc. The lgGa mutation maps to a 1- to 2-cM region between D13Mit76 and D13Mit53. Integrin alpha 1 and integrin alpha 2, which map to the same general region, are possible candidate loci, based on their embryonic expression and cellular function. Evidence is also presented for a common unlinked recessive suppressor of the open eyelids trait caused by lgGa.

The major locus for multifactorial nonsyndromic cleft lip maps to mouse chromosome 11.

Cleft lip with or without cleft palate, CL(P), a common human birth defect, has a genetically complex etiology. An animal model with a similarly complex genetic basis is established in the A/WySn mouse strain, in which 20% of newborns have CL(P). Using a newly created congenic strain, AEJ.A, and SSLP markers, we have mapped a major CL(P)-causing gene derived from the A/WySn strain. This locus, here named clf1 (cleft lip) maps to Chromosome (Chr) 11 to a region having linkage homology with human 17q21-24, supporting reports of association of human CL(P) with the retinoic acid receptor alpha (RARA) locus.

Bases for the early immune response after rechallenge or component vaccination in an animal model of acute Mycoplasma pneumoniae pneumonitis.

The pathology of Mycoplasma pneumoniae pulmonary infection for a hamster model was examined after whole bacterium rechallenge or component vaccination. Animals which, after an initial infection, were rechallenged with either live or heat-killed M. pneumoniae inocula developed severe early recall lesions in the first 3 days. In contrast, animals infected once develop maximum histopathology at approximately 10-14 days. A severe perivascular inflammatory cellular infiltrate developed in the rechallenged groups, and pulmonary pathology could also be elicited by rechallenge with bacterial growth medium components. Component vaccination with protein P1 did not reduce disease in comparison to once-infected controls, and vaccination promoted an early immune recall response as well. We conclude that an early immune response needs to be sought in all future experiments of challenge/rechallenge or vaccination. Vaccine studies will require an understanding of both protective and harmful immunogens.

A continuing assessment of risk factors for the development of Escherichia coli O157:H7-associated hemolytic uremic syndrome.

Univariate and multivariate analyses were applied to determine risk factors for the progression of Escherichia coli O157:H7 enteritis to hemolytic uremic syndrome (HUS). Both clinical and laboratory variables were assessed for 118 pediatric patients (28 HUS; 90 enteritis only). Verotoxins 1 and 2 were produced by 89% of E. coli strains whereas verotoxin 2 only was produced by 11%. Although a greater frequency of strains producing verotoxin 2 only occurred in HUS isolates (p = 0.11), toxin phenotype was not significantly associated with risk after multivariate analyses. HUS patients with or without neurological manifestations had similar frequencies of the two toxin phenotypes among their isolates. Significant associations for young age (RR = 0.984; 95% CI = 0.971-0.998) and prolonged use of antidiarrheal agents (RR = 44.11; 95% CI = 8.48-229.4) with HUS were apparent. A lesser chance of progression was observed for patients whose strains possessed a 4 kb plasmid (RR = 0.27; 95% CI = 0.08-0.94). Our results are consistent with the hypothesis that progression to HUS is dependent upon both bacterial virulence factors and the clinical characteristics of the individual patient.

Immunodominant antigens of Streptococcus equisimilis shared by other beta-haemolytic streptococci.

Three immunodominant antigens of Streptococcus equisimilis (Lancefield group C) with approximate mol. wts of 46, 66 and 105 kDa were recognised by human serum IgG and IgA immunoblotting. These antigens were identified consistently by various human sera but immunoblots with IgA (heavy chain) and secretory IgA (J chain) from human respiratory secretions gave more variable results. Antigens with similar migration rates were demonstrated in S.pyogenes, large colony human biotype group G streptococci, and streptococci of groups C and G from the "S. anginosus-milleri group". Polyclonal antibody which was eluted from immunoblot substrates that contained the S. equisimilis 66-kDa antigen reacted with the 60-kDa antigen of S. pyogenes. Both polyclonal and monoclonal anti-vimentin antibodies identified the 46-kDa and 66-kDa antigens of S. equisimilis. The homology of these antigens among beta-haemolytic streptococci has the potential to complicate both a strategy for the utilisation of immunoblotting for diagnostic purposes and the understanding of how such antigens may be involved in the pathogenesis of post-infectious sequelae.