Seiichi Mori

Development of peripheral lymphoid organs and natural killer cells depends on the helix-loop-helix inhibitor Id2.

Transcription factors with a basic helix–loop–helix (HLH) motif have been shown to be crucial for various cell differentiation processes during development of multicellular organisms. Id proteins inhibit the functions of these transcription factors in a dominant-negative manner by suppressing their heterodimerization partners through the HLH domains. Members of the Id family also promote cell proliferation, implying a role in the control of cell differentiation. Here we show that Id2 is indispensable for normal development of mice. Id2−/− mice lack lymph nodes and Peyers patches. However, their splenic architecture is normal, exhibiting T-cell and B-cell compartments and distinct germinal centres. The cell population that produces lymphotoxins, essential factors for the development of secondary lymphoid organs, is barely detectable in the Id2−/− intestine. Furthermore, the null mutants show a greatly reduced population of natural killer (NK) cells, which is due to an intrinsic defect in NK-cell precursors. Our results indicate that Id2 has an essential role in the generation of peripheral lymphoid organs and NK cells.

Id2 haploinsufficiency in mice leads to congenital hydronephrosis resembling that in humans

Congenital hydronephrosis is one of the most common anomalies found in humans and may cause renal failure in childhood. Half of the cases are due to obstruction at the ureteropelvic junction (UPJ). Here we report that mice lacking Id2, an inhibitor of basic helix‐loop‐helix (bHLH) transcription factors, exhibit hydronephrosis mimicking the characteristics of human cases such as unilaterality and male preponderance. Hydronephrosis was found even in Id2+/– mice. The penetrance was 67.2% in Id2−/– males, 48.8% in Id2+/– males, 28.0% in Id2−/– females and 20.0% in Id2+/– females. Distortion or high insertion of the ureter at the UPJ was frequently observed and these morphological changes were evident in late embryogenesis. Histologically, the muscle layer, where Id2 is normally expressed, was hypertrophic and/or irregular at the UPJ. Furthermore, gene expression analysis suggested that BMP4 (bone morphogenetic protein 4), which is known to be involved in the development of hydronephrosis, appears to function as an upstream factor of Id2. Our results thus raise the possibility that Id2 is a gene responsible for the pathogenesis of hydronephrosis in man.

Factors Associated With and Fitness Effects of Nest-Raiding in the Three-Spined Stickleback, Gasterosteus Aculeatus, in a Natural Situation

The occurrence and consequences of nest-raiding behaviours of male three-spined sticklebacks (Gasterosteus aculeatus L., forma leiura) were studied in an enclosed section of a small stream of the Tsuya River, Gifu Prefecture Central Japan. The observations were made almost daily on 99 males which were individually marked and the 189 nests built by them during the breeding season, March to mid July 1988. About 10% of the nests were subjected to raiding which included egg cannibalism, egg stealing and sneaking fertilizations. Most raidings were done by single territorial males. The probability of nest raiding was related to the degree of cover around the nest: nests in dense vegetation were most prone to raiders. The probability of raiding was further related to the stage of the nest: nests with eggs were most liable, those with fry least liable to raiding actions. Males that performed raiding behaviour could have nests in every stage, but most likely had no eggs in their nests. The probability of being raided was thus positively related to the number of neighbouring nests without eggs. Males that raided had a significantly duller overall nuptial coloration during the egg collecting phase than non-raiders. Body size and territory size did not differ between raiders and non-raiders. Raiders may thus be less attractive to ripe females. By egg stealing they may increase the attractiveness of their otherwise empty nest to spawning. Indeed, nests of raiders produced significantly more often young than those of non-raiders, but the number of young produced in successful nests was not different between the two categories of males. Nest-raiding was detrimental to the victims of raiding actions: raided nests produced less offspring early in the breeding season.

Two morphological types in the reproductive stock of three-spined stickleback, Gasterosteus aculeatus, in Lake Harutori, Hokkaido Island

SynopsisTwo morphological types of the trachurus form (completely plated morph) of three-spined stickleback, Gasterosteus aculeatus, are found in Lake Harutori, Kushiro, east district of Hokkaido Island. For convenience, the two forms are referred to as ‘large type’ and ‘small type’ on the basis of body length (discrimination at 70 mm in length). The two types were examined for morphometric, meristic and reproductive characteristics. They differ in body length, the number of lateral plates, means of the 2nd dorsal spine length/body length and of the pelvic spine length/body length, the relationship between body length and head length, between body length and gonad weight, between body weight and gonad weight, and between body length and ovarian egg number; significant differences were present for each sex. These two types were compared with the anadromous stickleback migrating into the freshwater area near Lake Harutori to breed. The anadromous fish was morphologically much more similar to the large type than the small type. It is suggested that the large type is also an anadromous form and the small type is the permanent freshwater resident.

The leukemic oncogene tal-2 is expressed in the developing mouse brain.

tal-1 (T-cell acute leukemia-1; also known as SCL) and tal-2 genes belong to a family of basic helix-loop-helix transcription factors and were originally isolated from the breakpoints of chromosomal translocations in human T-cell leukemia cell lines. tal-1 is expressed not only in hematopoietic cells but also in several endothelial structures and the central nervous system during development. On the other hand, the detailed function and the sites of expression of tal-2 have remained obscure. We cloned the tal-2 cDNA from a mouse embryonic cDNA library and examined its expression pattern in the mouse, comparing with that of tal-1. In situ analyses revealed that tal-2 transcripts are detected at embryonic day 12.5 in the following regions; 1) the diencephalon-the zona limitans intrathalamica and the pretectum, 2) the mesencephalon-the tectum, and the anterior and posterior tegmentum, 3) the metencephalon-the isthmus and the anterior pons. In the diencephalon and the mesencephalon, the expression sites of tal-2 gene were similar to those of tal-1, and its expression was stronger than that of tal-1. In the metencephalon, tal-2 expression was observed in the anterior pons, whereas tal-1 transcripts were detected in the entire pons, and showed stronger expression than tal-2. The tal-2 messages were barely detectable in the brain at birth. These results suggest that tal-1 and tal-2 are involved in the development of specific areas of the central nervous system.

The Helix-Loop-Helix Inhibitor Id2 and Cell Differentiation Control

Transcription factors play pivotal roles not only in the regulation of cellular functions but also in the control of cell differentiation. They can be classified on the basis of their structural features, i.e. motifs that mediate functional properties such as DNA binding and protein-protein interactions. The family of helix-loop-helix (HLH) factors is one of the well-studied examples [1-3]. Most members have DNA binding activity and directly regulate the expression of their downstream genes. Some, however, do not bind DNA and negatively regulate the functions of other HLH transcription factors at the protein level [4, 5]. These HLH inhibitors are called Id, inhibitor of DNA binding/differentiation [4, 5]. Here we focus on and describe the immunological aspects of mice lacking Id2.

Spatial and temporal variations in nesting success and the causes of nest losses of the freshwater three-spined stickleback, Gasterosteus aculeatus

SynopsisNesting success in populations of the three-spined stickleback Gasterosteus aculeatus (leiurus form), that permanently inhabit the freshwater area with springs recorded 302 nests in the spring areas and 147 in the main stream of the Yamayoke River, Gifu Prefecture in Central Japan. The three-spined sticklebacks showed temporal variation in nesting success within sites together with spatial variation between sites. The rate of nesting success averaged 27.8%. There was no apparent seasonal trend in nesting success. Nest density varied over time and between sites but was not associated with variation in nesting success. Nesting losses were partly caused by rapid currents after rain or lack of water during the dry period. Conspecific and heterospecific disturbances also caused some losses. Heterospecific pressure was greater in the main stream than in spring areas. Some males spontaneously abandoned their nests and renested even without external impacts.

Detection of mRNAs in Peyer’s patches of the developing mouse embryo

We describe a method to identify cells expressing mRNA of interest in the developing digestive tract by whole mount in situ hybridization with digoxigenin-labeled RNA probes. In preparing samples, serosal tissue surrounding the intestine was removed. Enzymatic reactions and probe concentrations were optimized. Furthermore, polyvinyl alcohol was included in the reaction mixture for the color development of alkaline phosphatase conjugated to the antibody against digoxigenin. These modifications improved the sensitivity and enabled us to identity cells that express mRNA in embryonic intestine. Using the antisense probe for VCAM-1, the protein product of which is an immunohistochemical marker of the Peyers patch in the embryonic intestine, cells expressing mRNA were identified as spot-like clusters in Peyers patches, confirming the validity of the method. With this method, mRNAs of both lymphotoxins alpha and beta, key molecules for peripheral lymphoid organ development, were found to be confined to the Peyers patch in the developing intestine. Whole mount in situ hybridization analysis is a useful tool for exploring spatio-temporal expression profiles of mRNA in the developing immune organs.

The upright nesting behaviours on a vertical shore-wall in the three-spined stickleback,Gasterosteus aculeatus (leiurus form)

For the three-spined stickleback, there have been numerous descriptions of nesting behaviours on the bot tom substrate, based on both laboratory and field observations (Tinbergen 1951; van Iersel 1953; Sevenster 1961; van den Assem 1967; Hagen 1967; Wootton 1976, 1984; Kynard 1978; Pressley 1981; FitzGerald 1983; Mori 1985). However, this report provides the first observations of the unusual breeding behaviours performed on a vertical shore-wall (Fig. 1). Observations of nesting three-spirted sticklebacks were made along the right shore (within 1 m distance from the bank) of one of the small inlet streams in the Tsuya River (Mori 1987a); this river is a tributary of the Ibi River and is situated at an elevation of 5 m above sea level in the southwest (approximately 35 ~ 09 ~ N) of Gifu Prefecture, Japan. The Tsuya River has relatively abundant spring areas and some inlet streams along the right shoreline (Mori 1985, 1987b). The inlet stream studied in this paper is 60 m in length, 2.5 m in width and 2 0 7 0 cm in depth, with springs as the water source, and is a ditch made of concrete plates on both sides. The stream bed is covered mainly with mud and partially with sand. Although ecological study of this stream was made from 5 to 22 times per month, from 1984 to 1987, the upright breeding behaviours were found only in spring 1986. The maximum number of normal nests per day in this study area was 121 on May 14th and a total of 324 nests including unsuccessful ones were observed during the 1986 study (Mori in preparation). These nests were maintained for 18.4 days on the average. On the other hand, for the unusual nests, observations over a total period of 12.5 h were carried out in the lower part of the stream during March to early April 1986. The nests on the vertical shore-wall were found for 6 males on the peak day and recorded at a total of 12 different sites during the study period (Fig. 2). This nesting phenomenon occurred within the period of March 20th to April 8th. During the beginning of the breeding season, March 8th to 18th, nuptially coloured males with the territory at the upper part of the water layer were recorded at various regular points. On March 20th, I found that some males which might have earlier obtained territories in the upper port ion of the water layer were building the upright nests on the shore flank. The vertical nesting behaviours were observed in 12 nests. The nests persisted for 7.9 + 6.2 days (mean + SD, range: 1 -19 days). These unique nests were seen at a nook between a pile and the shore wall where the water was too deep ( 4 8 6 5 cm in depth) for normal nests, which are generally built on the stream bottom, at 20 -35 cm in depth (Mori in preparation). The distance from the nest to the bot tom was about 40 cm. Below such nests there were often some normal nests on the bot tom substrate (Fig. 2, Table 1). Assuming an upright posture with head up, 5 males (nest codes 1, 3, 6, 8 & 9) both pushed their snouts into their nests and fanned to ven-

Dyadic relationships in nesting males of the three-spined stickleback, Gasterosteus aculeatus

Multidimensional scaling analysis of nest site location, nesting interval, and aggressive and mating interactions revealed that male three-spined sticklebacks, Gasterosteus aculeatus, formed nesting clusters comprising five patterns of dyadic relationships. These patterns were defined by intervening variables such as size difference between the two males, nest site locations, synchronization of nesting cycles (egg presence in the nest), distance between two nests, and nest raiding behaviours. Several patterns of dyadic relationships were integrated among nesting males and their constellations indicated an expression of the social structure. Through an understanding the social structure, I described effects of social context or situations on individual reproductive success.