Sumiko Kimura

Sequential changes of programmed cell death in developing fetal mouse limbs and its possible roles in limb morphogenesis

Apoptotic cell death in the developing limb of mouse fetuses was examined sequentially on days 11–15 of gestation by means of Nile blue (NB) sulfate staining with special reference to its relation to limb morphogenesis. With some exceptions, programmed cell death (PCD) in the hand and foot was observed in the mesenchyme but not in the surface ectoderm. We found that during digital formation PCD begins at the proximal portion of the interdigital mesenchyme and subsequently expands distally. Therefore, the initial PCD that occurs in the interdigital zones may determine the proximal ends of digital separation and also contribute to the demarcation between the palm (sole) and digits (toes). During digital separation, the areas of PCD in the interdigital zones were found to become larger and expand distally on day 13, which may be necessary for the separation of digits and for determining the interdigital area to disappear. PCD in presumptive phalangeal joints was also found to proceed from proximal to more distal joints. The PCD in presumptive joints may be required for the separation of phalanges and metacarpal (metatarsal) bones and for the formation of joint cavities. In addition, intense PCD was observed in the radial (tibial) and ulnar (fibular) margins of the hand and foot plates for 4–5 days. Such PCD at marginal areas seems to prevent the formation of supernumerary digits (preaxial and postaxial polydactyly) and other digital malformations. Therefore, the timing when PCD commences and ends, the sites where PCD occurs, and the intensity, duration, and proximo‐distal progress of PCD appear to be genetically determined, and the elimination of unnecessary cells by PCD may be essential for normal limb morphogenesis. The present findings also suggest that the normal progress of PCD in the hand and foot plates of rodent fetuses may prevent the formation of some limb malformations such as webbing fusion of digits, polydactyly, or cleft hand/foot.

Fetal and postnatal development of palmar, plantar, and digital pads, and flexion creases of the rat (Rattus norvegicus)

Fetal development of the hands and feet of rats was investigated to determine the feasibility of using rats as an experimental model for studying the factors influencing early development of the hands and feet, and especially the dermatoglyphics in humans. Eighty rat fetuses of 14–21 days gestational age and 80 newborn rats of 0–7 days of age were used to study the morphological features of the palmar, plantar, and digital areas and to determine the timing of appearance and the location of the volar pads and flexion creases. Comparisons between analogous developmental stages of rat and human fetuses demonstrate striking similarities in overall fetal development. Marked differences, however, were found between rat and human fetuses in the timing of developmental milestones and in some morphological features. The results indicate that rats can serve as a useful experimental model in studies of the utility of the epidermal ridge configurations and flexion creases in medical disorders, provided that the differences in the timing of development are taken into consideration.

Pads and flexion creases on the plantar surface of Hammertoe mutant mouse (Hm)

The purpose of the present work was to determine the effects of the hereditary malformation of Hammertoe mutant mice (gene symbol Hm) on the surrounding morphological structures and, specifically, on the volar pads, i.e., the sites of the epidermal ridge patterns (dermatoglyphics). The hindlimbs of the wild‐type (+/+) Hammertoe mice show no anomalies and their major pad and flexion crease configurations correspond to those of normal mice. The heterozygous (Hm/+) and homozygous (Hm/Hm) mice display a fusion of the interdigital tissues involving all digits with the exception of digit I. In Hm/Hm mice, this webbing extends to the distal phalanx and the markedly flexed digits form a shape resembling a hammer. In Hm/+ mice, the interdigital webbing does not extend as far and the digits show moderate flexion compared to those of Hm/Hm mice. Both Hm/Hm and Hm/+ have a rudimentary extra digit in the postaxial area of the hindlimbs. The ventral volar skin of the flexed digits is incompletely developed. The more posterior digits show the more severe camptodactyly. These aberrant configurations are related to the abnormal occurrence of the programmed cell death (PCD) in the interdigital zones II–IV and the proximal part of the postaxial margin during hindlimb development. They are limited to the pads on the plantar surface of the postaxial area; the preaxial area is not affected. As a result of a severe camptodactyly of digit V, its volar skin is shifted into the distal portion of the hypothenar area. This shifting affects the number, size, and location of the pads, especially of the hypothenar pad, resulting in varying pad configurations, such as a displacement of the distal and proximal components of the hypothenar pad, or a fusion of the two components of the hypothenar pad, leading to a reduced final pad number. These pad modifications are induced by the postaxial plantar surface shifting proximally and are not affected by the presence of an extra rudimentary digit. The pad modifications in Hammertoe mice with webbed digits and postaxial polydactyly resemble closely those of the previously studied mice with genetic preaxial polydactyly. Anat Rec 260:26–32, 2000.

Developmental Aspects of Human Palmar, Plantar, and Digital Flexion Creases

Unusual, extra of missing flexion creases have been reported in individuals with various medical disorders. Examples of such associations include the single transverse palmar flexion crease (“simian line”) and Sydney crease in Down syndrome (Beckman, Gustavson, & Norring 1962; Purvis-Smith & Menser 1968), “sandal” crease on the soles in Down syndrome (Penrose 1963) and the Rubinstein-Taybi syndrome (Rubinstein 1969; Filippi 1972), single interphalangeal crease on digit V in Down syndrome (Penrose 1931), trisomy 18 (Schaumann & Alter 1976; Hodes, Cole, Palmer, & Reed 1978) and partial trisomy 9p (Rodewald 1979), and missing distal interphalangeal flexion creases in a mentally retarded individual (Aue-Hauser 1979). Occasionally, unusual flexion creases are present in normal, healthy individuals (Davies & Smallpeice 1963; Alter 1970; Plato, Cereghino, & Steinberg 1973; Komatz, Daijo, & Yoshida 1978; Wertelecki 1979). The clinical significance of the flexion crease anomalies, however, is not well appreciated, mainly because of the limited understanding of the normal crease development (Lacroix, Wolff-Quenot, & Haffen 1984; Kimura and Kitagawa 1986; Stevens, Carey, Shah, & Bagley 1988; Kimura & Schaumann 1988). To fill this gap, we have studied the embryonal development and the morphology of the flexion creases on the surfaces of the palms, soles and digits in human fetuses.

Normal Location Of Thumb/Big Toe may be Related to Programmed Cell Death in the Preaxial Area of Embryonic Limb

The forelimbs and hindlimbs of newborn Polydactyly Nagoya (Pdn) mice were examined to analyze the roles of programmed cell death (PCD) in the preaxial region of the limb. Special attention was paid to the relationship between the PCD in the preaxial area and the location and shape of the first digit (thumb/big toe). Although a large, bifurcated or duplicated thumb/big toe appeared in Pdn/+ mice, digit I (thumb/big toe) in Pdn/+ mice, as in +/+ ones, was located more ventro‐proximally than the other four digits. On the other hand, abnormal preaxial digits of the fore/hindlimb in Pdn/Pdn mice lay distally and were aligned at the radial/tibial end of a serial curved plane formed by digits II–V; that is, a thumb and big toe of normal shape and location were not detectable in any preaxial digits of Pdn/Pdn mice. In the limb development of Pdn mouse embryos on Day 11‐12, PCD did not occur in the preaxial mesoderm of fore/hindlimb only in one‐fourths of all embryos obtained by Pdn/+ x Pdn/+ mating. In addition to digital rays II‐V, extra preaxial digital rays appeared in the prominent preaxial expansion of fore/hindlimbs in these embryos on early Day 12. These abnormal limb configurations in embryos were closely similar to those in Pdn/Pdn newborn mice. The present findings suggest that PCD in the preaxial region not only prevents the formation of extra digits but also determines the location of the thumb/big toe for the normal limb morphogenesis. Anat Rec, 2011.

Ectopic dermal ridge configurations on the interdigital webbings and postaxial marginal portion of the hindlimb in Hammertoe mutant mice (Hm).

The effects of the hereditary malformation of Hammertoe mutant mice (gene symbol Hm) on the digital pads and dermal ridge configurations on their hindlimbs were examined. In the wild‐type (+/+) mice with normally separated digits, dermal ridges developed only on the pads. Heterozygous (Hm/+) and homozygous (Hm/Hm) mutant mice, however, had a broad big toe, fused interdigital soft tissues, reduced claws, an extra rudimentary postaxial digit and camptodactyly. The dermal ridges appeared not only on the pads, affected in their number and configurations, but also on the ventral surface of the interdigital webbings and postaxial marginal area exhibiting an extra rudimentary digit and webbing. These aberrant configurations may be related to the abnormal occurrence of programmed cell death (PCD) in the interdigital zones and the postaxial marginal portion in Hm/+ and Hm/Hm mice. That is, the diminished cell death may fail to decrease the cell density in the interdigital zones and postaxial marginal portion and result in the webbing and an extra rudimentary digit and webbing, respectively. Simultaneously, it could also interrupt the migration of surviving cells of these areas toward the neighboring digits and the distal area of the sole and produce the ectopic dermal ridges on the way to the as yet unformed (presumptive) digital and plantar volar pads. The present findings suggest that normal interdigital and pre/postaxial PCD contributes not only to the separation of digits, the initial formation of individual digits of different sizes, and the inhibition of the extra digit but also to the development of the presumptive digital and plantar pads, including dermal ridges. J. Morphol., 2008.

Rudimentary claws and pigmented nail-like structures on the distal tips of the digits of Wnt7a mutant mice: Wnt7A suppresses nail-like structure development in mice.

BACKGROUND As Wnt7a mutant mice exhibit double ventral structures in the digits of autopods, it has been accepted that dorsal-ventral identity in limb development is regulated by the Wnt7a signal. The most important evidence for this was the presence of surface pads, typical characteristics of ventral structures, on the dorsal side of digital tips and at the base of digits and their pigmentation. METHODS The morphologic features of the appendages on the distal tips of digits were inspected in the fore- and hindlimbs of mice having a different Wnt7a mutation. The digital structures were examined macroscopically and histologically. RESULTS The Wnt7a homozygous mutant mice with defects in postaxial digits had rudimentary claws or claws and pigmented nail-like structures, instead of dorsal pads, on the distal digital tips and hairs on the dorsal surface of the digits of fore- and hindlimbs. Furthermore, pigmented ectopic nail-like structures but not pads were also present on the dorsal surface of the base of digits. Double ventral structures were observed in the bones and tendons, excluding pads in digital areas. CONCLUSIONS These findings suggest that Wnt7a is not necessarily an exclusive dorsalizing signal to the dorsal ectoderm of the digital areas of autopods. Rather, the Wnt7a signal may participate in suppression of the development of pigmented nail-like structures in normal limb development. This means that even rodents, a species lower than primates in the evolution from claws to nails, have molecular potential to develop cutaneous appendages similar to nails at their location.